Current protocols and outcomes of ABO-incompatible kidney transplantation
The demerit of transplantation from a living donor is that there’s high immunological incompatibility in about 30%.
To overcome the obstacle of incompatibility, different strategies are used:
· Desensitization of the recipient to remove the antibodies and to prevent their rebound after transplantation.
· Kidney Paired Donation(KPD). The exchange of organs between two or more pairs.
Evolutionof practice in ABOi-rTX:
· Renal transplantations from A2 donors to O recipients: better results in transplantation involving ABOi are obtained when transplanting kidneys from A2 donors to O recipients. The A2 subtype does not have circulating antigens linked to von Willebrand factor.
· The Japanese strategy was the splenectomy associated with their pretransplantation protocol.
· The strategy of Johns Hopkins University and the Mayo Clinic in the United States; administration of RTX to replace splenectomy.
· Swedish strategy; using antigen-specific immunoadsorption and rituximab for the ABO-incompatible kidney transplantatio.
Desensitization strategies
The frequently used strategies for desensitization are:
1. Removal of circulating antibodies; by plasmapheresis or immune-adsorption.
· Plasma exchange using highly permeable membranes; simple and chief but less effective.The procedure eliminates approximately 20% of the antibodies by session. Additionally, removes protective antibodies and coagulation factors.
· DFPP is performed by two plasma filters, and the second one allows smaller molecules to return back to the patient, avoiding many complications associated with the therapeutic plasma exchange.
· IA; evolution has been made by the use of columns for the selective removal of humoral factors by IA. The advantage of IA is its high capacity to induce ABO agglutinin removal with high biocompatibility and without complement activation.
Types of columns for IA are:
(i) IA with immobilized antibodies: A Therasorb column contains polyclonal sheep anti-human IgG antibodies,which is effective in removal of IgG antibodies. Immunosorba columns, that contains staphylococcal protein A bound to sepharose is effective in removing IgG of different classes.
(ii) IA technique uses immobilized antigens and synthetic epitopes; most specific technique in removing only the undesirable antibodies. The main steps in the evolution of desensitization:
§ IA or PP2-3 times before Tx plus splenectomy.
§ PP + IVIG + RTX before Tx(no splenectomy).
§ IA and RTX before Tx + LMWH(no splenectomy).
1. Immunomodulation technique : viaadministration of high doses of polyclonal intravenous immunoglobulin (IVIG) to the patient before transplantation. The aims of IVIG:
• Replacement of IGs that being lost by apheresis techniques.
• It blocks the Fc portion.
• It has immuno-regulatory effect.
2. B cell depletion via splenectomy or RTX.
Clinical outcome after ABOi-rTX
· Transplants involving ABOi compared to those involving ABOc had a significantly higher mortality rates at 1, 3 and 5 years.
· Both graft losses and mortality in transplants involving ABOi became equivalent to ABOc transplants at 8 years after transplantation.
· Coagulation disorders were frequent in transplant involving ABOi.
· Polyoma virus nephropathy was more frequent in patients receiving RTX.
· Many reports document outcomes similar to the standard transplantations leading to controversies and a need to further RCT. Main controversies in ABOi-rTX:
· Technique of apheresis
· Role of RTX
· IVIG
· Isoagglutinin quantification
· Immunosuppression
· Post-transplantation apheresis
· Accommodation
· Role of protocol biopsies
· Complications
Alyaa Ali
2 years ago
renal transplantation is the optimal management for ESRD, about 30% of patient on the waiting list of transplantation have incompatible donor ( HLA or ABO incompatible )
the solution is the finding of compatible donor deceased or living .
if they have incompatible donor they can wait for compatible one but this option is risky or to do kidney paired exchange or to receive the organ from incompatible donor through de-sensitization. Immunological aspects
At the renal level,the antigens of the ABO system are expressed on the collecting and distal tubules and on the vascular endothelial cells
Group O individuals have higher antibody titers to both the A and B antigens. As a consequence, recipients of blood type O have a higher incidence of antibody-mediated rejection (ABMR) after transplantation
Better results in transplantation involving ABOi are obtained when transplanting kidneys from A2 donors to O recipients. The A2 subtype does not have circulating antigens linked to von Willebrand factor.
The reaction of isoagglutinins with the antigens of the ABO group induces complement activation, as documented by the presence of C4d
Techniques of ABO desensitization and different protocols used over time
Removal of circulating antibodies
it is done several days before transplantation, to reduce the circulating anti-A/B antibody levels to achieve titers between 1:8 and 1:32
Plasma exchange eliminates approximately 20% of the antibodies by session. Additionally, removes protective antibodies and coagulation factors.
The double filtration plasmapheresis s is performed by two plasma filters, and the second one allows smaller molecules to return back to the patient, avoiding many complications associated with the therapeutic plasma exchange.
Selective removal of humoral factors by IA
Immunomodulation
by administration of high doses of polyclonal intravenous immunoglobulin (IVIG) to the patient before transplantation, to replace the patient’s immunoglobulins lost because of apheresis techniques.
B cell depletion B
B cells produce isoagglutinins, and their reduction is essential to obtain effective desensitization. Historically, splenectomy has been used for B cell depletion. To date, RTX, a humanized monoclonal antibody that binds to CD20 expressed on the B cell membrane, is the drug used to obtain B cell depletion. the aim of B cell depletion is to reduce the agglutinin titer to a predetermined level.
Clinical outcomes after renal transplantation involving ABOI
By 2007, Genberg et al.,showed that there was no significant difference in patient and graft survival or in the rejection episode rates.at 3 years follow up between patients with ABO compatible renal transplantation and Incompatible recipients who were treated with IA and a single dose of RTX (375 mg/m2 of body surface) 30 d before transplantation and IVIG at a dose of 0.5/kg body weight in the day before transplantation.
A more recent and wider systematic review gives different results . This review examines 7098 renal transplantations involving ABOi.Overall, transplants involving ABOi compared to those involving ABOc had a significantly higher mortality rates at 1, 3 and 5 years . Both graft losses and mortality in transplants involving ABOi became equivalent to ABOc transplants at 8 years after transplantation.The higher mortality rate is probably a consequence of the high immunosuppression related to the therapy.
Immunosuppression
Apart from desensitization, the immunosuppression in kidney transplantation with ABOi is similar to that used for standard transplantation. The basal immunosuppression begins together with the desensitization. The possibility of steroid withdrawal is discussed. Some studies have documented a high risk of ABMR in the case of steroid withdrawal soon after transplantation. Other studies have documented a high risk for acute rejection even in the case of late withdrawal.
Accommodation
In the presence of circulating antibodies and antigens on the graft cell surface, the graft itself may not be rejected.
The pathogenesis of the accommodation seems to be due to the presence of a low titer of antibodies, with low affinity and with the blockage of complement activation . Under these conditions, endothelial cells develop a phenotypic change according to which they become resistant to antibody damage.
the presence and the role on protocol biopsies of C4d in transplantations involving ABOi seems to be related to accommodation when found in the absence of clinical or other histological abnormalities.
Complications
Surgical complications in transplantations involving ABOi are similar to complications of standard transplants, with the exception of hemorrhages.
increased incidence of infection
ABMR is the first cause of graft loss in transplantations involving ABOi .
Kidney paired donation (KPD)
The hypothesis of overcoming the immunological barriers in a different way without the desensitization of the recipient was first proposed by Rapaport in 1986. The simplest model of the KPD is the two-way.
Indeed, given the fact that KPD is generally cheaper with respect to desensitization.
MICHAEL Farag
2 years ago
Introduction Renal transplantation is considered the best therapy for patients affected by end-stage renal disease. or such patients, to avoid a long time on dialysis, transplantation from living donor is the best option. However, approximately 30% of such transplantations are considered incompatible from the immunological point of view either because of the presence in the recipient of antibodies directed against the human leukocyte antigen (HLA) antigens of the donor or because of the incompatibility of the ABO system between the donor and recipient or because of both. There are two principal strategies to overcome these barriers: To desensitize the recipient to remove the antibodies and modify the immunological status, allowing the transplant; and To exchange the organs between two or more pairs to exchange the organs between different donors. TECHNIQUES OF ABO DESENSITIZATION AND DIFFERENT PROTOCOLS USED OVER TIME A) Removal of circulating ABO antibodies The removal of circulating ABO antibodies is obtained principally by plasmapheresis or immune-adsorption (IA). The aim of these strategies, principally applied several days before transplantation, is to reduce the circulating anti-A/B antibody levels to achieve titers between 1:8 and 1:32.
B) Immunomodulation his technique consists in the administration of high doses of polyclonal intravenous immunoglobulin (IVIG) to the patient before transplantation. The aim is to replace thepatient’s immunoglobulins lost because of apheresis techniques. In addition, IVIG blocks the Fc receptor and has immunoregulatory properties. C) B cell depletion B cells produce isoagglutinins, and their reduction is essential to obtain effective desensitization. In the past, it was done by spenectomy but we use anti-CD20 (rituximab) Initially, the most frequently used technique was the removal of circulating anti-ABO antibodies by plasmapheresis. The technique is effective but has the disadvantages of removing blood components that are useful to the patient and causing coagulation disorders. More recently, principally in Europe, plasmapheresis has been replaced by the technique of the IA of isoagglutinins using specific protein A or anti-human Ig columns. The main advantages of this technique are to its high capacity to induce ABO agglutinin removal with high biocompatibility and without complement activation. Since then, almost all desensitization strategies used the administration of IVIG to improve immunomodulation and the administration of RTX to avoid splenectomy. More recently, at the Guy’s Hospital, Barnett et al adopted a tailored desensitization strategy in pairs with ABOi. The different strategies were adopted according to the initial anti-ABO antibody titer. With a titer of 8, only RTX was used; with a titer between 16 and 64, plasmapheresis was added to RTX therapy; and with a titer > 64, IA and RTX were used. In total, 62 kidney transplants involving ABOi were performed using this strategy, and the results were compared with 167 ABOc transplants. No difference was observed between the two groups in allograft and patient survival rates at 1 and 3 years or in the ABMR rates.
These results highlight that a tailored desensitization strategy obtains good results with personalized therapy and lower costs.
Mahmud Islam
2 years ago
Renal transplantation as the best choice for ESRD is faced with difficulties in finding full matched donors. this is solved either by desensitisation or paired donation. In this review, the current protocols of desensitization are summarized. since the introduction of ABO incompatible transplant recently, rituximab replaced splenectomy, as well as advancements in plasmapheresis techniques.
Recipients with blood group O have the most chance of AMR because of the chance of having antibodies to both A and B blood groups.
blood group A2, on the contrary, have the lowest risk. They do not have circulating antibodies linked to VWF.
ABO antigens reaction with isoagglutinin seems to activate complement as shown by c4d deposition.
With the improvement of AMBR treatment protocols and techniques of desensitization in addition to rituximab, the ABOi tx dramatically increased in the last decades.
Techniques of ABO desensitization used over time can be summarized as techniques for the removal of circulating ABO antibodies, immunomodulation and B cell depletion.
Removal of circulating ABO antibodies:
principally by plasmapheresis or immune-adsorption. The aim is to lower the ab titers to less than 1:32 (1.8-1:32) several days before transplantation. plasmapheresis removes nearly 20% in each session. double filtration is done to lower complications associated with standard plasmapheresis by allowing smaller molecules to return to the patients. Immune-adsorption allows selective removal of certain antibodies. here are two types of IA columns: sheep or those containing staphylococcal protein A.
Immunomodulation: By giving polyclonal IVIG, we replace the patients’ immunoglobulin. IVIG also blocks the Fc receptor and also has immunoregulatory properties.
B cell depletion
B cells produce isoagglutinin. For this reason, it is very important to reduce them for effective desensitization. Historically splenectomy was used. After the introduction of anti-CD20, Rituximab replaced splenectomy.
….
When exposed to a low titer of ABO antibody, the transplanted kidney develops a capacity to resist complement activation. This long-lasting phenomenon is known as ACCOMMODATION.
Different techniques and protocols developed over time. Immuadsorption has fewer side effects, especially regarding hypercoagulability seen after plasmapheresis. some centres used only rituximab for low titers of antibodies.
Mohamed Essmat
3 years ago
ABOi kidney transplantation and KPD are the ways used to the overcome shortage of deceased donor organs and to allow patients to avoid long waiting time on dialysis.
ABO system antigens are expressed on RBCs, tubules and vascular endothelium.
ABOi was a contraindication for kidney transplantation.
However, ABOi transplants increased worldwide due to improvement in diagnosis and treatment of AMR.
The outcomes of ABOi transplants were similar to those with standard risk.
Techniques of ABO desensitization and different protocols used:
Removal of circulating ABO antibodies:
Plasmapheresis removes 20% of antibodies per session .
Double filtration PP is safer than PTx.
High dose of IVIG used to replace immunoglobulins lost with apheresis techniques in addition to its immunoregulatory effects to decrease antibody rebound and risk of AMR.
Now rituximab replaced splenectomy to obtain B cell depletion to decrease agglutinin titer to predetermined level.
A systemic review examined 83 studies highlighted the efficacy of rituximab and IA but was limited by absence of randomized controlled trials.
A wider systemic review showed that ABOi transplants have significantly higher mortality rates than ABOc transplants at 1,3 and 5 years, mostly due to intense immunosuppression causing severe infections.
Role of rituximab is not well determined and seems to be unnecessary in some patients.
The effect of steroid withdrawal either early or low is not well studied.
Accommodation is lack of rejection in presence of circulating ABO antibodies with normal kidney function and normal histology.
It is facilitated by reduction of isoagglutinin levels, blocking of complement activation and rituximab.
Balaji Kirushnan
3 years ago
Current protocols and outcomes used in ABO incompatible renal transplantation
Living donor incompatible renal transplants are now possible after HLA desensitization or ABO antibody removal technique. by performing ABO incompatible renal transplants we can increase the donor pool and reduced the waiting time of the patients on dialysis….
ABO incompatible renal transplantation came into picture after the year 2000…Initially Japan used to perform a lot of ABO incompatible renal transplants due to a poor deceased donor program in the beginning…Their protocols used splenectomy initially before 2002 due to regulatory use of rituximab by their own National health service…After 2002, japan has used rituximab in ABOi renal transplants and their results re extensively published. Later, Mayo and the European (Stockholm and Belgium) published their experience on ABO incomaptible renal transplantation using IA techniques and IVIG…
Antibody removal technique can be divided into the following
Antibody removal techniques:
This is done using Plasmaphresis and IA technique.. Plasmaphresis involves removing the plasma volume and replacing the volume with FFP of the AB type blood group..It has the disadvantage of normal coagulation factors and non specific immunoglobulin removal too…Although cheaper than IA, it is associated with infections and coagulation parameters….The DFPP using another plasma filter after removal that allows the return of the normal immunoglobulins and makes it more selective…Immunoadsorption techniques removes the antibody based on adsoprtion principle. Various adsorption columns are available…IA using staphylococcal protein A and aother coloumn using polyclonal sheep antibody are available….
IVIG:
This is given just before the time of surgery in some transplant protocols to replenish the Ig lost during the apheresis sessions and act as an immunomodulator after transplants….
B cell depletion technique:
It started with splenectomy in the 2000’s but later it was replaced by rituximab in many centers…Rituximab has been used in most of the modern day protocols with standard 2 doses of 375mg/m2 given minus 2 weeks post transplant. Various studies have evaluated Inj rituximab 200mg IV as a part of ABO densensitization protocol…
Many centers use a tailored imunosuppression protocols for ABO desensitization….
Issogluttin titre <1:8 – direct transplant
1:8 – Rituximab 1 dose
16-64 – Rituximab + DFPP
>64 – Rituximab + IA
The overall mortality and patient outcome as per various studies are comparable to ABOi vs ABOc renal transplants till a metanalysis published in the LANCET 2019….After this robust metanalysis which compared nearly 40 studies across various continents proved that ABOi renal transplants have a higher mortality as compared to ABOc renal transplants at 1,3,5 years… more than 8 years there was no difference in the outcome between ABOi and ABOc renal transplants….
Wee Leng Gan
3 years ago
Current protocols and outcomes of ABO-incompatible kidney transplantation
Living donor ABO incompatible kidney transplantation has become safe and effective due to the advancement of recipient desensitisation protocol and kidney paired donation. Desensitisation protocol include antibody reduction by plasmapheresis or immune-adsorption (IA); Inhibition of antibody production by splenectomy which has been replace by Rituximab recently; Pleiotropic action of IVIG; and Complement inhibition by eculizumab.
Plasmapheresis or immune-adsorption (IA) involve removal of circulating ABO antibodies in the recipients before transplantation. The antibody titers between 1:8 and 1:32 is desirable . Double filtration plasmapheresis allow returning of protective antibodies and coagulation factors this lowering the risks associated with therapeutic plasma exchange. On the other hand, the most specific IA technique that applying the immobilised antigens and synthetic epitopes to remove only the undesirable antibodies.
Immunomodulation by using high dose of polyclonal IV IG replace the immunoglobulins loss during apheresis. IV IG block the Fc receptor on the leukocyte membrane; Inhibit the complement activation and circulating antibodies towards HLA.
For effective B cell depletion IV Rituximab has been replaced splenectomy in most desensitising protocol. However, post-transplant plasmapheresis should be avoided if IV Rituximab is used at desensitisation protocol. This is because plasmapheresis can reduce Rituximab efficacy by removing it from circulation.
Accommodation is defined as presence of circulating isoagglutinins and antigens on the graft cells with normal renal function and positive C4d on the peritubular capillaries. Eculizumab, a monoclonal antibody against C5, may facilitate accommodation and serve as rescue therapy in the case of severe antibody medicated rejection ( ABMR ).
The complications of ABO incompatible renal transplant include are the same as ABO compatible renal transplant except risk of bleeding is generally higher in ABO incompatible group who received apheresis treatments. Infection risk is dependent on intensity of desensitisation strategy. The incidence of ABMR ranges between 10% and 30% especially in the first 2 weeks following transplantation.
The controversies in ABO incompatible renal transplant include apheresis technique used, role of rituximab, utility and role of IVIG, method to detect isoagglutinins quantity, type of immunosuppression and post transplantation apheresis, accommodation, role of protocol biopsies and complications.
Kidney pair donation ( KPD ) program ( K may overcome the immunological barrier of kidney transplantation. There are some issues pertaining to KPD such as transportation of kidneys and donor travel, simultaneous versus no simultaneous exchanges and whether the transplant process is a closed chains or open chains.
In my opinion, we need to personalise the desensitising protocol and immunosuppressive regimen for ABO incompatible kidney transplantation. However, we need to bear in mind that ABO incompatible generally more costly as compare ABO compatible renal transplant. Risks ABO incompatible transplant should be explained to potential recipients. KPD may serve as alternative to over come the immunological barrier.
Ramy Elshahat
3 years ago
ABO incompatibility is approximately 30% of the immunological barrier for solid organ transplantation because of the presence in the recipient of antibodies directed against the human leukocyte antigen system of the donor. Two different strategies are used to overcome these barriers: desensitization of the recipient to remove the antibodies and the exchange of organs between two or more pairs. There is no overall agreement on desensitization protocols, types, and doses of immunosuppressive medications. There are no large RCT studies to be sure of the optimum management. The target is to get successful transplantation with the least complications and use the least amount of immunosuppressive medications to decrease complications and cost.
The major 4 cornerstones in ABOi transplantation include (in order to reach anti-A/B antibody titers between 1:8 and 1:32)
· removal of antibodies using plasmapheresis, IA, DFPP
o plasma exchange: is a simpler, cheaper, but less effective technique that has been the using highly permeable membranes. The procedure eliminates approximately 20% of the antibodies
o The double filtration plasmapheresis: is performed by two plasma filters, and the second one allows smaller molecules to return back to the patient, avoiding many complications associated with the therapeutic plasma exchange
o IA: There are different types of columns for IA.
§ IA with immobilized antibodies: are the most widely used in which column contains polyclonal sheep anti-human IgG antibodies and is effective in removing IgG antibodies. A different IA technique uses immobilized staphylococcal protein A. These Immunosorba columns, that contain staphylococcal protein A bound to sepharose is effective in removing IgG of different classes. Additionally, are able to induce a B cell apoptosis, so enhancing the immunosuppressive effect.
§ IA technique uses immobilized antigens and synthetic epitopes and is the most specific technique in removing only the undesirable antibodies
· Immunomodulation using IVIG: blocks the Fc receptor and has immunoregulatory properties
· blockage of complement system using eculizumab
· depleting of b-cell using splenectomy or rituximab
there is what is called an on-demand strategy in which the whole desensitization protocol is based according to the initial titer of anti-ABO antibodies in an attempt to reduce the costs
for example, at the Guy’s Hospital, Barnett et al adopted a tailored desensitization strategy in pairs with ABOi according to the initial anti-ABO antibody titer. With a titer of 8, only RTX was used; with a titer between 16 and 64, plasmapheresis was added to RTX therapy; and with a titer > 64, IA and RTX were used. No difference was observed regarding allograft and patient survival rates at 1 and 3 years or in the ABMR rates. These results highlight that a tailored desensitization strategy obtains good results with personalized therapy and lower costs.
Outcomes of ABOi kidney transplantation
Results need to be confirmed by large RCT but according to 2 meta-analyses of observational studies
· Both graft losses and mortality in transplants involving ABOi became equivalent to ABOc transplants at 8 years after transplantation
· transplants involving ABOi compared to those involving ABOc had a significantly higher mortality rate at 1, 3, and 5 years
· Coagulation disorders were also frequent in transplants involving ABOi. This complication is probably related to the modifications in the coagulation system induced by plasmapheresis or IA
· infectious disease specially Polyomavirus nephropathy was also more frequent in patients receiving RTX, as documented by several authors.
· Surgical complications in transplantations involving ABOi are similar to complications of standard transplants, with the exception of hemorrhages.
· ABMR is the first cause of graft loss in transplantations involving ABOi, However, it should be highlighted that both the antibody basal titer before desensitization and the post-transplantation titer has a low predictive value for ABMR
· ABOi transplants are more expensive than the ABOc transplants, however, they are less expensive than dialysis. in the case of ABOi transplant $ 65080 per transplant episode vs $32039 per transplant episode for an ABOc transplant.
CONCLUSION
the ABOi renal transplantation. Outcomes are almost similar to standard transplantations. The immunological barriers represented by the different ABO groups have been overcome and no major agreement on doses, types of immunosuppressive medications, and several questions still need to be answered like
· Apheresis technique used
· Role of rituximab
· Utility and role of IVIG
· Method to detect isoagglutinin’s quantity
· Type of immunosuppression
· Utility of post-transplantation apheresis
· Accommodation
· Role of protocol biopsies
· Principal complications
ABO incompatibility is approximately 30% of the immunological barrier for solid organ transplantation . Two different strategies are used to overcome these barriers: * desensitization of the recipient . *Paired Kidney Donation
Different protocols used for desensitization for ABO : A-Removal of circulating antibodies :
1- plasmapheresis :
Plasmapheresis :
Advantage : simple , cheaper
Disadvantages :
non-selectivity of removal of all immunoglobulins thus risk of infection is increased
hypocalcemia
coagulation factors deficiency.
20% of antibodies are removed within 1 session
The double filtration plasmapheresis: done by two plasma filters, and the second one allows smaller molecules to return back to the patient, avoiding many complications associated with the therapeutic plasma exchange.
2- Immunoadsorption :
Types of columns for IA.
IA with immobilized antibodies: . IA with immobilized antigens and synthetic epitopes and is the most specific technique in removing only the undesirable antibodies
B- Immunomodulation:
by using IVIG to
replace immunoglobulin lost during plasmapheresis
block FC receptors
complement inhibition
inhibit B/T-cell proliferation
increase B cells apoptosis
suppression of CD8 T-cell cytotoxicity.
C-B cell depletion :
Splenectomy:
replaced by using Rituximab ( medical spleenectomy)
Rituximab:
as it leads to depletion of B cells by binding to CD20 on these cells.
side effects: fever, chill, headache, and nausea
dose: 375mg/m2 1 month before KT
Different protocols used for desensitization :
in Europe :
IA is used more frequently and dose of Rituximab added 1 month before KT and one dose of IVIG 0.5 gm/kg one day before ABOi-KT
More recently, at the Guy’s Hospital :
ABO titer of 8 : only Rituximab was used
and of titer 16and 64: Rituximab + PP were used
and titer > 64: Rituximab + IAs were used
Accommodation : is defined as presence of antibodies but no harm and explained by change in the structure of antigens , specificity of the antibodies.
Clinical Outcomes in ABOI-KT :
Higher mortality rates in ABOi-KT more than in ABOc-KT at 1, 3, and 5 years
with no difference in mortality rates at 8 years
Complications: -surgical complications nearly same as ABOc-KT but increased risk of hemorrhage due to loss of coagulation factors during PP Infections: increase risk of infections of BK, CMV, HSV ABMR increases the risk of ABMR in ABOi-KT
Desensitization V.S KPD:
KPD is preferred on ABOi KT due to its low cost, no need for desensitization, and low immunological risk.
Nasrin Esfandiar
3 years ago
This article reviews different protocols and outcome of ABOi-KT as a solution for organ shortage and remaining on dialysis for a long time.
Immunological aspects: ABO antigens are glycoproteins express on RBC, endothelial and epithelial cells.
Recipients of blood group O, have high Ab titers to A and B antigens. So, they have higher risk of ABMR after TX. In addition to membrane-bind Ags, circulating antigens linked to Von willebrand factor exist in some patients and cause complement activation and C4d deposits. The persons with A2 subtype does not have circulating Ags.
Different desensitization protocols used over time:
1. Removal of circulating ABO antibodies:
This removal performed by DFPP or IA several days before TX to reduce anti-A/B Ab level to a level between 1:8 and 1:32.
DFPP is used by two filters and the second one permits return of vital molecules to the patient to decrease complications.
IA used different columns to remove selectively some humoral factors.
IA with a therasob column is effective in removing IgG Abs (by polyclonal sheep anti-human IgG Abs.
Immunosorba columns are effective in removing different classes of IgG and induce B cell apoptosis. Another one uses synthetic epitopes in addition to immobilized Ags and is the most specific technique.
2. Immunomodulation:
High doses of polyclonal IVIG is administered to the patient before TX to replace immunoglobulins lost and block the FC receptor.
3. B cell depletion:
To reduce production of isoagglutinin. This is done by splenectomy in the past and by using rituximab in recent years,
After 2 weeks, the transplanted kidney develops accommodation which means lack of rejection in spite of presence of ABO Abs.
Different protocols were evolved over time, by substitution of splenectomy by using rituximab and using different doses of rituximab, IVIG or IA according to patients isoagglutinin titers.
Clinical outcomes after ABOi-KT:
The results of studies with a low number of patients are generally good.
* There are two systematic review in this context.
The first one by ho et al, examined overall 4810 ABOi-KTs and showed that RTX and IA could have a superior efficacy but there were no RCTs comparing different protocols.
The second one was performed among 7098 ABOi-KTs.
Comparing with ABOC-KT, ABOi-KTs had higher mortality rates at 1,3 and 5 years. But graft losses and mortality in ABOi-KT became equivalent to ABOc-KT at 8 years post-TX. This was probably related to the side effect of high immunosuppression and severe bacterial or viral infections, showing need for reducing immunosuppression or desensitization therapy.
There are controversies in ABOi-KT:
1. Technique of apheresis:
Specific columns for IA are effective with fewer side effects but higher costs to reach a titer of 1:8 before TX.
What to do with patients with a low titer isoagglutinin?
2. Role of rituximab:
Although RTX replaced splenectomy, is it necessary in all patients? In recent meta-analysis only 35% of patients received RTX.
3. IVIG:
IVIG is used usually 500 mg/kg on the day before TX. But there are still different protocols.
4. Isoagglutinin quantification:
The best method is flux cytometry with high cost but tube and gel techniques are used, too.
5. Immunosuppression:
This is usually the same far standard TX. There are controversies about steroid – withdrawal.
6. Post TX apheresis:
Some authors do it in patients with isoagglutinin rebound.
7. Accommodation:
Low titer Abs, with low affinity and blockage of complement activation. Eculizumab, may facilitate accommodation or rescue therapy.
8. Protocol biopsies:
They usually show C4d in PTC with no sign of ABMR related to accommodation.
9. Complications:
Hemorrhages were associated with the number of IA. Infections complications related to immunosuppression and desensitization protocols were seen.
The incidence of ABMR was between 10%-30%.
KPD: KPD is a different way to overcome organ shortage. There are several models with growing suggestions for different models of single-center, regional, national or international strategies.
Zahid Nabi
3 years ago
The major hurdle in transplantation from living donor is that approximately 30% are immunologically incompatible because of the presence in the recipient of antibodies directed against the human leukocyte antigen system of the donor or because of the incompatibility of the ABO system.
This review article has tried to describe the different protocols to proceed with ABOi kidney transplant and it’s clinical outcome as well.
There are two principal strategies to overcome these barriers:
(1) To desensitize the recipient to remove the antibodies and modify the immunological status, allowing the transplant; and
(2) To exchange the organs between two or more pairs to exchange the organs between different donors.
Removal of circulating ABO antibodies
The removal of circulating ABO antibodies is obtained principally by plasmapheresis or immune-adsorption (IA). The aim of these strategies, principally applied several days before transplantation, is to reduce the circulating anti-A/B antibody levels to achieve titers between 1:8 and 1:32.
Immunomodulation
This technique consists in the administration of high doses of polyclonal intravenous immunoglobulin (IVIG) to the patient before transplantation. The aim is to replace the
patient’s immunoglobulins lost because of apheresis techniques. In addition, IVIG
blocks the Fc receptor and has immunoregulatory properties.
B cell depletion
B cells produce isoagglutinins, and their reduction is essential to obtain effective desensitization.
Intially splenectomy was considered a vital step for B cell depletion but now medical splenectomy with Rituximab has taken over as standard of care in different protocols of desensitization.
Guys hospital has adopted a tailored desensitization strategy in pairs with ABOi.
According to isoagglutinin titers Rituximab plus PP or IA was used . IA was added only for titer of 1:64 or above.
CLINICAL OUTCOMES AFTER RENAL TRANSPLANTATION INVOLVING
ABOI
In recent years, two systematic reviews and meta-analyses have been published and shed more light on the clinical outcomes of kidney transplantation involving ABOi.
Overall, transplants involving ABOi compared to those involving ABOc had a significantly higher mortality rates at 1, 3 and 5 years (odds ratio 2.17, 1.89 and 1.47, respectively; P < 0.0001).
Both graft losses and mortality in transplants involving ABOi became equivalent to ABOc transplants at 8 years after transplantation.
Coagulation disorders, Polyoma virus infection and severe bacterial or virus infection due to excessive immunosupression could be reason of increased mortality noted.
Major controversies encountered in ABOi renal transplant are
Apheresis techniques used
Role of Rituximab
Utility and role of IVIG
Method to detect isoagglutinin titers
Type of immunosupression
Utility of post transplant Apheresis
Concept of Accommodation and it’s exact role
Role of protocol biopsies
Principal complications
KPD
This could be one way of crossing immunological barrier however there are several points that needed clarification.KPD is cheaper but it’s availability in short time is big question
Mohammed Sobair
3 years ago
Current protocols and outcomes of ABO-incompatible kidney transplantation.
Approximately 30% of such transplantations are considered incompatible because of
HLA antigens of the donor or incompatibility of the ABO system between the donors and
recipient.
Two methods to overcome these barriers:
(1) To desensitize the recipient to remove the antibodies and modify the immunological
status.
(2) To exchange the organs between two or more pairs PKD.
Worldwide increase in the rate of kidney transplantations from living donors that involved
ABOi. This fact may be principally ascribed to four factors.
(1) knowledge of the diagnosis and treatment of ABMR has substantially improved.
(2) Japanese authors published excellent results in renal transplantations involving ABOi.
(3) Later, Johns Hopkins University and the Mayo Clinic in the United States documented
the possibility of performing such transplantation without splenectomy with the
administration of an anti-CD20 monoclonal antibody rituximab.
(4) Finally, Swedish authors developed a new technique that demonstrated outcomes in
renal transplantation involving ABOi that were similar to the outcomes of standard renal
transplantation.
TEHNIQUES OF ABO DESENSITIZATION AND DIFFERENT PROTOCOLS USED
OVERTIME
Removal of circulating ABO antibodies:
Plasmapheresis or immune-adsorption (IA).
The aim of these strategies:
Principally applied several days before transplantation, is to reduce the circulating anti-
A/B antibody levels to achieve titers between 1:8 and 1:32
The apheretic techniques:
The simpler, cheaper, but less effective technique has been the therapeutic plasma
exchange using highly permeable membranes.
The procedure eliminates approximately 20% of the antibodies by session. Additionally,
removes protective antibodies and coagulation factors.
The double filtration plasmapheresis is performed by two plasma filters, and the
second one allows smaller molecules to return back to the patient, avoiding many
complications associated with the therapeutic plasma exchange.
Types of columns for IA.
IA with immobilized antibodies: are the most widely used. A Therasorb column
contains polyclonal sheep anti-human IgG antibodies and is effective in removing IgG
antibodies.
Immobilized staphylococcal protein A.
These Immunosorbent columns, that contains staphylococcal protein A bound to
sepharose is effective in removing IgG of different classes. Additionally, are able to
induce a B cell apoptosis, so enhancing the immunosuppressive effect.
Another IA technique uses immobilized antigens and synthetic epitopes and is the
most specific technique in removing only the undesirable antibodies.
Immunomodulation:
Administration of high doses of polyclonal IVIG to the patient before transplantation.
Immunoglobulins lost because of apheresis techniques.
In addition, IVIG blocks the Fc receptor and has immunoregulatory properties.
B cell depletion:
Historically, splenectomy has been used principally in Japan for B cell depletion.
To date, RTX, a humanized monoclonal antibody that binds to CD20 expressed on the B
cell membrane, is the drug used to obtain B cell depletion.
Literature different protocols:
Initially plasmapheresis.
Technique of the IA, recently principally in Europe, plasmapheresis has been replaced
by the technique of the IA of isoagglutinins using specific protein A or anti-human Ig
columns.
Most all desensitization strategies used the administration of IVIG to improve
immunomodulation and the administration of RTX to avoid splenectomy.
More recently, at the Guy’s Hospital, Barnett etal adopted a tailored desensitization
strategy in pairs with ABOi. The different strategies were adopted according to the initial
anti-ABO antibody titer with a titer of 8, only RTX was used;
With a titer between 16 and 64, plasmapheresis was added to RTX therapy;
And with a titer > 64, IA and RTX were used.
CLINICAL OUTCOMES AFTER RENAL TRANSPLANTATION INVOLVING ABO:
Overall, transplants involving ABOi compared to those involving ABOc had a significantly
higher mortality rates at 1, 3 and 5 years.
Both graft losses and mortality in transplants involving ABOi became equivalent to ABOc
transplants at 8 years after transplantation.
Excess immunosuppression is the cause of severe bacterial or viral infections.
Coagulation disorders were also frequent.
OPEN CONTROVERSIES IN KIDNEY TRANSPLANTATION INVOLVING ABO:
Main controversies .
Apheresis technique.
Used Role of rituximab .
Utility and role of IVIG .
Method to detect isoagglutinins .
Quantity Type of immunosuppression.
Utility of post transplantation apheresis.
Accommodation Role of protocol biopsies.
Principal complications.
KPD:
The simplest model of the KPD is the two-way, in which two pairs of donors and
recipients with ABOi exchange the kidneys, thereby resolving the incompatibility.
The model may also include a higher numbers of pairs realizing the KPD at three-way,
four-way, and so on.
A further increase in kidney exchanges was realized by the domino KPD, which start
from an altruistic donor and finish with the donation of a kidney to a recipient on the
waiting list.
A variant of domino KPD is the Never Ending Altruistic chain, which allows a higher
number of recipients to be transplanted by the use of bridge donors.
CONCLUSION:
To date, the ABOi renal transplantation is possible because of the reconditioning
strategies available. Many reports document outcomes similar to the standard
transplantations.
ABOi transplants are more expensive than the ABOc transplants, however they are less
expensive than dialysis.
Wael Jebur
3 years ago
Renal transplantation is considered the treatment modality of choice for ESKD patients.
Nevertheless, HLA and ABO incompatibility challenge undermine this process. Strategies to overcome the incompatibility barriers continued to develop. As this incompatibility, considered the main risk factor for development of AMR which portend the risk of premature loss of the allograft.
Strategies for desensitization developed over time to overcome this risk, include:
1] Removal of ABO antibodies:
a- Aiming at lowering the antibody titer to less than 1/32 at the time of transplantation.
b-Performed pre-transplantation to optimize immunologic tolerance and minimize hyperacute rejection risk.
c-Include PP where in highly permeable plasma filter, used to remove the antibodies ,with drawback of removing the protective antibodies and coagulation factors, carrying a higher risk of bleeding.
d-DFPP, uses two plasma filters ,permitting the return of smaller molecules to the patients, reducing the risk of bleeding.
e-IA : is the latest technology used for the clearance of circulating antibodies. Its the most specific procedure to remove the undesired antibodies.
f-IA main draw back is highly expensive procedure.
g- The post operative removal of antibodies is not routinely performed, but it depends on antibody rebound reflected as post transplant antibody titer on-demand strategy. Rebound will be critical only for the first 2 weeks post transplant after which the risk of rejection is minimal even with rebound and activation of complement system, a phenomena called accommodation.
2] Immunomodulation:
High dose of polyclonal immunoglobulins [IVIG] is administered preoperatively to replenish the immunoglobulines lost by PP. Its blocking the FC receptors in different cell types. Furthermore it has several modulatory functions as well.
3] B-lymphocyte depletion.
As the B-lymphocytes are the source of isoagglutinins, it was mandatory to be depleted in order to precondition the patient with desensitization for ABOi transplantation.
Historically splenectomy was the modality of choice. Replaced efficiently by Rituximab {RTX}.
Protocols for desensitization:
1] PP, DFPP and IA, IVIG and RTX:
RTX 30 days prior to Transplantation 375 mg/mm, IA until Isagglutinin titer less than 32%, and IVIG 0.5 g/kg one day before transplantation.
2] Due to high risk of post transplant infectious complication, different protocol adopted to minimize immunosuppression. like considering IA and IVIG only protocol.
3} In Guys hospital , depending on Antibody titer, strategy was set as follow:
a-Titer less than 8%, only one dose of RTX.
b-16-64 % PP and RTX
c-more than 64% IA and RTX.
Evaluating outcomes after transplantation:
2 large scale meta analysis were, conducted to evaluate the outcome of ABOi renal transplantation, showed different results, with good outcome in the first in Lo et al study and poor out come with Florin G scurt et al
The vast majorities of controversies revolve around the desensitization strategy .
Main debates encountered :
apheresis techniques
RTX
IVIG
Post Transplant pheresis.
Detection of isoagglutinin titer.
accommodation.
protocol biopsy
type of immunosuppression.
PKD:
Offer safer and more feasible strategy to overcome the ABOi barrier. In USA PKD is growing and desensitization strategy is dropping.
Shereen Yousef
3 years ago
Renal transplantation is the best therapy for ESRD patients
living kidey donor is the best option but many of recipients on the waiting list are sensitized and its difficult to find matched doner for them.
Also waiting for deceased donor might be for many years due to shortage of organs
two principal strategies to overcome these barriers: (1) desensitize to remove the antibodies (2) Paired kidney exchange programmes.
ABOI-KT helped to increase donor pool.
▪︎IMMUNOLOGICAL ASPECTS
ABO system antigens are expressed on RBCs, epithelial ,endothelial cells,collecting and distal tubules and on the vascular endothelial cells.
Bl.group A has anti B antibodies, while Bl.group B has anti A antigens antibodies
O individuals have higher antibody titers to both the A and B antigens
So they remain for longer time on waiting list and have a higher incidence of ABMR.
There are also circulating epitopes A and B, both are soluble and linked to von Willebrand factor exist in some patients,These antigens, when free, are responsible for ABMR.
better results in transplantation involving ABOi are obtained when transplanting kidneys from A2 donors to O recipients.
The A2 subtype does not have circulating antigens linked to von Willebrand factor.
▪︎ DESENSITIZATION AND DIFFERENT PROTOCOLS USED OVER TIME
Combination of different strategies are applied
*Removal of circulating ABO antibodies
The aim is reduction of isoagglutinin levels to achieve titers between 1:8 and 1:32.
•plasmapheresis; simple and cheape,and less effective it removes 20% of the antibodies by session also removes protective antibodies and coagulation factors.
•The double filtration plasmapheresis avoids many complications associated of plasma exchange.
The number of apheresis session is variable till reaching a titer of 1:8 before transplantation.
•Immune-adsorption
IA with immobilized antibodies: are the most widely used
It’s effective in removing IgG of different classes and induces B cell apoptosis, so enhancing the immunosuppressive effect.
Another IA technique uses immobilized antigens and synthetic epitopes and is the most specific technique in removing only the undesirable antibodies.
•Intravenous immunoglobulin (IVIG) given to
patient before transplantation after plasmapheresis ,IVIG blocks the Fc receptor and has immunoregulatory properties.
It is givin in a dose 500 mg IVIG/kg body weight 1 day before transplantation or divided on 4 d and 1 d before transplantation.
•B cell depletion
B cells produce isoagglutinins, and their reduction is essential to obtain effective desensitization.
Historically, splenectomy has been used replaced now by anti CD20 monoclonal antibody rituximab .
RTX reduces the risk of isoagglutin rebound, the risk of ABMR and the risk of chronic rejection.
•Accommodation:a phenomenon that occurs in the first 2 weeks post transplantation due to exposure to low ABO antibody titer allows the graft to resist complement-mediated damage.
•Different protocols for desensitization
in Europe, plasmapheresis was replaced by the technique of the IA of isoagglutinins using specific protein A or anti-human Ig columns due to its high capacity to induce ABO agglutinin removal with high biocompatibility and without complement activation.
all desensitization strategies used the administration of IVIG +Rituximab.
By 2007, Genberg et al compared with 27 transplants between ABO compatible (ABOc) pairs. Incompatible recipients were treated with IA and a single dose of RTX (375 mg/m2 of body surface) 30 d before transplantation. The day before transplantation, the patients were given IVIG at a dose of 0.5/kg body weight.
There was no significant difference in patient and graft survival rates or in the rejection episode rates. The patient follow-up was as long as 3 years, and at 3 years, the same estimated glomerular filtration rate was observed in both groups.
Later they observed a harmful antibody rebound after the interruption of IA and suggested that patients should be carefully monitored both before and after transplantation.
More recently, at the Guy’s Hospital, tailored desensitization strategy in pairs with ABOi. According to initial anti-ABO antibody titer so With a titer of 8, only RTX was used; with a titer between 16 and 64, plasmapheresis was added to RTX therapy; and with a titer > 64, IA and RTX were used.
using this strategy, the results were compared with ABOc transplants. No difference in allograft and patient survival rates at 1 and 3 years or in the ABMR rates.
•Immunosuppression
immunosuppression in ABOi-KT is similar to that used for standard transplantation. The basal immunosuppression begins together with the desensitization.
Post transplantation apheresis is done with impaired graft function.
•Role of protocol biopsies
protocol biopsy at 1 and 2 years, C4d in peritubular capillaries was found with no sign of ABMR or transplant glomerulopathy
It is related to accommodation if not associated with abnormal graft function.
•Complications
-Surgical complications are the same to standard transplants.
– Hemorrhages are more common than standard transplantation.
The hemorrhages were significantly associated with the number of IA sessions.
-infectiouns related to the intensity of desensitization strategies.
-ABMR is the first cause of graft loss in transplantations involving ABOi. The risk for ABMR is related to the isoagglutinin level at transplantation and to the presence of anti-HLA antibodies.
•KPD; kidney paired donation is a good strategy to help 2 or more incompatible pairs to find more matched donor so avoid heavy immunosuppression with its complications.
The simplest model of the KPD is the two-way, it may expand to involve a higher numbers of pairs realizing the KPD at three-way, four-way, and so on.
•CONCLUSION
-ABOi renal transplantation is no more contraindicated and outcomes similar to the standard transplantations.
-ABOi transplants are more expensive than the ABOc transplants, however they are less expensive than dialysis.
– wider extension of KPD programmes will help to perform more compatible transplantation.
mohamed hefzy
3 years ago
Current protocols and outcomes of ABO-incompatible kidney transplantation
Renal transplantation is considered the best therapy for patients affected by end-stage renal disease. However, approximately 30% of such transplantations are considered incompatible from the immunological point of view either because of the presence in the recipient of antibodies directed against the human leukocyte antigen (HLA) antigens of the donor or because of the incompatibility of the ABO system between the donor and recipient or because of both . There are two strategies to overcome these barriers: (1) To desensitize the recipient to remove the antibodies . (2) To exchange the organs between two or more pairs to exchange the organs between different donors.
IMMUNOLOGICAL ASPECTS
Indeed, better results in transplantation involving ABOi are obtained when transplanting kidneys from A2 donors to O recipients. The A2 subtype does not have circulating antigens linked to von Willebrand factor . The reaction of isoagglutinins with the antigens of the ABO group induces complement activation, as documented by the presence of C4d .In addition to its relation with the development of ABMR, the presence of C4d on the tissues may also be associated with the development of chronic rejection
DEVELOPMENT OF THE PRACTICE OF KIDNEY TRANSPLANTATION IN ABO- INCOMPATIBLE PAIRS For a long time, ABOi has been considered an absolute contraindication to kidney transplantation. For the first time, Brynger et al[9] reported the clinical outcomes of 21 renal transplantations from A2 donors to O recipients. Since then, several authors have tried to perform kidney transplantations in pairs with ABOi[10-13] . Principally after 1998, there was a worldwide increase in the rate of kidney transplantations from living donors that involved ABOi. This fact may be principally ascribed to four factors. (1) Since 1998, our knowledge of the diagnosis and treatment of ABMR has substantially improved. (2) By the beginning of 2000, Japanese authors published excellent results in renal transplantations involving ABOi[14] , although the main limitation of the Japanese strategy was the splenectomy associated with their pretransplantation protocol. (3) Later, Johns Hopkins University and the Mayo Clinic in the United States documented the possibility of performing such transplantation without splenectomy with the administration of an anti-CD20 monoclonal antibody (rituximab [RTX])[7,15] . (4) Finally, Swedish authors developed a new technique that demonstrated outcomes in renal transplantation involving ABOi that were similar to the outcomes of standard renal transplantation
TECHNIQUES OF ABO DESENSITIZATION AND DIFFERENT PROTOCOLS USED OVER TIME
Removal of circulating ABO antibodies
Immunomodulation
B cell depletion
CLINICAL OUTCOMES AFTER RENAL TRANSPLANTATION INVOLVING ABOI
Overall, transplants involving ABOi compared to those involving ABOc had a significantly higher mortality rates at 1, 3 and 5 years . Both graft losses and mortality in transplants involving ABOi became equivalent to ABOc transplants at 8 years after transplantation.
The higher mortality rate is probably a consequence of the high immunosuppression related to the therapy
Coagulation disorders were also frequent in transplant involving ABOi.
Polyoma virus nephropathy was also more frequent in patients receiving RTX
OPEN CONTROVERSIES IN KIDNEY TRANSPLANTATION INVOLVING ABOI
desensitization aims to modify the immunological reaction in different ways:
(1) Antibody reduction by plasmapheresis or IA.
(2) Inhibition of antibody production by splenectomy (old system) or by RTX.
(3) Pleiotropic action of IVIG.
(4) Complement inhibition by Eculizumab .
Main controversies Apheresis technique used Role of rituximab Utility and role of IVIG Method to detect isoagglutinins quantity Type of immunosuppression Utility of posttransplantation apheresis Accommodation Role of protocol biopsies Principal complications
KPD KPD programs have several points that yet need to be better clarified. The principals are as follows:
Transportation of kidneys vs donor travel
Simultaneous vs no simultaneous exchanges
Closed chains vs open chains
Reem Younis
3 years ago
-For ESRD patients, to avoid a long time on dialysis, transplantation from living donor is the best option. However, approximately 30% ofsuch transplantations are considered incompatible from the immunological point of view either because of the presence in the recipient of antibodies directed against the HLA antigens of the donor or because of the incompatibility of the ABO system between the donor and recipient or because of both.
-There are two principal strategies to overcome these barriers:
(1) To desensitize the recipient to remove the antibodies and modify the immunological status, allowing the transplant.
(2) To exchange the organs between two or more pairs to exchange the
organs between different donors.
– Better results in transplantation involving ABOi are obtained when transplanting kidneys from A2 donors to O recipients. The A2 subtype does not have circulating antigens linked to the von Willebrand factor.
-The reaction of isoagglutinins with the antigens of the ABO group induces
complement activation, as documented by the presence of C4d.
– In addition to its relation to the development of ABMR, the presence of C4d on the tissues may also be associated with the development of chronic rejection.
-The most frequent protocols applied to obtain desensitization in pairs with ABOi are a mixture of the following strategies.
1.Removal of circulating ABO antibodies:
The removal of circulating ABO antibodies is obtained principally by plasmapheresis or immune-adsorption (IA). The aim of these strategies principally applied several days before transplantation, is to reduce the circulating anti-A/B antibody levels to achieve titers between 1:8 and 1:32.
2.Immunomodulation
This technique consists in the administration of high doses of polyclonal intravenous immunoglobulin (IVIG) to the patient before transplantation. The aim is to replace thepatient’s immunoglobulins lost because of apheresis techniques. In addition, IVIG blocks the Fc receptor and has immunoregulatory properties.
3 .B cell depletion
B cells produce isoagglutinins, and their reduction is essential to obtain effective desensitization.
Historically, splenectomy has been used principally in Japan for B cell depletion. To date, RTX, a humanized monoclonal antibody that binds to CD20 expressed on the B cell membrane, is the drug used to obtain B cell depletion.
Independent of which strategy is used, the common aim is to reduce the agglutinin titer to a predetermined level.
-The phenomenon of lack of rejection in the presence of circulating ABO antibodiescomplement activating is known as accommodation and it is also
responsible for kidney protection over a long period of time.
-The most frequently used technique was the removal of circulating anti-ABO
antibodies by plasmapheresis .
More recently, principally in Europe, plasmapheresis has been replaced by
the technique of the IA of isoagglutinins using specific protein A or anti-human Ig
columns . The main advantages of this technique are to its high capacity to induce
ABO agglutinin removal with high biocompatibility and without complement
activation.
-Almost all desensitization strategies used the administration of IVIG to improve immunomodulation and the administration of RTX to avoid splenectomy.
-Attempts to reduce the RTX doses were made, as well as attempts to completely
omit RTX administration.
– Tailored desensitization strategy obtains good results with personalized therapy and lower costs.
-The results obtained after renal transplantation involving ABOi are generally good and overlap with the results obtained in ABOc renal transplantation.
-Overall, transplants involving ABOi compared to those involving ABOc had a
significantly higher mortality rates at 1, 3 and 5 years .
-Both graft losses and mortality in transplants involving ABOi became equivalent to ABOc transplants at 8 years after transplantation.
-The higher mortality rate is probably a consequence of the high immunosuppression related to the therapy. Coagulation disorders were also frequent in transplant involving ABOi.
-The use of a high dose of RTX or the use of other immunosuppressants to reach a higher desensitization was also associated with a higher mortality rate due to infectious disease.
-Polyoma virus nephropathy was also more frequent in patients receiving RTX, as
documented by several authors .
-Surgical complications in transplantations involving ABOi are similar to complications of standard transplants, except for hemorrhages. Hemorrhages are likely to be ascribed to the apheresis treatment.
-The hemorrhages were significantly associated with the number of IA sessions.
-ABMR is the first cause of graft loss in transplantations involving ABOi. The risk
for ABMR is related to the isoagglutinin level at transplantation and the presence of anti-HLA antibodies.The incidence of ABMR ranges between 10% and 30%.It principally occurs in the early post-transplantation, usually in the first 2 wk. KPD
-The simplest model of the KPD is two-way, in which two pairs of donors and
recipients with ABOi exchange the kidneys, thereby resolving the incompatibility.
-With the increasing number of KPD programs, it has been possible to achieve a
global kidney exchange.
-A further increase in kidney exchanges was realized by the domino KPD, which
start from an altruistic donor and finish with the donation of a kidney to a recipient on the waiting list. A variant of domino KPD is the Never Ending Altruistic chain, which allows a higher number of recipients to be transplanted by the use of bridge donors .
Mohamed Ghanem
3 years ago
Antigens and antibodies of ABO : Antigens are glycoproteins found on RBCs, platelets, endothelial cells, and renal tubules.
anti A/B antibodies formed against these antigens with blood group O have both types of antibodies anti-A and anti B antibodies while blood group AB has no antibodies. Different protocols used for desensitization for ABO : A-Removal of circulating antibodies :
1- plasmapheresis :
Plasmapheresis with the exchange of plasma with other colloid plasma or albumin
With side effects of non-selectivity of removal of all immunoglobulins and increased risk of infection, hypocalcemia, and coagulation factors deficiency.
2- The double filtration plasmapheresis :
done by 2 plasma filters with fewer complications of plasmapheresis
3-IA :
Removing of IgG antibodies with two subtypes selective and non-selective
Selective only remove undesirable antibodies B- Immunomodulation:
uses of high doses of IVIG to replace immunoglobulin lost during plasmapheresis
and block FC receptors, complement inhibition, inhibit B/T-cell proliferation, increase B cells apoptosis, and suppression of CD8 T-cell cytotoxicity. C-B cell depletion : Splenectomy: the concept dependant that the spleen is the reservoir for both B cells and plasma cells
Splenectomy has been largely abandoned and replaced by Rituximab
due to increased risk of sepsis with encapsulated organisms, pancreatic leakage, and portal vein thrombosis.
Rituximab:
as it leads to depletion of B cells by binding to CD20 on these cells.
side effects: fever, chill, headache, and nausea
dose: 375mg/m2 1 month before KT
Different protocols used for desensitization : in Europe IA is used more frequently than PP as high selectivity, capacity for removal of A/B antibodies and to avoid complications resulting from PP
and dose of Rituximab added 1 month before KT and one dose of IVIG 0.5 gm/kg one day before ABOi-KT
More recently, at the Guy’s Hospital :
ABO titer of 8 or less: only Rituximab was used
and of titer 16and 64: Rituximab + PP were used
and titer > 64: Rituximab + IAs were used Immunosuppression :
immunosuppression in kidney transplantation with ABOi-KT is the same used in ABOc-KT but high risk of ABMR during steroid withdrawal. Post-transplantation apheresis: indicated for patients presented with allograft dysfunction with the presence of a high titer of anti-A/B antibodies. Accommodation : despite an increase of Incompatible antibodies post-transplant, these make no harm due to the Accommodation phenomenon as based on less avidity, specificity of antibodies, and change of structure of antigens. Clinical Outcomes in ABOI-KT :
Higher mortality rates in ABOi-KT more than in ABOc-KT at 1, 3, and 5 years
with no difference in mortality rates at 8 years Complications: surgical complications were the same as ABOc-KT but increased risk of hemorrhage due to loss of coagulation factors during PP Infections: increase risk of infections of BK, CMV, HSV, sepsis, and UTI. ABMR increases the risk of ABMR in ABOi-KT( ranges between 10% and 30%)
Desensitization V.S KPD:
KPD will be a good choice if available due to its low cost, no need for desensitization, and low immunological risk. Conclusion :
ABOi-KT has a high cost than the ABOc-KT, however, they are less expensive than dialysis.
the ABOi kidney transplantation became available due to advances in desensitization protocols used for the removal of A/B antibodies
KPD should be increased to increase the number of transplants
Ahmed Abd El Razek
3 years ago
INTRODUCTION
The presence in the recipient of antibodies directed against the human leukocyte antigen (HLA) antigens of the donor or because of the incompatibility of the ABO system between the donor and recipient or because of both makes transplantation a hard job. Better options included desensitization and kidney paired donation programs.
IMMUNOLOGICAL ASPECTS
At the renal level, glycoproteins are expressed on the collecting and distal tubules and on the vascular endothelial cells. The intensity of antigen expression on the tissues is also related to the acute rejection rate in patients with low isoagglutinin levels in the blood.
Group O individuals have higher antibody titers to both the A and B antigens. So, they have a higher incidence of
Antibody-mediated rejection (ABMR) after transplantation.
The reaction of isoagglutinins with the antigens of the ABO group induces complement activation, as documented by the presence of C4d.
TECHNIQUES OF ABO DESENSITIZATION Removal of circulating ABO antibodies
Principally by plasmapheresis or immune-adsorption (IA) to achieve titers between 1:8 and 1:32.
Immunomodulation
Using high doses of polyclonal intravenous immunoglobulin (IVIG) to the patient before transplantation. It blocks the Fc receptor and has immunoregulatory properties.
B cell depletion
RTX, a humanized monoclonal antibody that binds to CD20 expressed on the B cell membrane is now the drug of choice.
The transplanted kidney develops in approximately 2 wk. the capacity to resist complement-mediated damage. The phenomenon of lack of rejection in the presence of circulating ABO antibodies complement activating is known as accommodation.
A tailored desensitization strategy obtains good results with personalized therapy and lower costs.
CLINICAL OUTCOMES AFTER RENAL TRANSPLANTATION INVOLVING ABOI
Transplants involving ABOi compared to those involving ABOc had a significantly higher mortality rates at 1, 3 and 5 years.
Both graft losses and mortality in transplants involving ABOi became equivalent to ABOc transplants at 8 years after transplantation.
The higher mortality rate is probably a consequence of the high immunosuppression related to the therapy.
Coagulation disorders were also frequent in transplant involving ABOi that were related to the modifications in the coagulation system induced by plasmapheresis or IA.
The use of a high dose of RTX or the use of other immunosuppressants to reach a higher desensitization was also associated with a higher mortality rate due to infectious disease.
Polyoma virus nephropathy was also more frequent in patients receiving RTX.
Immunosuppression
The basal immunosuppression begins together with the desensitization.
Post-transplantation apheresis
It is reserved for patients who present abnormalities of graft function together with isoagglutinin rebound.
Accommodation
In the presence of circulating antibodies and antigens on the graft cell surface, the graft itself may not be rejected.
Accommodation in renal transplantation involving ABOi has been defined as the presence of circulating isoagglutinins and antigens on the graft cells with normal renal function and normal histology. The mechanism is thought to be due to the presence of a low titer of antibodies, with low affinity and with the blockage of complement activation.
Under these conditions, endothelial cells develop a phenotypic change according to which they become resistant to antibody damage. Eculizumab, a monoclonal antibody against C5, may facilitate accommodation. It may represent a rescue therapy in the case of severe ABMR.
Role of protocol biopsies
C4d in peritubular capillaries was found with no sign of ABMR or transplant glomerulopathy. It is related to accommodation.
Complications
Surgical complications in transplantations involving ABOi are similar to complications of standard transplants, with the exception of hemorrhages related to the apheresis treatments.
ABMR principally occurs in the early post-transplantation, usually in the first 2 wk.
CONCLUSION
Programs of paired kidney donation are worldwide need to be verified and validated.
Jamila Elamouri
3 years ago
Current protocols and outcomes of ABO-incompatible kidney transplantation
Kidney transplantation is the best treatment for ESRD patients. To date, many challenges facing this treatment in addition to cadaveric donor shortage. Contributing to the increase in the number of patients on the waiting list. Immunological reactivity represents one of these challenges. Transplantation from the living donor is the best option to avoid a long time on dialysis. However, about 30% of these transplantations are immunologically incompatible, either due to the presence of DSA in the recipient serum that is directed against the human leukocyte antigen (HLA) antigens of the donor or due to the incompatibility of the ABO system between the donor and recipient or because of both. To overcome these barriers there are two strategies: (1) desensitization of the recipient to remove the DSA to allow transplantation or (2) paired kidney exchange strategy. Immunological Aspects
The ABO system consists of glycoprotein antigen expressed on the erythrocyte membrane, epithelial and endothelial cells. in the kidney, this antigen is expressed on the collecting and distal tubules and on the vascular endothelial cells. the intensity of them is related to the acute rejection.
The ABO groups are A, B, AB, and O types. The antibodies against ABO antigens are formed against the antigen that is not native to the host. Group O individuals have higher antibody titers to both the A and B antigens, consequently, they have a higher incidence of ABMR after transplantation. The ABO system antigens have two forms; membrane-linked antigens and circulating epitopes A and B soluble and linked to Von Willebrand factor exist in some patients. These antigens when free, can cause ABMR. For ABOi transplantation better results were obtained between A2 donors and O recipients. As A2 subtype does not have circulating antigens linked to Von Willebrand factors. The reaction of isoagglutinins with the antigens of the ABO group causes complement activation, with C4d deposition on the tissues indicating ABMR. Development of the practice of kidney transplantation in ABO-Incompatible pairs:
Brynger et al, were the first to report ABOi transplantation between A2 donors and O recipients.
Since 1998; the ABOi kidney transplantation has been increased worldwide. As our knowledge of the diagnosis and treatment of ABMR improved as well different successful protocols exist. Like Japanese authors’ strategy although splenectomy was the main limitation of it. Johns Hopkins University and Mayo clinic strategy that includes the anti0CD20 monoclonal antibody (rituximab instead of splenectomy). Swedish authors also published new techniques with a good outcomes. TECHNIQUES OF ABO DESENSITIZATION AND DIFFERENT PROTOCOLS USED OVER TIME Most protocols are mixture of the following strategies: Removal of circulating ABO antibodies
This is done by plasmapheresis or immune-adsorption (IA). This therapy is carried out several days before transplantation. aimed to reduce circulating anti-A/-B antibody levels to below 1:8 and 1:32
The therapeutic plasma exchange using highly permeable membranes allows elimination of 20% of the circulating antibodies by session, but it also remove other proteins like protective antibodies and coagulation factors. This is evoluted to more advanced technique using double filtration membranes, in which the second membrane allows smaller molecules to return back to the patient, thus avoiding many complications of the previous therapeutic plasma exchange. For immune adsorption there are different types of columns:
1- IA with immobilized antibodies:
It is the most widely used method. A Therasorb column contains:
a- polyclonal sheep anti-human IgG antibodies, remove IgG Abs effectively.
b- Staphylococcal protein A bound to sepharose, is effectively remove IgG of different classes. In addition, they are capable of inducing a B cell apoptosis, so enhancing the immunosuppression.
2- IA technique uses immobilized antigens and synthetic epitopes:
This is more specific, removing only the undesirable antibodies. Immunomodulation
It consists of the administration of high doses of polyclonal IVIG before transplantation. to replace the immunoglobulin lost by plasmapheresis, also it blocks the FC receptor and has immunoregulatory properties. B cell depletion
The isoagglutinin are produced by B cells, so depletion of B cell is an essential step in the desensitization. Historically; this was done by splenectomy in Japanese protocol. Newly, rituximab, anti-CD20 monoclonal antibody used to obtain B cell depletion.
All methods aim to reduce ABO antibody titer. The transplanted kidney when exposed to a low titer of circulating antibodies, acquires in 2 weeks the capacity to resist complement-mediated damage. A phenomenon is called accommodation. Lack of rejection in the presence of circulating ABO antibodies complement activation.
Almost all desensitization strategies use the administration of IVIG to improve immunomodulation and the administration of rituximab to avoid splenectomy. CLINICAL OUTCOMES AFTER RENAL TRANSPLANTATION INVOLVING ABOI
The ABOi renal transplantation outcomes are generally good and overlap with ABOc renal transplantation. although these results were obtained from studies including a small number of patients and they were unable to compare different therapies. Further research should be conducted on which pre-transplantation therapies should be adopted.
Overall, the evidence of the benefits of different preconditioning therapies is low.
A new wider systemic review study including a large number of patients shows that ABOi transplants had a significantly higher mortality rate at 1, 3, and 5 years compared to those involving ABOc. While at 8 years both graft losses and mortality in ABOi transplant group become equivalent to ABOc transplants.
The higher mortality rate in ABOi transplants is probably related to the side effects of high immunosuppression that increase the incidence of infection. Polyomavirus nephropathy was more prevalent in the rituximab group. OPEN CONTROVERSIES IN KIDNEY TRANSPLANTATION INVOLVING ABOI
ABOi transplants still carry many controversies. The majority of these controversies involve the strategies of desensitization. That involves plasmapheresis, splenectomy (old way), or rituximab, pleiotropic action of IVIG, complement inhibition by eculizumab. Technique of apheresis
The number of plasmapheresis differs depending on the basal levels of isoagglutinins and the centre experience. Role of Rituximab (RTX)
Its sued allowed avoidance of splenectomy. The use of rituximab reduces the risk of isoagglutinin rebound and the risk of ABMR as well reduces the chronic rejection. It is given 1 month before transplantation. IVIG
It acts through (1) blockage of Fc receptor on the leukocyte membrane, (2) inhibition of the complement activation, and (3) inhibition of the circulating antibodies against HLA. It reduces antibody rebound after transplantation and ABMR risk.
Isoagglutinin quantification
Isoagglutinin titer determination is necessary to decide on the immunosuppression and in particular the apheresis technique to be used. Immunosuppression
The immunosuppression in ABOi transplantation is similar to that used for standard transplantation. overall, patients receiving ABOi transplantation are not allowed to reduce immunosuppression. Post-transplantation apheresis
Patients who develop graft function abnormality together with isoagglutinin rebound receive apheresis treatment. Accommodation
Phenomenon involves the presence of circulating antibodies and antigens on the graft cell surface, in the presence of normal graft function and histology (i.e no rejected). This phenomenon seems to be due to low titer antibodies, low affinity and complement blockade. By this, the endothelial cells develop resistance to antibody damage. The accommodation can be facilitated by reduction of the isoagglutinin titer by rituximab, IA specific columns, and complement activation blockade.
Eculizumab is a monoclonal antibody against C5, facilitates accommodation, and allows ABOI transplantation. it may be used as rescue therapy in severe ABMR. Role of protocol biopsies
The presence of C4d in protocol biopsies of ABOi renal transplants seems to be related to accommodation when found in the absence of clinical or histological abnormalities. Complications:
Surgical complications in ABOi transplantations are similar to standard transplants. Haemorrhages are common that are likely to be related to the apheresis treatment. Infectious complications were significantly related to the number of IA sessions and the intensity of desensitization strategies.
ABMR is the first cause of graft loss and it is related to the isoagglutinin level at transplantation and to the presence of anti-HLA antibodies. Kidney Paired Donation
Develop to overcome the immunologic barrier to transplantation. it ranges from the simplest model of the KPD that involves two pairs of donors and recipients to domino KPD which starts with an altruistic donor and finishes with the donation of a kidney to a recipient on the waiting list. MAKING A CHOICE BETWEEN DESENSITIZATION AND KPD
It remained to be answered by the availability of KPD in a short time. That depends on the organization. KPD is generally cheaper than desensitization. Overall, the KPD is growing, while the desensitization strategy is dropping. Conclusion
The ABOi renal transplantation is possible with the use of a desensitization strategy by which the immunological barrier of different ABO groups has been overcome.
This success is attributed to the accommodation as well to the achievement of some humoral tolerance. No standardized apheresis protocol has been agreed to. And researches are in needs to answer the question in regards of best desensitization protocols, the role of rituximab, the significance of C4d in the graft with normal function and the accommodation phenomenon role.
ABOi expansive therapy as compared to ABOc transplantation and KPD represents an option to decrease this cost but it needs good organization at the national and international levels to increase the probability to find a suitable donor. Worldwide, KPD has substantially increased, therefore, increasing the number of transplants. A wide national registry for PKD would be used instead of small registries to increase transplants.
Batool Butt
3 years ago
Transplantation is the treatment of choice for ESRD patients and living donor transplant is better alternative to compensate for shortage of deceased donor pool patients with ESRD, but around 30% of patients are sensitized –PKD program and desensitization will help to solve this issue. IMMUNOLOGICAL ASPECTS
Blood group antigens are presented on RBCS , endothelial cells and renal tubular epithelial cells in certain circumstances, they include A, B, AB, O . Patient with blood group A has anti B antibodies, while those with blood group B has anti -B antibodies.Individuals with blood group O has no antibodies so they are universal donors. However, patients with blood group AB are universal recipient. Blood group A has 2 subtypes: A1 (80 %) and A2 (20%, less immunogenic). Recipients with anti-A sera ( those with blood group B, O) can receive kidneys from donors with blood group A2 if anti-A sera is low. Individuals with blood group A2 can serve as universal donors but only if the titer of antibodies is low TECHNIQUES OF ABO DESENSITIZATION AND DIFFERENT PROTOCOLS USED OVER TIME B cell depletion is done by Rituximab which was done by splenectomy in the past. Some protocols do not used rituximab at all if patient had reached an anti-A/B antibody titer of less than 1:32 with good graft survival. An absence of detectable splenic B cells occur after rituximab administration,but plasma cells remain as they lack CD20 receptors. The specific dose of rituximabis not clear and is given four weeks prior to the scheduled transplant surgery date. Antibodies removal Removal of circulating ABO antibodies
Plasmapheresis removes 20% of antibodies in a session along with coagulation factors leading to bleeding tendency and remove all IgG with higher risk of infection and sepsis.
Double filtration plasmapheresis uses second filter which allows return of essential components to the blood and has fewer complications.
IA selectively eliminates humoral factors using immobilised Ab or immobilised staph protein A or immobilized antigens and synthetic epitopes with the least side effects (produce 2-4 fold titer reduction per session), but more expensive than plasmapheresis and not widely available.
Isoagglutinin titer is assessed 2 weeks before transplantation. The goal is to achieve isoagglutinin titer of ≤1:8 Immunomodulation
Using IVIG having immunomodulatory role and acts as an immunomodulator by blocking Fc receptors , so it prevents the rebound increase in antibody by plasma cells, moreover IVIG aid in the replacement of immunoglobulins that are removed during PE or IA. IVIG is usually given after plasmapharesis, but one regimen is to give 0.5 gm/kg in 1 dose the day before transplantation or in 2 doses 4 and 1 day before transplantation
There is no standard protocol for desensitization prior to transplantation, but in general, we can give rituximab 2 weeks prior to transplantation and do plasmapheresis 4 sessions 1 week before operation and continue it for another 3-4 sessions post transplant, induction using either basiliximab or ATG according to other risk factors-tacrolimus ,MMF and steroid were given from 2-7 days prior to transplantation, keeping trough level of tacrolimus from 12-15 ng/ml. CLINICAL OUTCOMES AFTER RENAL TRANSPLANTATION INVOLVING ABOI
Overall, transplants involving ABOi compared to those involving ABOc had a significantly higher mortality rates at 1, 3 and 5 years. The higher mortality rate is probably a consequence of the high immunosuppression related to the therapy. Indeed, some studies in which selected patients received a lower, tailored desensitization therapy reported an improved survival rate, with fewer infections and without ABMR. Accommodation:
It is lack of rejection in presence of circulating ABO antibodies with normal kidney function and normal histology and is facilitated by reduction of isoagglutinin levels, blocking of complement activation and rituximab. No role of protocol biopsies as far as ABO incompatible transplants are concerned. Complications:
Hemorrhage is more common in ABOi transplants, significantly associated with number of IA sessions.
Infectious complications have different incidence in different studies mostly vary according to intensity of desensitization.
AMR, the main cause of graft loss, related to level of isoagglutinin level at transplantation and presence of anti-HLA antibodies KPD :
Simplest model of the KPD -two-way, in which two pairs of donors and recipients with ABOi exchange the kidneys, thereby resolving the incompatibility.
A variant of domino KPD is the Never Ending Altruistic chain, which allows a higher number of recipients to be transplanted by the use of bridge donors . Making a choice between desensitization and KPD
KPD is cheaper but may be associated with prolonged waiting time.
Costs of KPD is similar to ABOc kidney transplants
According to data from US, overall KPD is increasing while desensitization strategies are decreasing.
Ahmed Omran
3 years ago
Blood group antigens are present in RBCS and in the endothelial cells including A, B, AB, O
Patient having blood group A have antibodies against B antigen ,and those with blood group B has anti -A antibodies
Individuals with blood group O have no antibodies so considered universal donors, and patients with blood group AB are universal recipient.
Blood group A is subdivided into A1 and A2. A2 antigen accounts for 20 % of white race individuals with blood group A, and is less expressed on RBCS than A1 ; recipients with anti-A sera ( those with blood group B, O) can receive kidneys from donors with blood group A2 if anti-A sera is low; ie individuals with blood group A2 can serve as universal donors with low titer of antibodies. Desensitization protocols – B cell depletion
* splenectomy is replaced by rituximab due to its side effects including infection with encapsulated organisms & surgical complications
*Rituximab produce splenic B cell depletion decreasing risk of rebound, but it spares plasma cells since they contain no CD20 receptors, so its benefit is uncertain
*Aiming to reduce cost, trials were done to reduce use of Rituximab or remove it from desensitization protocols or give it only on demand ; if titer > 1/16 with a good outcome:
– 35% of desensitization protocols are using Rituximab
– Antibodies depletion
Antibody depletion usually is assessed 2 weeks before transplantation , the indication and the frequency depend on isoagglutinin titer at that time, 1 session of PE can decrease the titer by one dilution hence number of sessions can roughly be estimated.
The aim is to achieve isoagglutinin titer of ≤1:8, patients with initial low titer have doubtful benefit of plasma exchange .
*PP (remove 20 % of antibodies per session), less effective, remove also coagulation factors resulting in bleeding tendency
*Double filter plasmapheresis, with fewer complications as a second filter is used which allows for the return of small molecules
* IA which is a specific technique that selectively removes IgG with the least side effects (produce 2-4 fold titer reduction per session), but more expensive ( 2-3 times more than plasmapheresis)
Antibody depletion usually is assessed 2 weeks before transplantation , the indication and the frequency depend on isoagglutinin titer at that time, 1 session of PE can decrease the titer by one dilution so the number of sessions required can roughly be known
The goal is to achieve isoagglutinin titer of ≤1:8, in patients with initial low titer benefit of plasma exchange is debatable
– IVIG
IVIG is usually given following PP, but one regimen suggested to give 0.5 gm/kg in 1 dose the day before transplantation or in 2 doses 4 and 1 day before transplantation
It acts as an immunomodulator by blocking Fc receptors , so it prevents the rebound increase in antibody by plasma cells, and helping in replacement of immunoglobulins removed during PE or IA
Immunosuppression
Induction using either basiliximab or ATG
Maintenance using CNI better tacrolimus, MMF, and steroids ;steroid withdrawal is not recommended)started 2-7 days before transplantation.
Monitoring
As there is a high possibility of a rebound increase in antibodies post-transplantation with a risk of ABMR more in the first week
Three techniques are used : tube, gel and flowcytometry
The most sensitive is Flowcytometry but the problem is the cost and availability, followed by gel then tube technique
Monitoring of isoagglutinin titers is done on daily basis till discharge form the hospital, then 2-3 times weekly for the first month then weekly till 3 m post-transplant then yearly
If posttransplant isoagglutinin titer increases, the patient should be considered for renal biopsy (especially in case of renal dysfunction) and for preemptive PP
Outcome
ABO-incompatible transplantation is associated with lower patient survival at 1, 3, and 5 years post-transplantation but patient survival at 8 years is similar to ABO compatible transplantation. This may be explained by increase in the risk of infections and sepsis including pneumonia, UTI, wound infection, PCP, CMV and BK virus, in addition to coagulopathy induced by PP
There is a significant increase in the risk of ABMR but not acute CMR in patients with ABOi transplantation and graft survival reduction. C4d can be present in biopsy with no features of ABMR due to accommodation, so significance of C4d staining is less in ABO I transplantation
Complications include bleeding ( the most common surgical complications related to ABO I transplantation ), increase in risk of infections and sepsis in ABOi compared to compatible transplantation and significant increase in the risk of ABMR in patients with ABOi transplantation
ABO I transplantation is considered expensive.
Theepa Mariamutu
3 years ago
Transplantation of living donor is an option to avoid long term dialysis complications but obstacles are faced including immunological barrier, which could be HLA and or ABO incompatibility , in order to solve this problem 2 strategies are applied which are desensitization and paired kidney exchange program.
The most frequent protocols: Removal of circulating ABO antibodies
Using plasmapheresis or immune-adsorption (IA) and apharetic technique which is the most updated technique in order to lower the circulating anti-A/B antibody levels to reach titers between 1:8 and 1:32.
plasma pheresis eliminates 20% of Ab in a session along with coagulation factors and protective Ab.
double filtration plasmapheresis allows return of essential components to the blood there by avoiding PP drawbacks.
IA selectively eliminates humoral factors using immobilised Ab or immobilised staph protein A or immobilized antigens and synthetic epitopes
Immunomodulation
Using IVIG having immunomodulatory role and replacing Ig lost in apheresis
B cell depletion
Using splenectomy which is currently replaced by Rituximab
Accommodation can occur protecting the kidney on the long term because by lowering ABO Ab titer graft can gain within 2 weeks a capacity to resist complement damage.
Genberg et al study mentioned that ABO incompitable transplant cases treated 30 days before transplantation with IA and Rituximab and IVIG one day before transplantation showed no significant difference between ABO compatible and incompatible groups regarding patient , graft survival and rejection.
Another study stated that stopping IA can cause rebound increase in Ab titer
The generally applied strategy is using Rituximab 10 days before Transplantation(Tx) and plasma pheresis /IA 1week before and after Tx along with 2 doses of IVIG prior Tx
Other policies used to lower Rituximab dose or decrease IA frequency with acceptable outcomes, concluding that individualising desensitisation has favourable net results.
Clinical outcomes after Renal Tx of ABOi cases
ABOi Tx showed comparable outcomes to ABO c Tx but this was concluded from studies done on small number of cases
2 studies were done with bigger number of patients mentioned that Rituximab and IA have great efficacy but these studies had limitations.
More studies are needed to detect best protocols for cases with low pretransplant anti-ABO antibody titers
According to Anti A /B Ab titer desensitization protocols are
If Ab titer <8—–induction and maintenance therapy
If 8 —-Rituximab— induction and maintenance therapy
If16-64—-Rituximab +DFPP—- induction and maintenance therapy
If>264—-Rituximab+IA—- induction and maintenance therapy
Mortality rate is higher in ABOi Tx than ABO c Tx at 1,3 ,5 years could be due to extensive immunosuppression , coagulation disorders and infectious complications ,while graft loss and mortality is equal in both groups at 8 years post transplantation
Controversies in ABO i Tx Technique of apheresis
The high cost of specific columns used because it is efficient than other columns lead to reusage of those specific columns
It seemed that aphaeresis could be benefice even in cases with low Ab titers to decrease inflammatory molecules level
RTX role
It replaced splenectomy , it lowers the risk of isoagglutin rebound , the risk of ABMR and the risk of chronic rejection.
IVIG
It blocks FC receptor on leucocytes, inhibit complement activation and HLA Ab, also it decreases Ab rebound after Tx ,decreasing ABMR risk
Isoagglutinin quantification
Detected by flux cytometry , tube and gel technique .
On the other hand it has no predictive value for ABMR.
Immunosuppression
For ABOi cases is the same as for standard transplantation. It starts with the desensitization.
Post-transplantation apheresis
Is done for patients with abnormalities of graft function and with isoagglutinin rebound
Accommodation
Is the presence of circulating isoagglutinin and antigens on the graft cells with tolerance and less rejection risk due to due to the presence of a low titer of antibodies, with low affinity and with the blockage of complement activation.
Eculizumab can enhance accommodation.
Protocol biopsy role
C4d presence in grafts of ABOi Tx can be related to accommodation in the absence of clinical or other histological abnormalities
Complications
Surgical complications is the same for ABO incompatible and compatible Tx except hemorrhage is more common in ABO ic group due to aphaeresis , number of IA done
Infection complication is dependent on desensitsation policy
ABMR risk varies according to the isoagglutinin level at transplantation and the presence of anti HLA
Kidney paired donation (KPD)
It includes 2 ,3 ,4 way and so on
Domino KPD allows a higher number of recipients to be transplanted by the use of bridge donors
Some issues are highlighted :
transport of door versus the organ
Simultaneous versus non simultaneous exchange
Closed chains vs open chains
National Kidney Registry in the United States, revealed that KPD is increasing , while the desensitization strategy is decreasing
CARLOS TADEU LEONIDIO
3 years ago
Summarise this article
INTRODUCTION
Approximately 30% of such transplantations are considered incompatible from the immunological point of view either because of the presence in the recipient of antibodies directed against the human leukocyte antigen (HLA) antigens of the donor or because of the incompatibility of the ABO system between the donor and recipient or because of both. There are two principal strategies to overcome these barriers: (1) To desensitize the recipient to remove the antibodies and modify the immunological status, allowing the transplant; and (2) To exchange the organs between two or more pairs to exchange the organs between different donors. The aim of this review is to give a general overview of ABO incompatibility (ABOi), the techniques used to overcome ABOi, the removal of the immunological barriers, and the outcomes obtained. In the last part of the review, kidney paired donation (KPD) will also be briefly discussed.
IMUNOLOGICAL ASPECTS
The reaction of isoagglutinins with the antigens of the ABO group induces complement activation, as documented by the presence of C4d. In addition to its relation with the development of ABMR, the presence of C4d on the tissues may also be associated with the development of chronic rejection.
TECHNIQUES OF ABO DESENSITIZATION AND DIFFERENT PROTOCOLS USED OVER TIME
Removal of circulating ABO antibodies
The removal of circulating ABO antibodies is obtained principally by plasmapheresis or immune-adsorption (IA). The aim of these strategies, principally applied several days before transplantation, is to reduce the circulating anti-A/B antibody levels to achieve titers between 1:8 and 1:32.
Among the techniques used to induce desensitization, the apheretic techniques are those with the most relevant evolution since the beginning. The simpler, cheaper, but less effective technique has been the therapeutic plasma exchange using highly permeable membranes. The procedure eliminates approximately 20% of the antibodies by session. Additionally, removes protective antibodies and coagulation factors. The double filtration plasmapheresis is performed by two plasma filters, and the second one allows smaller molecules to return back to the patient, avoiding many complications associated with the therapeutic plasma exchange.
A further evolution has been made by the use of columns for the selective removal of humoral factors by IA. A Therasorb column contains polyclonal sheep anti-human IgG antibodies and is effective in removing IgG antibodies. A different IA technique uses immobilized staphylococcal protein A. These Immunosorba columns, that contains staphylococcal protein A bound to sepharose is effective in removing IgG of different classes. Additionally, are able to induce a B cell apoptosis, so enhancing the immunosuppressive effect. Another IA technique uses immobilized antigens and synthetic epitopes and is the most specific technique in removing only the undesirable antibodies
Immunomodulation
This technique consists in the administration of high doses of polyclonal intravenous immunoglobulin (IVIG) to the patient before transplantation, blocking the Fc receptor and has immunoregulatory properties.
B cell depletion
B cells produce isoagglutinins, and their reduction is essential to obtain effective desensitization. Historically, splenectomy has been used principally in Japan for B cell depletion. To date, RTX, a humanized monoclonal antibody that binds to CD20 expressed on the B cell membrane, is the drug used to obtain B cell depletion.
When exposed to a low ABO antibody titer, the transplanted kidney develops in approximately 2 wk the capacity to resist complement-mediated damage. The phenomenon of lack of rejection in the presence of circulating ABO antibodies complement activating is known as accommodation. Accommodation is also responsible for kidney protection over a long period of time.
In the literature different protocols exist that have been changed over time, so advantages and disadvantagesneed to be discussed.
CLINICAL OUTCOMES AFTER RENAL TRANSPLANTATION INVOLVING ABOI
The results obtained after renal transplantation involving ABOi and reported in this review are generally good and overlap with the results obtained in ABOc renal transplantation. However, the results reported generally refer to studies with a low number of patients.
Overall, the evidence of the benefits of the different preconditioning therapies is low, although it seems that patients receiving the newest therapies have a better outcome with fewer severe side effects.
Overall, transplants involving ABOi compared to those involving ABOc had a significantly higher mortality rates at 1, 3 and 5 years ( P < 0.0001). Both graft losses and mortality in transplants involving ABOi became equivalent to ABOc transplants at 8 years after transplantation.
The higher mortality rate is probably a consequence of the high immunosuppression related to the therapy. Excess immunosuppression is the cause of severe bacterial or viral infections.
Coagulation disorders were also frequent in transplant involving ABOi. This complication is probably related to the modifications in the coagulation system induced by plasmapheresis or IA. The use of a high dose of RTX or the use of other immunosuppressants to reach a higher desensitization was also associated with a higher mortality rate due to infectious disease.
Polyoma virus nephropathy was also more frequent in patients receiving RTX, as documented by several authors. All of these findings on the higher mortality rate in transplants involving ABOi, probably related to the side effects of high immunosuppression are in favor of tailored immunosuppression. Indeed, some studies in which selected patients received a lower, tailored desensitization therapy reported an improved survival rate, with fewer infections and without ABMR.
OPEN CONTROVERSIES IN KIDNEY TRANSPLANTATION INVOLVING ABOI
The different and discordant results reported by the different authors highlight the controversies that are still open in kidney transplantation involving ABOi. The vast majority of controversies concern the strategies of desensitization.
Technique of apheresis
The costs of IA are 2-3 times higher than those of plasmapheresis. Some studies have suggested the reuse of columns to reduce the costs.
The number of apheresis treatments differs according to the basal levels of isoagglutinins and the center. Almost all centers try to reach a titer of 1:8 before transplantation. A relevant question is what to do with patients with a low titer of isoagglutinins. Several centers have reported good results in these patients with few or no apheresis treatments.
Role of RTX
The use of RTX has allowed the avoidance of splenectomy since 2002. The use of RTX in kidney transplantation involving ABOi does not seem to be necessary in all patients. In the meta-analysis already mentioned, only 35% of patients were treated with RTX. The use of RTX reduces the risk of isoagglutin rebound and the risk of ABMR. In addition, the risk of chronic rejection seems to be reduced by the use of RTX.
IVIG
Among the various effects of IVIG on the immune reaction, the most common are: (1) Blockage of the Fc receptor on the leukocyte membrane; (2) Inhibition of the complement activation; and (3) Inhibition of circulating antibodies against HLA. In transplants involving ABOi, the IVIG administration reduces the antibody rebound after transplantation and the risk of ABMR.
Isoagglutinin quantification
To decide on the immunosuppression and in particular the apheresis technique to be used, it is necessary to know the isoagglutinin titer. The best method is flux cytometry , even if the method has a high cost. The tube and gel techniques for ABO antibody titration are also frequently used. However it should be highlighted that both the antibody basal titer before desensitization and the post-transplantation titer have a low predictive value for ABMR.
Immunossupression
The possibility of steroid withdrawal is discussed. Some studies have documented a high risk of ABMR in the case of steroid withdrawal soon after transplantation. Other studies have documented a high risk for acute rejection even in the case of late withdrawal . Overall, patients receiving transplant involving ABOi are not allowed to reduce immunosuppression.
Post-transplantation apheresis
Apheresis treatments post-transplantation are reserved for patients who present abnormalities of graft function together with isoagglutinin rebound. It does not attain beneficial effects in patients without graft dysfunction.
Accommodation
Accommodation in renal transplantation involving ABOi has been defined as the presence of circulating isoagglutinins and antigens on the graft cells with normal renal function and normal histology. By 2006, the American Society of Transplantation established a consensus on the accommodation status and added the presence of C4d on the peritubular capillaries . The pathogenesis of the accommodation seems to be due to the presence of a low titer of antibodies, with low affinity and with the blockage of complement activation. Under these conditions, endothelial cells develop a phenotypic change according to which they become resistant to antibody damage.
Eculizumab, a monoclonal antibody against C5, may facilitate accommodation. In addition, eculizumab may allow a safe transplantation in patients with ABOi with high antibody titers and may represent a rescue therapy in the case of severe ABMR.
Role of protocol biopsies
In summary, the presence and the role on protocol biopsies of C4d in transplantations involving ABOi seems to be related to accommodation when found in the absence of clinical or other histological abnormalities.
Complications
Surgical complications in transplantations involving ABOi are similar to complications of standard transplants, with the exception of hemorrhages. Hemorrhages are likely to be ascribed to the apheresis treatments.
The hemorrhages were significantly associated with the number of IA sessions.
The incidence of infectious complications is different across the studies. The difference is probably related to the intensity of desensitization strategies (the number and type of apheresis treatments and the dose of RTX, IVIG and other immunosuppressants).
ABMR is the first cause of graft loss in transplantations involving ABOi. The risk for ABMR is related to the isoagglutinin level at transplantation and to the presence of anti-HLA antibodies.
KIDNEY PAIRED DONATION ( KPD)
The hypothesis of overcoming the immunological barriers in a different way without the desensitization. The simplest model of the KPD is the two-way, in which two pairs of donors and recipients with ABOi exchange the kidneys, thereby resolving the incompatibility . The model may also include a higher numbers of pairs realizing the KPD at three-way, four-way, and so on. Several programs exist worldwide and with the increasing number of KPD programs, it has been possible to achieve a global kidney Exchange.
KPD programs have several points that yet need to be better clarified. The principals are as follows:
-Transportation of kidneys vs donor travel: This happens when two or more transplant centers are involved. The travel of the donor has a cost, and the donor will be operated on by an unknown surgical team. The travel of the organ minimizes the costs and allows the continuity of donor care.
-Simultaneous vs no simultaneous exchanges: Simultaneous donation has the advantage that no donor will change his mind. The drawback of simultaneous donations is logistical, principally if multiple organ donors will be operated on in the same center.
-Closed chains vs open chains: The channels of transplantations initiated by a non- donor may be extended but should end with donation to a recipient on the waiting list .
MAKING A CHOICE BETWEEN DESENSITIZATION AND KPD
KPD is generally cheaper with respect to desensitization, it remains to be answered the availability of KPD in a short time. This fact depends by the hospital or the national organization. The kidney exchange may base on a single center strategy, on a regional strategy on a national or international strategy.
CONCLUSION
The immunological barriers represented by the different ABO groups have been overcome. The two mechanisms responsible for this success are the accommodation and the achievement of some humoral tolerance. The most important techniques are those of desensitization and of isoagglutinins removal. In this field a relevant role have the immunoadsorption and the use of anti CD20 antibodies that allowed avoiding the splenectomy.
Finally, it should be also considered that though the ABOi transplants are more expensive than the ABOc transplants, however they are less expensive than dialysis.
Huda Al-Taee
3 years ago
Summarise this article
Renal transplantation is considered the best therapy for ESRD patients. There are many problems that hinder this process such as cadaveric renal donor shortage, advanced age, immunological reactivity, or issues related to surgery or cardiovascular disease.
approximately 30% of such transplantations are considered incompatible either because of HLA or ABO incompatibility.
There are two principal strategies to overcome these barriers:
To desensitize the recipient to remove the antibodies and modify the immunological status, allowing the transplant.
To exchange the organs between two or more pairs to exchange the organs between different donors.
Development of the practice of ABOi Tx:
ABOi has been considered an absolute contraindication to kidney transplantation. For the first time.
Brynger et al reported the clinical outcomes of 21 renal transplantations from A2 donors to O recipients.
Principally after 1998, there was a worldwide increase in the rate of kidney transplantations from living donors that involved ABOi, this is due to the improvement of knowledge of the diagnosis and treatment of ABMR, results of a Japanese study of ABOi Tx, Johns Hopkins University and the Mayo Clinic documented the possibility of performing such transplantation without splenectomy with the administration of rituximab, Swedish authors developed a new technique that demonstrated outcomes in renal transplantation involving ABOi that were similar to the outcomes of standard renal transplantation.
Techniques of ABO desensitization and different protocols used over time:
Removal of circulating ABO antibodies:
Obtained through either PP or IA.
The aim is to reduce the circulating anti-A/B antibody levels to titers between 1:8- 1:32.
Immunomodulation:
Consists of the administration of high doses of IVIG.
The aim is to replace the patient’s Ig that is lost because of the apheresis technique.
B cell depletion:
Previously, this was done by splenectomy, nowadays it is replaced by rituximab.
Clinical outcomes of ABOi Tx:
The results of ABOi Tx are generally good and overlap with the results obtained from ABOc Tx.
Most of the studies in this field are small with the exception of Barrett’s study.
Two systematic reviews and meta-analyses were done in this field but their limitation was the absence of RCTs, they only highlight the possibility that rituximab & IA could have superior efficacy.
A more recent systematic review showed that in ABOi Tx higher mortality rates at 1,3, and 5 years but mortality and graft loss become equivalent to ABOc Tx at 8 years. both coagulation disorders and BK virus nephropathy were higher in ABOi Tx.
Open controversies in ABOi Tx:
The different and discordant results reported by the different authors highlight the controversies that are still open in kidney transplantation involving ABOi. The vast majority of controversies concern the strategies of desensitization.
Technique of apheresis:
Whether to use specific or non-specific column IA, the no. of apheresis treatment, and what to do with a low titer of isoagglutinin.
Role of rituximab:
The use of rituximab helps to avoid splenectomy, however, not all patients require its use, but it reduces antibody rebound and the risk of ABMR, and also it reduces the risk of chronic ABMR.
IVIG:
It reduces antibody rebound after transplantation, and different protocols are used for its dose.
Isoagglutinin quantification:
Both the antibody basal titer before desensitization and the post-transplantation titer has a low predictive value for ABMR.
Immunosuppression:
Regarding steroid withdrawal, Some studies have documented a high risk of ABMR in the case of steroid withdrawal soon after transplantation. Others showed a high risk for acute rejection even in the case of a late withdrawal.
Post-transplant apheresis:
According to several authors, the treatment by apheresis post-transplantation does not attain beneficial effects in patients without graft dysfunction, while others perform post-transplantation apheresis in patients with isoagglutinin rebound or with high basal levels of antibodies.
Accommodation:
Is the presence of circulating isoagglutinin and antigens on the graft cells with normal renal function and normal histology.
The pathogenesis of the accommodation seems to be due to the presence of a low titer of antibodies, with low affinity and with the blockage of complement activation, so endothelial cells become resistant to antibody damage.
This process is facilitated by the reduction of the isoagglutinin level, RTX, IA- specific columns, and Eculizumab.
Role of protocol biopsies:
Studies showed that there is no difference in the histological pattern for patients with protocol biopsies done at 3 & 12 months post-transplant.
Complications:
Surgical complications are similar to complications of standard transplants, with the exception of haemorrhages.
The incidence of infectious complications is different across the studies.
ABMR is the first cause of graft loss & occurs usually in the first 2 wk post-transplant.
KPD:
The simplest model of the KPD is two-way, in which two pairs of donors and recipients with ABOi exchange the kidneys, and there are other forms such as 3 or 4 ways.
Several programs exist worldwide, and it has been possible to achieve a global kidney exchange.
Further increase in kidney exchanges was realized by the domino KPD, which starts from an altruistic donor and finishes with the donation of a kidney to a recipient on the waiting list.
KPD programs have several points that yet need to be better clarified:
Transportation of kidneys vs donor travel.
Simultaneous vs no simultaneous exchanges.
Closed chains vs open chains.
Making choice between desensitization and KPD depends on the hospital or the national organization.
Weam Elnazer
3 years ago
Each of the four ABO blood types belongs to one of the four categories (A, B, AB and O). Antigens that are not native to the host are responsible for the development of anti-blood group antibodies. Individuals belonging to Group O exhibit greater antibody titers against both the A and B antigens.
Patients in Group O have greater anti-A/B antibody titers, which leads to a higher incidence of AMR after transplantation, while kidneys from A2 donors to O recipients had better outcomes.
-It was discovered that ABOi was a contraindication to kidney transplantation, which led to the development of kidney transplantation practices in ABOi couples.
However, the number of ABOi transplants has grown globally as a result of AMR diagnosis and therapy is becoming more accurate.
It was shown that the results of ABOi transplants were comparable to those of standard-risk transplants.
-Techniques for ABO desensitization, as well as other procedures, are employed:
Remove circulating ABO antibodies: Plasmapheresis (PP) is a more affordable and straightforward method of removing circulating ABO antibodies; but, it is less successful; it removes only 20 per cent of antibodies each session, as well as protective antibodies and coagulation factors.
Double filtration PP is safer than single filtration PP because it allows for the return of smaller molecules to the patient. Immunomodulation: A high dosage of IVIG is used to replenish immunoglobulins that have been lost via the use of apheresis procedures, as well as for its immunoregulatory effects, which are intended to reduce antibody rebound and the risk of AMR.
B cell depletion: Splenectomy has been substituted with rituximab in order to achieve B cell depletion and reduce agglutinin titer to a preset level.
The protocols that are being employed are a combination of such tactics, with many efforts being made to lessen the difficulties and costs connected with them.
Clinical consequences include:
Transplant studies with ABOi patients are often conducted with small numbers of participants.
-Overall, transplants involving ABOi were associated with considerably higher death rates at 1, 3, and 5 years as compared to transplants involving ABOc. The increased death rate is most likely a result of the high level of immunosuppression associated with the treatment. Indeed, several trials in which chosen individuals got a lower dose of customized desensitization treatment showed an increased survival rate, with fewer infections and no evidence of atypical bacterial meningitis.
-Surgical complications in ABOi transplantations are comparable to those seen in normal transplants, ABMR is the most common cause of graft loss in ABOi transplantations, accounting for almost half of all graft losses.
-KPD, 2 pairs of donors and recipients with ABOi exchange kidneys; the number of pairings may be increased to encompass a greater number of donors and recipients.
-KPD is less expensive, however, it may be linked with a longer waiting period.
The costs of KPD are comparable to those of ABOc kidney transplants.
nawaf yehia
3 years ago
Although renal transplantation is considered the best therapy for patients affected by end-stage renal disease , however , approximately 30% of such transplantations are considered incompatible from the immunological point of view either because of the presence in the recipient of antibodies directed against the human leukocyte antigen (HLA) antigens of the donor or because of the incompatibility of the ABO system between the donor and recipient or because of both .
IMMUNOLOGICAL ASPECTS
The antigens of the ABO system are glycoproteins expressed on erythrocyte membranes as well as on epithelial and endothelial cells. At the renal level, these glycoproteins are also expressed on the collecting and distal tubules and on the vascular endothelial cells
The reaction of isoagglutinins with the antigens of the ABO group induces complement activation, as documented by the presence of C4d
having both types of Ab ( Anti A & Anti B ) , recipients of blood type O have a higher incidence of antibody-mediated rejection (ABMR) after transplantation
In a graft from a donor with blood group type A of the A2 subtype , the A2 Ag is less expressed on tissues and thence confers less immunogenic risk .4
DEVELOPMENT OF THE PRACTICE OF KIDNEY TRANSPLANTATION IN
ABO- INCOMPATIBLE PAIRS
For a long time, ABOi has been considered an absolute contraindication to kidney
transplantation but with the evolving desensitization protocols it has become increasinglyy adopted with good outcomes
TECHNIQUES OF ABO DESENSITIZATION AND DIFFERENT PROTOCOLS
USED OVER TIME
The most frequent protocols applied to obtain desensitization in pairs with ABOi are a
mixture of the following strategies.:
Removal of circulating ABO antibodies
The removal of circulating ABO antibodies is obtained principally by plasmapheresis
or immune-adsorption (IA). The aim of these strategies, principally applied several
days before transplantation, is to reduce the circulating anti-A/B antibody levels to
achieve titers between 1:8 and 1:32.
the apheretic techniques is the principle of desensitization and carried out by different ways :
1)The simpler, cheaper, but less effective technique has been the therapeutic plasma
exchange using highly permeable membranes. The procedure eliminates
approximately 20% of the antibodies by session. Additionally, removes protective
antibodies and coagulation factors.
2)The double filtration plasmapheresis is performed by two plasma filters, and the
second one allows smaller molecules to return back to the patient, avoiding many
complications associated with the therapeutic plasma exchange.
3)further evolution has been made by the use of columns for the selective removal
of humoral factors by Immunoadsorption IA .
Immunomodulation
This technique consists in the administration of high doses of polyclonal intravenous
immunoglobulin (IVIG) to the patient before transplantation. The aim is to replace the
patient’s immunoglobulins lost because of apheresis techniques. In addition, IVIG
blocks the Fc receptor and has immunoregulatory properties
B cell depletion
Being the producers of iosagglutinins , B cell depletion is essential to have effective desensitization . Historically it was achieved with splenectomy but the use of Anti CD 20 Rituximab has largely replaced splenectomy and is almost abandoned nowadays .
CLINICAL OUTCOMES AFTER RENAL TRANSPLANTATION INVOLVING
ABOI
The results obtained after renal transplantation involving ABOi and reported in this
review are generally good and overlap with the results obtained in ABOc renal
transplantation.
The main limitation of the review is the lack of randomized controlled trials. As a consequence, the systematic review does not allow us to compare the different therapies. The review only highlights the possibility that RTX and IA could have a superior efficacy, although this point remains to be confirmed by randomized controlled trial .
studies conducted on ABOi KT patients evaluated pateint and graft survival according to the preconditioning therapy
. Overall, transplants involving ABOi compared to those involving ABOc had a significantly higher mortality rates at 1, 3 and 5 years (odds ratio 2.17, 1.89 and 1.47, respectively; P < 0.0001). Both graft losses and mortality in transplants involving ABOi became equivalent to ABOc transplants at 8 years after transplantation.
The higher mortality rate is probably a consequence of the high immunosuppression related to the therapy which is leading cause for severe bacterial or viral infections , in this regard ,Polyoma virus nephropathy was also more frequent in patients receiving RTX
Coagulation disorders were also frequent in transplant involving ABOi. This complication is probably related to the modifications in the coagulation system induced by plasmapheresis or IA
OPEN CONTROVERSIES IN KIDNEY TRANSPLANTATION INVOLVING
ABOI
The different and discordant results reported by the different authors highlight the
controversies that are still open in kidney transplantation involving ABOi. The vast
majority of controversies concern the strategies of desensitization , The most common controversies are the following :
1.Apheresis technique used
Although specific IA is superior to others but still it is costy and not widely available
2.Role of rituximab
The use of RTX reduces the risk of isoagglutin rebound and the risk of ABMR. In
addition, the risk of chronic rejection seems to be reduced by the use of RTX
3.Utility and role of IVIG
In transplants involving ABOi, the IVIG administration reduces the antibody
rebound after transplantation and the risk of ABMR
4.Method to detect isoagglutinins quantity
To decide on the immunosuppression and in particular the apheresis technique to be
used, it is necessary to know the isoagglutinin titer.
The best method is flux cytometry, even if the method has a high cost. The tube
and gel techniques are also frequently used
5.Type of immunosuppression
Apart from desensitization, the immunosuppression in kidney transplantation with
ABOi is similar to that used for standard transplantation. The basal immunosuppression begins together with the desensitization.
6.Utility of posttransplantation apheresis
Apheresis treatments post-transplantation are reserved for patients who present
abnormalities of graft function together with isoagglutinin rebound
7.Accommodation
Accommodation in renal transplantation involving ABOi has been defined as the
presence of circulating isoagglutinins and antigens on the graft cells with normal renal
function and normal histology , this is usually gained with good desensitization and Ab depletion
8.Role of protocol biopsies
Here it is worthy to know that the presence and the role on protocol biopsies of C4d in
transplantations involving ABOi seems to be related to accommodation when found in
the absence of clinical or other histological abnormalities.
9.Principal complications
#surgical hemorrhage is more due to the coagulation factors loss in aphresis therapy that is also proportional to the No. of sessions
#intensified immunosuppression and the resulting infections
# ABMR is the first cause of graft loss in transplantations involving ABOi. The risk
for ABMR is related to the isoagglutinin level at transplantation and to the presence of Anti HLA Abs
KPD
It is an option to overcome the immunologic barriers without desessitization .
its simplest model is the two-way , With the increasing number of KPD programs, it has been possible to achieve a
global kidney exchange. Starting from a single-center experience, a state wise
experience was realized followed by a national program and an international
program .
MAKING A CHOICE BETWEEN DESENSITIZATION AND KPD
An answer to this question is difficult to be given. Indeed, given the fact that KPD is
generally cheaper with respect to desensitization, it remains to be answered the
availability of KPD in a short time.
saja Mohammed
3 years ago
Introduction: Both the ABO I and HLA I kidney transplant account for 30% of the living donor kidney transplant, By history the ABOI KT was considered absolute contraindication for kidney transplantation due to hyper acute rejection and graft loss . The main two approaches to overcome this problem are by using different desensitization protocol to target antibodies removal pre-transplant and prevent the ABS rebound after transplantation or by using the kidney exchange program. This review article focuses on reviewing the most recent evidence from the literature of the different desensitization protocols and ABO I kt clinical outcome. Also highlight the improvement of the different techniques of desensitization overtime including the use of more selective and specific type of apheresis for selective ABS removal with less side effects like moving from plasmapheresis to immunoadsorption (IA)Techniques with lower risk of infection and coagulopathy also moving from surgical B cell depletion by splenectomy which have been replaced nowadays by rituximab anticd20 monoclonal agent additionally with the improvement in our Knowledge about the immune system and the use of molecular assays for monitoring this help to adopt the strategies to personalized the immunosuppression protocols to avoid intense immunosuppression and reduce the risk of infection, malignancy, overall kidney transplantation from ABOI living donors nowadays consider a safe and effective approach that help in increase the donor pool and reduce the waiting list with overall similar outcome compared to ABOc kidney transplantation.
DEVELOPMENT OF THE PRACTICE OF KIDNEY TRANSPLANTATION INABO- INCOMPATIBLE PAIRS
The use of ABOI kidney transplant increased in numbers worldwide with good outcome , A2 donor blood group to O recipient Kidney transplant shows very promising results Different techniques have been used as part of desensitization protocol and by principle no consensus about the best protocol and should be individuated case by case Usually using combination therapies
Therapeutic plasmapheresis in the range of 3-5 sessions targeting the antibodies removal by 20% , its cheap, available and less cost while the introduction of IA techniques is preferable more selective and specific for removal of anti A/B antibodies from the circulation with target titer < 1-16 or, 1.36 and associated with lower risk of complement activation less coagulopathy or infection but rather more cost. IVIG act as immunomodulating agent, replace the Ig lost during plasmapheresis, block the FC receptors in activate T and B cells and enhance B cells apoptosis, different dosing, low or high dose after each session of plasmapheresis and additional dose at day of induction of 0.5gm/kg . B Cell depletion was very important part of any desensitization protocol, as the B Cell responsible for production of isoagglutinin’s .Historically surgical B Cell deleting by splenectomy which was used as part of desensitization from old Japanese protocol and now replaced by rituximab anti -CD20 humanized monoclonal Abs single dose usually given 3- 4 weeks prior to transplantation date with very good results from many observational studies.
Trials address the further modification of desensitization protocol by adopting on demand strategies based on the isoagglutinin titer level and they individualized the desensitization protocol to avoid intense immunosuppression with its associated morbid complications, this on demand protocol target the use of less IA sessions and low dose rituximab of 200mg/m2 or rituximab alone based on the isoagglutinin titer with favorable outcome with less side effects and cost and comparable outcome to ABOc KTX with 1, 3 year follow-up . Isoagglutinin titer quantification by using different techniques with no standardized values and it consider of low predictive value for ABMR. However, the best assay by using flux cytometry. Plasmapheresis indication after transplantation only when there is clinical evidence of graft dysfunction with increasing antibodies titer post transplantation Accommodation:
referred to the state of stable graft function with no evidence of graft injury in the presence of low isoagglutinin titer with affinity and positive C4D staining in PTCS by protocol biopsies. Complication of desensitization:
1- post-surgical bleeding which is more related with the numbers of the plasma therapy or IAs sessions.
2-Infections including bacterial and viral infection
3- ABMR, in the range of 10-30%, depend on the baseline isoagglutinin titer and the presence of anti HLA Abs.
Kidney pair exchange program :
The national or international KPD program have been increased since many years with expanding the chains from close chain to open loop with NDD or bridge donor in domino chain that help the access for better matched LD with less cost and shorting waiting list. but its application associated with many logistics including the availability of KPD in short time , donor travel and cost , closed vs opened chain
however currently access to KPD increasing compared to desensitization
Last edited 3 years ago by saja Mohammed
Mohamed Fouad
3 years ago
Current protocols and outcomes of ABO-incompatible kidney transplantation
One of the most challenges in living renal transplantation is that a significant percentage are immunologically incompatible either because of the presence HLA antibodies directed against the HLA system of the donor or because of the incompatibility of the ABO system.
There are Two different strategies to overcome these barriers: first is desensitization of the recipient to remove the antibodies either against HLA antigens or iABO antibodies and to prevent their rebound after transplantation and the second option is exchange of organs between two or more pairs what is called paired kidney exchange.
The number of renal transplantations between ABO-incompatible pairs have been increased because of improved knowledge of the immune system and the availability of new drugs. Rituximab has substantially replaced splenectomy. Also, the technique of plasmapheresis eliminates the preformed alloantibodies, and high-dose intravenous immunoglobulins improve the immunomodulation. Recent reports document that the outcomes for iABO transplantation similar to the outcomes of standard transplantation.
The ABO antigens are glycoproteins expressed on erythrocyte membranes as well as on epithelial and endothelial cells. In the kidney, these glycoproteins are expressed on the collecting and distal tubules and on the vascular endothelial cells. The reaction of isoagglutinins with the antigens of the ABO group induces ABMR through complement activation, as documented by the presence of C4d as well as causing chronic ABMR.
TECHNIQUES OF ABO DESENSITIZATION AND DIFFERENT PROTOCOLS USED OVER TIME
1-Removal of circulating ABO antibodies which done by plasmapheresis or immune-adsorption,the aim of this procedure is to reduce the circulating anti-A/B antibody levels to achieve titers between 1:8 and 1:32. The double filtration plasmapheresis is performed by two plasma filters, and the second one allows smaller molecules to return back to the patient.
2-Immunomodulation :This includes administration of high doses of IVIG to the patient before transplantation. The aim is to replace the patient’s immunoglobulins lost with plasmapheresis . As well as IVIG blocks the Fc receptor and has immunoregulatory properties.
3-B cell depletion: Historically, splenectomy has been used principally in Japan for B cell depletion. Nowadays RTX, the anti CD20 expressed on the B cell membrane, is the drug used to for B cell depletion. The aim for B cell depletion is to reduce the isoagglutinin titer to accepted levels.
When the transplanted kidney exposed to a low ABO antibody titer, In 2 weeks it has the capacity to resist complement-mediated damage and develop form of accommodation.
CLINICAL OUTCOMES AFTER RENAL TRANSPLANTATION INVOLVING ABOI
The short and medium outcomes results obtained after ABOI renal transplantation reported in this review are generally good and overlap with the results obtained in ABOc renal transplantation. But the results reported obtained from studies with small number of patients.
Overall, transplants involving ABOi compared to those involving ABOc had a significantly higher mortality rates at 1, 3 and 5 years. Both graft losses and mortality in transplants involving ABOi became equivalent to ABOc transplants at 8 years after transplantation.
The higher mortality rate can be explained by infectious complications secondary to high immunosuppression therapy. Excess immunosuppression is the cause of severe bacterial or viral infections. Coagulation disorders were also a frequent complication is probably related to the modifications in the coagulation system induced by plasmapheresis or IA.
some studies in selected patients who received a lower, tailored desensitization therapy reported an improved survival rate, with fewer infections and without ABMR.
kumar avijeet
3 years ago
ABOi transplant previously considered a contraindication now is a possibility with 30%increase in tx rate due to dire need of organs.
ABO ag is an oligosaccharide Ag which is present on rbc,glomerulus,tubules, endothelium which reacts with anti-A and B titre that will cause early rejection.So the sole purpose of desensitization is reduction of ab titre to a safe limit of B>A2 in line of immunogenicity.
Here the main culprits are-
1.Antibody(IgG is imp than IgM,because IgM is intravascular hence amenable to removal)
2.B-cell/plasma cell
3.complement
Mode of removal/suppression-
1.ANTIBODY
A.plasmapheresis(nonspecific,albumin,coagulation proteins also removed along with20%reduction in Ab)
B.double filtration plasmapheresis(more specific,only albumin loss)
C.immuneadsorption(specific IA against anti-A or anti-B)(no loss of albumin)
2.B-CELL
A.splenectomy (not practised now)
B.Rituximab (low to high dose, replaced splenectomy with increase in death censored graft function and prevent rebound of ab titre during initial tx weeks)
3.COMPLEMENT-
A.eculizumab (very expensive)
B.IVIG-modulate the immunity by neutralization of antibody,complement,T-cell inhibition,supplement immunoglobulin deficiency, but increases antibody titre)
4.ATG/BASILIXIMAB induction with triple immunosuppression.
5.TAILORED DESENSITIZATION-
titre 8-only rtx
titre 16-64-plasmapheresis+rtx
titre >64-IA+RTX
OUTCOME-patient survival is less due to more infections,mdr bacteria colonization,bkvirus nephropathy, but malignancy risk is equal.
ABOi tx graft survival,patient survival ,death censored graft survival is equivalent to ABOc tx but initial survival is less due to increased infections and rejection.
MAIN CONTROVERSIES IN ABOi TX
A.Technique of apheresis-not standardized
B.Role of rtx-should be given 1mnth early as it’s action starts between 3wk to 6mnth, and should be in lower dose and avoided just before tpe.
C.ivig-dose not standardized, as commonly used 500mg/kg before tx.
D.isoagglutinin quantification-not standardized, but flowcytometry is best,with gel method preferred over tube method.
E.immunosuppression-steroid withdrawl should be avoided
F.post tx apheresis-should be performed post tx graft dysfunction with rebound of titre.
G.Accomodation-mainly due to low titre of antibody,complement deactivation, with phenotypic endothelial changes.
H.role of protocol biopsy-not so informative.
So concluding that desensitization should always be avoided in place of availability of kidney paired donation, but TIME ⏲️ plays the deciding role here.
mai shawky
3 years ago
· Blood group antigens are presented on RBCS , endothelial cells and renal tubular epithelial cells in certain circumstances, they include A, B, AB, O
· Patient with blood group A has anti B antibodies, while those with blood group B has anti -B antibodies.
· Individuals with blood group O has no antibodies so they are universal donors. However, patients with blood group AB are universal recipient.
· Blood group A has 2 subtypes: A1 (80 %) and A2 (20%, and less immunogenic).
Desensitization protocol
v B cell depletion
In the past surgically by splenectomy, now is replaced by rituximab to minimize surgical complications
Rituximab produce splenic B cell depletion thus decrease the risk of rebound, but it does not affect plasma as they lack CD20 receptors, thus its benefit till now is uncertain
Only 35% of desensitization protocols are using Rituximab
Rituximab takes 3-6 weeks in order to exert its full effect
v Antibodies removal
PEX (remove 20 % of antibodies per session), less effective, remove also coagulation factors leading to bleeding tendency and remove all IgG with higher risk of infection and sepsis.
Double filter plasmapheresis, has fewer complications than conventional plasmapheresis, as a second filter is used which allows for the return of small molecules
IA can selectively remove IgG with the least side effects (produce 2-4 fold titer reduction per session), but more expensive than plasmapheresis and not widely available.
Isoagglutinin titer is assessed 2 weeks before transplantation. The goal is to achieve isoagglutinin titer of ≤1:8.
v IVIG
IVIG is usually given after PEX, to reconstitute humoral immunity and prevent serious infections. In addition, it prevents the rebound increase in antibody by plasma cells.
v Immunosuppression;
Induction using either basiliximab or ATG according to other risk factors
Maintenance using CNI better tacrolimus, MMF, and steroids (steroid withdrawal is not recommended).
When started 2-7 days before transplantation, it decrease risk of AMR.
v Monitoring
Close monitoring of isoagglutinin titer is crucial since there is a high possibility of a rebound increase in antibodies post-transplantation with a risk of ABMR especially in the first week
Flowcytometry is the most sensitive method but expensive and not usually available, followed by gel then tube technique
Monitoring of isoagglutinin titers daily till discharge form the hospital, then 2-3 times per week for the first month then weekly till 3 m post-transplant then annually
If posttransplant isoagglutinin titer increases, the patient should be considered for renal biopsy (especially if there is renal dysfunction) and for preemptive plasmapheresis
Outcome
ABO-incompatible transplantation is associated with lower patient survival at 1, 3, and 5 years post-transplantation but long term patient survival at 8 years is comparable to ABO compatible transplantation, this may be attributed to the increase in the risk of infections and sepsis including pneumonia, UTI, wound infection, PCP, CMV and BK virus, also bleeding complications related to coagulopathy induced by PEX.
There is a significant increase in the risk of ABMR but not acute CMR with subsequent reduction in graft survival.
Diagnosis requires both the presence of histological features of ABMR and the presence of antibodies, C4d can be present in biopsy with no features of ABMR (accommodation) thus the significance of C4d standing is less in ABO I transplantation
Disadvantages of ABO i transplant:
Bleeding is the most common surgical complications related to ABO I transplantation due to removal of clotting factors by PEX.
Infections and sepsis in ABOi due to intense immunosuppressive therapy.
Higher risk of ABMR but not acute CMR
High Cost of desensitization and treatment of subsequent rejection episodes.
Sahar elkharraz
3 years ago
ABO incompatible are now possible for renal transplant and expensive due to desensitisation protocol, However is less costly in comparison to patients staying on dialysis.
This article focus on strategies of desensitisation protocol and choice between the PKD and desensitisation protocol.
ABOi results from glycoproteins expressed on surface of RBC and surface of many endothelial cells and epithelial cells especially collecting ducts and distal renal tubules. It’s responsible for hyperacute rejection and ABMR lead to activation of complement and graft loss. this high titer of anti A/B antibodies can removed by plasma exchange before and after transplant but double filtration plasma pharesis less complications because second filter lead to return small molecule to blood.
Selective immunoadsorption more benefit than non selective immunoadsorption in removal of IgG class and remove isoagglutinins.
Another step in desensitisation protocol is immunomodulation with high dose of intravenous immunoglobulin post plasma session to replenish immunoglobulin lost by plasma exchange.
B cell depletion by rituximab 375mg/m2 anti CD20 monoclonal antibody against B cell which replaced by Japanese in 2005 instead of splenectomy.
By this method graft survival smilar to ABOC but survival patients less due to infection because intensity of immunosuppressive drug.
Inhibition of complement activation by C5 inhibitors Eculizumab.
Maintenance therapy with triple immunosuppressive agents MMF and Calcinurine inhibitors and low dose steroid. there’s may history of rejection after withdrawal steroid in patients with ABOI.
There’s risk from surgical complications and coagulation disorder post plasma exchange and high risk of infection in those patients.
Serial graft biopsy at 3m and 12m to avoid ABMR. But most of them have accommodations phenomena presence of C4d deposition along peritubular capillarities and low titer of antibodies without evidence of graft rejection. Despite this improvement in ABOI transplant but declined in recent months due to development of PKD program from living donor compatible which are less expensive and less complications especially infection.
However there’s many issues of PKD program should be clarified regarding:
– [ ] kidney or donor travel
kidney travel less expensive than donor
– [ ] simulations and non simulation issues
– [ ] close chain versus open chain
Conclusion
PKD more safe than ABOI transplant because less expensive and less hazardous of infectious and non infectious complications.
Amit Sharma
3 years ago
· Summarise this article
ABO incompatibility hampers 30% of living donors from donating a kidney. ABO system antigens are glycoproteins on RBCs, vascular endothelial cells, collecting and distal tubules. AMR occurs due to membrane linked antigens as well as free circulating epitopes A and B. The isoagglutinins react with ABO group antigens, activating complement, giving a positive C4d stain.
There are 2 ways to overcome ABO incompatibility: either ABO incompatible transplants after desensitization, or a paired exchange transplant.
The techniques for ABO desensitization include:
1) Removal of circulating ABO antibodies: Either of the following methods can be used.
a.Therapeutic plasma exchange (TPE) using highly permeable membrane: A session decreases 20% antibodies, but also causes loss of protective antibodies and coagulation factors.
b. Double filtration plasmapheresis (DFPP): It prevents loss of smaller molecules, reducing the complication with TPE.
c. Immunoadsorption (IA) with immobilized antibodies: Most widely used, include columns containing polyclonal sheep anti-human IgG antibodies, or staphylococcal protein A.
2) Immunomodulation using IVIG: To replace the immunoglobulins lost and block Fc receptors as well as inhibit complement activation and circulating anti-HLA antibodies, reducing rebound and AMR.
3) B cell depletion: History splenectomy was done for B cell depletion, which has now been replaced by anti-CCD20 rituximab use which decreases tire rebound, chronic rejection and AMR rates.
The aim for desensitization is to reduce the isoagglutinin titres to a predetermined level prior to transplant, irrespective of the protocol used. The common features of all protocols include use of triple drug immunosuppression (in form of Tacrolimus, MMF and steroids), Plasmapheresis or immunoadsorption, IVIG with or without rituximab.
Various protocols used include:
1) Genberg et al: Rituximab 375 mg/m2 30 days before transplant, IA and IVIG 500mg/kg a day before transplant.
2) Japanese researchers: Rituximab replaced splenectomy after 2005.
3) Barnett et al: Tailored desensitization strategy according to isoagglutinin titres. <8: none, 8: rituximab, 16-64: rituximab with plasmapheresis, >64: rituximab with immunoadsorption.
To look for the outcomes of ABO incompatible transplants, 2 meta-analysis have been published.
Meta-analysis by Lo et al, although lacked randomized controlled trials, highlighted the possibility that rituximab with immunoadsorption might have a superior effect with fewer side effects with the evidence being of low level.
Another meta-analysis revealed higher mortality rates with ABO incompatible transplants at 1,3 and 5 years (consequent to increased infection due to higher immunosuppression, especially with rituximab use showing increased polyoma virus nephropathy) with equivalent graft and patient survival at 8 years. These findings emphasize the importance of a tailored approach for immunosuppression to decrease infections, mortality and AMR rates.
There are still some challenges in ABO incompatible transplants:
1) Controversy regarding method of apheresis: Different centres use different techniques with no consensus on best form of apheresis. IA have fewer side effects but higher costs.
2) Role of rituximab: Some centres do not use rituximab and have results similar to ABO compatible transplants.
3) Role and dose of IVIG: Some centres use 100 mg/kg after each plasmapheresis, some use 500 mg/kg one day prior to transplant, while others divide the dose in 2 sessions 4 day and 1 day prior to transplant.
4) Technique of isoagglutinin quantification: Flux cytometry is best but costly. Tube method and gel methods are more widely used. Although the basal titre pre-transplant and post-transplant titres have low predictive value for AMR.
5) Immunosuppression protocols: Steroid withdrawal shows poor results, hence not recommended.
6) Role of post-transplant apheresis: Only to be done if graft dysfunction with rising isoagglutinin titres, not on the basis of titre alone.
7) Role of protocol biopsies: It seems there is no role of protocol biopsies as far as ABO incompatible transplants are concerned.
8) Complications: Surgical complications, except for haemorrhages, are similar to ABO compatible transplants. Risk of AMR is high in first 2 weeks post-transplant, and is related to isoagglutinin titres at transplant and anti-HLA antibodies.
Kidney paired donation (KPD) is another way of transplanting ABO incompatible pairs but has certain unresolved issues like transporting kidneys versus transporting donors, simultaneous or non-simultaneous transplants and use of closed chains versus open chains. KPD is cheaper and more immunologically sound process and it should be encouraged as much as possible. ABO incompatible transplants can be offered after exhausting other avenues, but should be offered (with tailored approach) rather than keep waiting for a deceased donor.
Mohamed Saad
3 years ago
Current protocols and outcomes of ABO-incompatible kidney transplantation. INTRODUCTION:
Transplantation is the best modality of ESRD and pre-emptive LRKTX has the best outcome but there is an obstacle which is approximately 30% of such transplantations are considered incompatible from the immunological point of view due to (HLA or ABO incompatibility).
So to overcome this situation we can desensitize our patients with new protocol combined with Paired Kidney Donation. IMMUNOLOGICAL ASPECTS :
These oligosaccharides are expressed on the surface of a variety of different cell types, including RBCs, endothelial cells and kidney parenchymal cells.
Antigenic expression of A2 is quantitatively and qualitatively less than that of A1, immunogenic risk based on antigen expression alone is A1>B>A2.
The A2 subtype does not have circulating antigens linked to von Willebrand factor.
Better results in transplantation involving ABOi are obtained when transplanting kidneys from A2 donors to O recipients. TECHNIQUES OF ABO DESENSITIZATION AND DIFFERENT PROTOCOLS USED OVER TIME: A- Removal of circulating ABO antibodies.
PEX or IA to reduce the circulating anti-A/B antibody levels to achieve titers between 1:8 and 1:32.
PEX remove 20% of the antibodies by session, each option has its merits and demerits.
The double filtration plasmapheresis is performed by two plasma filters, and the second one allows smaller molecules to return back to the patient. B- Immunomodulation:
Intravenous immunoglobulin (IVIG) to the patient before transplantation aim is to replace the patient’s immunoglobulins lost because of apheresis techniques. C- B cell depletion:
Anti-CD 20 Rituximab now is considered medical splenectomy.
For B-cell depletion is used now by rituximab in most protocols.
Also some protocols not used rituximab at all if patient had reached an anti-A/B antibody titer of less than 1:32 with good graft survival.
The Guy’s Hospital, Barnett et al adopted their strategy according to the initial anti-ABO antibody titer . With a titer of 8, only RTX was used; with a titer between 16 and 64, plasmapheresis was added to RTX therapy; and with a titer > 64, IA and RTX were used. In total, 62 kidney transplants involving ABOi were performed using this strategy compared with 167 ABOc transplants. Showed that no difference was observed between the two groups in allograft and patient survival rates at 1 and 3 years or in the ABMR rates .
CLINICAL OUTCOMES AFTER RENAL TRANSPLANTATION INVOLVING ABOI
systematic review gives different results . This review examines 7098 renal transplantations involving ABOi shown that Overall, transplants involving ABOi compared to those involving ABOc had a significantly higher mortality rates at 1, 3 and 5 years which mainly due to higher mortality rate due to infectious disease or side effects of high immunosuppression.
Both graft losses and mortality in transplants involving ABOi became equivalent to ABOc transplants at 8 years after transplantation. OPEN CONTROVERSIES IN KIDNEY TRANSPLANTATION INVOLVING ABOI Apheresis technique used:
Specific columns used for IA are more efficient with fewer side effects than nonspecific columns but costly and number depend on center protocol and titer of antibodies.
Patient with low titer still there is controversy about needing apheresis or not. Role of rituximab:
The use of RTX reduces the risk of isoagglutin rebound and the risk of ABMR but removed by PEX. Utility and role of IVIG:
IVIG administration reduces the antibody rebound after transplantation and the risk of ABMR may be used one day before TX or with PEX. Method to detect isoagglutinins quantity
flux cytometry is the best even if the method has a high cost. The tube and gel techniques also used. Type of immunosuppression
The basal immunosuppression begins together with the desensitization but steroid withdrawal has high incidence of rejection. Utility of post-transplantation apheresis
With rebound and graft dysfunction. Accommodation
Accommodation :the presence of circulating isoagglutinins and antigens on the graft cells with normal renal function and normal histology with or without of C4d. Principal complications:
ABMR is the first cause of graft loss in transplantations involving ABOi
Some bleeding which reflect mainly effect of PEX or IA. KPD:
Base on a single center strategy, on a regional strategy on a national or international strategy. Cheaper than desensitization.
Decrease time on waiting list and provide good compatible donor. CONCLUSION:
Overall ABOi kidney transplantation has many benefits and allow many chances for Recipients on waiting list specially with PKD.
With good graft and patients survival.
But still no randomized control trial to ensure or prefer one protocol over others.
Need more clinical trials specially with low immunosuppressive protocols and desensitization to avoid infections and malignancy.
Mohamad Habli
3 years ago
Kidney transplantation is the treatment of choice for patients with end stage renal disease.
Sensitized patients and patient with ABOi pairs wait for long time to get appropriate kidney offer.
Two major strategies evolved to overcome the immunological risk.
1- Paired kidney exchange program
2- Desensitization and transplantation against ABO system.
Overview of desensitization — The overall goals and purpose of ABO desensitization are to lower the immunogenicity of the incompatibility to allow for successful transplantation with commonly used induction and maintenance immunosuppressive regimens. Although there is no uniformly accepted ABO desensitization protocol, most commonly used protocols employ a combination of the following strategies:
●Removal of circulating ABO antibodies, typically with extracorporeal methods such as plasmapheresis or immunoadsorption
●Immunomodulation of the recipient immune system, typically with intravenous immune globulins
●Depletion of the B cell population responsible for ABO antibody production, most commonly with the anti-CD20 agent rituximab
Removal of circulating ABO antibodies – The two most commonly used methods of antibody removal are plasmapheresis and immunoadsorption, with the goal of achieving titers ≤1:8 to 1:32.
Immunomodulation — IVIG is to replace immunoglobulins that are removed with plasmapheresis or immunoadsorption. In addition, IVIG may also block Fc receptors to prevent a rebound in anti-A/B antibody titers when the plasma cells have naked receptors and, therefore, are stimulated to make more antibody.
B cell depletion —Rituximab, a humanized mouse monoclonal antibody that targets CD20 (expressed on the majority of B cells), is the most commonly used agent. Splenectomy, which was historically used for this purpose, is no longer used in most countries. Despite an absence of detectable splenic B cells after rituximab administration, plasma cells remain as the majority of plasma cells lack CD20 receptors. The specific dose of rituximab required in this setting is unclear. Rituximab is given four weeks prior to the scheduled transplant surgery date.
Immunosuppression Apart from desensitization, the immunosuppression in kidney transplantation with ABOi is similar to that used for standard transplantation which includes CNI based triple therapy namely TAC/MMF/PRED.
Post-transplantation apheresis Apheresis treatments post-transplantation are reserved for patients who present abnormalities of graft function together with isoagglutinin rebound. Antibody rebound is expected in 2 weeks following transplantation, and not associated with histological signs of AMR.
Accommodation-Accommodation in renal transplantation involving ABOi has been defined as the presence of circulating isoagglutinins and antigens on the graft cells with normal renal function and normal histology.
Role of protocol biopsies
The presence and the role on protocol biopsies of C4d in transplantations involving ABOi seems to be related to accommodation when found in the absence of clinical or other histological abnormalities.
In conclusion, ABOi renal transplantation is evolving because of the reconditioning strategies available and good outcomes comparable to the ABOc transplants on the long term followup.
MOHAMMED GAFAR medi913911@gmail.com
3 years ago
ABOi kidney transplantion is chalenging , using different startigies to reach safe point at which the patinet can be transplanted is not easy.
Different stratiges to reduce both anti A&B antibody titre to a level at which the trasnplant can go safely with minimal comaplications .
TECHNIQUES OF ABO DESENSITIZATION ,
Removal of circulating ABO antibodies ,by PLEX OR IA to reduce titre level between 1:8 to 1:32
Immunomodulation ,by IV IGG , using high dose befor transplantion
B cell depletion ,in the past they was using splenectomy no surgical splenectomy has been replaced by RTX.
Transplants involving ABOi compared to those involving ABOc had a significantly higher mortality rates at 1, 3 and 5 years .
graft losses and mortality in transplants involving ABOi became equivalent to ABOc transplants at 8 years after transplantation.
KPD programme is now the choice for pt who are highly sensitized with living non matched or ABOi , as the programme rapidly growing now around the globe , the ABOi transpalntion had decreased signifcantly.
Mohamed Mohamed
3 years ago
IV. Current protocols and outcomes of ABO-i incompatible kidney transplantation Summarise this article
Introduction The use of ABO- renal transplantation is increasing in this century with the increase in our knowledge of the immunological barriers & the advent of new drugs.
The main historical steps in the evolution of desensitization are:
1. 2004: Takahashi et al IA or PP 2-3 times before transplantation Splenectomy 441 transplants
2. 2005: Gloor et al PP,IVIG & anti-CD20 before transplantation No splenctomy 11 transplants
3. Genberg et al IA & anti-CD20 before transplantation LMW heparin No splenectomy 15 transplants
Currently different combinations of the following are used in ABO-i transplantation:
1. IA or PP for removal of ABO antibodies. Started day to weeks prior to transplantation to achieve an acceptable A/B titers (1:8 to 1:32) The number of sessions for both PP & IA differ depending on the baseline antibody titer. PP is simpler & cheaper than IA It removes 20% of antibodies/session S/E include removal of protective antibodies & coagulation factors leading to infections & hemorrhages. Different techniques of IA allow more selective removal of antibodies & less side effects, though with extra costs. =========================================== 2. High dose of IVIG to replace immunoglobulins lost by PP or IA. Mostly given as single dose of 500 mg IVIG/kg BW on the day before transplantation. It can also be given in 2 divided doses -4 & -1 days before transplantation. ========================================= 3. Anti-CD20 Rituximab has largely replaced splenectomy for B cell depletion. The dose is generally 375 mg/m2; its major effect is between 3 week & 6 months. ========================================= 4. Immunosuppression: Similar to that used for standard transplantation. Started together with the desensitization. Reduction of immunosuppression is generally not allowed in ABO-i transplants.
Significantly higher mortality rates at 1, 3 & 5 years in ABO-i vs ABO-c transplants. Graft losses & mortality are equivalent in both groups at 8 years after transplantation. The higher mortality rate is related to the intense of IS therapy. PP & IA also induced more coagulation disorders in ABO-i. transplants. Another way to overcome immunological barrier is enrolment of ABO-i recipients into PKD programs, or a combination of PKD & desensitization to reduce complications.
Abdul Rahim Khan
3 years ago
This review article describes different protocols and outcome of ABOi – KT.About 30 % patients awaiting a renal transplant are considered incompatible from immunological perspective because of Anti HLA antibodies of ABO incompatibility. There are two options to overcome these barriers:
1-Desesitization
To remove antibodies from recipient and modify immunological response so that transplantation can be made feasible
2- Paired kidney exchange
To exchange organs between two or more pairs to exchange between different donors.
Immunological aspects
ABO glycoproteins are expressed on RBC, endothelial cells and epithelial cells. in kidney these are expressed on Collecting and distil tubules and vascular endothelial cells. ABO blood group system has 4 categories including A,B,AB and O. Blood group O have high antibody titres against A and B. So recipients of blood group O have higher chances of ABMR. Circulating epitopes A and Blinked to VW factor when free can cause ABMR. In ABOi – KT better results are achieved when transplanting kidneys from A2 donors to O recipients.
Desensitization Protocols
Plasmaphresis (Pp) or immune adsorption
To remove circulating ABO antibodies . Target is to lower the antibody titres between 1:8 to 1:32.
Immuno Modulation-
IVIG replace the immunoglobulin lost during PP-It also blocks Fc receptors and causes immune regulation.
B ell depletion-
Using Rituximab- it blocks CD 20 receptors on plasma cells- Medical Splenectomy has now replaced surgical Splenectomy.
Accommodation-
This process decreases the risk of rejection by tolerance and low affinity of antibodies and by blockage of compliment activation
Immunosuppression will involve induction with either ATG or Basiliximab and maintenance with TAc, MMF and prednisolone. There is higher risk of AMR in ABOi – KT and its costly treatment . ABOi – KT can be complicated by infections and bleeding as clotting factors are lost in PP.
Out come of ABOi – KT
Outcomes in ABOi – KT at 1, 3 -5 years are low as compared to and ABOc -KT.
Significant increase in AMR in in ABOi – KT but not much increase in cell mediated rejection.
Heba Wagdy
3 years ago
ABOi kidney transplantation and KPD are the 2 main strategies to overcome shortage of deceased donor organs and to allow patients with advanced age, cardiovascular disease and immune reactivity to avoid long waiting time on dialysis. Immunological aspects:
ABO system antigens are expressed on RBCs, tubules and vascular endothelium.
Group O patients have higher anti-A/B antibody titer causing higher incidence of AMR post transplant while kidneys from A2 donors to O recipients show better results. Development of the practice of kidney transplantation in ABOi pairs:
ABOi was a contraindication for kidney transplantation.
However, ABOi transplants increased worldwide due to
Improvement in diagnosis and treatment of AMR
Excellent results of ABOi transplants in Japan
The use of rituximab instead of splenectomy.
The outcomes of ABOi transplants were similar to those with standard risk.
Techniques of ABO desensitization and different protocols used: Removal of circulating ABO antibodies:
Plasmapheresis (PP) is cheaper, simpler but less effective, it removes 20% of antibodies per session with removal of protective antibodies and coagulation factors.
Double filtration PP is safer than PP as allow smaller molecules to return back to the patient.
IA selectively remove humoral factors with removing of ABO agglutinins. Immunomodulation:
High dose of IVIG used to replace immunoglobulins lost with apheresis techniques in addition to its immunoregulatory effects to decrease antibody rebound and risk of AMR. B cell depletion:
Now rituximab replaced splenectomy to obtain B cell depletion to decrease agglutinin titer to predetermined level.
Protocols used are mixture of those strategies with several attempts made to reduce associated complications and costs. Clinical outcomes:
Studies involving ABOi transplants are generally with low number of patients.
A systemic review examined 83 studies highlighted the efficacy of rituximab and IA but was limited by absence of randomized controlled trials.
A more recent and wider systemic review showed that ABOi transplants have significantly higher mortality rates than ABOc transplants at 1,3 and 5 years, mostly due to intense immunosuppression causing severe infections. Open controversies in ABOi kidney transplants:
Apheresis technique used, type of IA, number of apheresis treatments and its role in patients with low isoagglutinin titer.
Role of rituximab is not well determined and seems to be unnecessary in some patients.
The method of administration of IVIG is either single dose or divided doses to avoid possibility of administration of isoagglutinin with IVIG
Isoagglutinin quantification to determine the immunosuppression and apheresis techniques. However, its predictive value for AMR is low.
The effect of steroid withdrawal either early or low is not well studied.
Post transplant apheresis, some authors said it has no beneficial effect without graft dysfunction while others do it in patients with isoagglutinin rebound or with high basal levels of antibodies.
Accommodation:
It is lack of rejection in presence of circulating ABO antibodies with normal kidney function and normal histology.
It is facilitated by reduction of isoagglutinin levels, blocking of complement activation and rituximab. Role of protocol biopsies:
It may show C4d deposition and seems to be related to accommodation when present in absence of clinical and histological abnormalities. Complications:
Hemorrhage is more common in ABOi transplants, significantly associated with number of IA sessions.
Infectious complications have different incidence in different studies mostly vary according to intensity of desensitization.
AMR, the main cause of graft loss, related to level of isoagglutinin level at transplantation and presence of anti-HLA antibodies. KPD:
2 pairs of donor and recipient with ABOi exchange the kidneys and may include higher numbers of pairs. Making a choice between desensitization and KPD
KPD is cheaper but may be associated with prolonged waiting time.
Costs of KPD is similar to ABOc kidney transplants
According to data from US, overall KPD is increasing while desensitization strategies are decreasing.
Abdulrahman Ishag
3 years ago
IMMUNOLOGICAL ASPECTS;
The ABO blood groups consist of four categories (A, B, AB and O). The formation of anti- blood group antibodies occurs against the antigens that are not native to the host. Group O individuals have higher antibody titers to both the A and B antigens.
The antigens of the ABO system are glycoproteins expressed on erythrocyte membranes as well as on epithelial and endothelial cells. In the kidney these glycoproteins are also expressed on the collecting and distal tubules and on the vascular endothelial cells.
In addition to the membrane-linked antigens, circulating epitopes A and B, both soluble and linked to von Willebrand factor exist in some patients. These antigens, when free, are responsible for ABMR .
The A2 subtype does not have circulating antigens linked to von Willebrand factor . Indeed, better results in transplantation involving ABOi are obtained when transplanting kidneys from A2 donors to O recipients.
TECHNIQUES OF ABO DESENSITIZATION AND DIFFERENT PROTOCOLS USED OVER TIME;
1-Removal of circulating ABO antibodies;
The removal of circulating ABO antibodies is obtained principally by plasmapheresis or immune-adsorption (IA).
Plasma exchange;
The simpler, cheaper, but less effective technique .The procedure eliminates approximately 20% of the antibodies by session. Additionally, removes protective antibodies and coagulation factors.
Immune-adsorption (IA).
Made by the use of columns for the selective removal of humoral factors by IA. There are different types of columns for IA . IA with immobilized antibodies: are the most widely used.
2-Immunomodulation;
This technique consists in the administration of high doses of polyclonal intravenous immunoglobulin (IVIG) to the patient before transplantation.The aim is to replace the patient’s immunoglobulins lost because of apheresis techniques. In addition, IVIG blocks the Fc receptor and has immunoregulatory properties.
3-B cell depletion;
To date, RTX, a humanized monoclonal antibody that binds to CD20 expressed on the B cell membrane, is the drug used to obtain B cell depletion.
CLINICAL OUTCOMES AFTER RENAL TRANSPLANTATION INVOLVING ABOI;
Overall, transplants involving ABOi compared to those involving ABOc had a significantly higher mortality rates at 1, 3 and 5 years. The higher mortality rate is probably a consequence of the high immunosuppression related to the therapy. Indeed, some studies in which selected patients received a lower, tailored desensitization therapy reported an improved survival rate, with fewer infections and without ABMR.
Complications;
1-Surgical complications in transplantations involving ABOi are similar to complications of standard transplants, with the exception of hemorrhages.
2-ABMR is the first cause of graft loss in transplantations involving ABOi.
KPD ;
The simplest model of the KPD is the two-way, in which two pairs of donors and recipients with ABOi exchange the kidneys, thereby resolving the incompatibility.
A variant of domino KPD is the Never Ending Altruistic chain,which allows a higher number of recipients to be transplanted by the use of bridge donors .
KPD programs have several points that yet need to be better clarified. The principals are as follows:
1-Transportation of kidneys vs donor travel:
The travel of the organ minimizes the costs and allows the continuity of donor care.
2- Simultaneous vs no simultaneous exchanges:
The drawback of simultaneous donations is logistical, principally if multiple organ donors will be operated on in the same center.
3-Closed chains vs open chains:
The channels of transplantations initiated by a non- directed donor may be extended but should end with donation to a recipient on the waiting list.
MAKING A CHOICE BETWEEN DESENSITIZATION AND KPD;
KPD is generally cheaper with respect to desensitization, it remains to be answered the availability of KPD in a short time.
The costs were obviously higher in the case of ABOi transplant and evaluated in $ 65080 per transplant episode vs $32039 per transplant episode for ABOc transplant.
Ben Lomatayo
3 years ago
Introduction
Renal transplantation is the best form in renal replacement in patients with ESRD. However many patients cannot be transplanted due organ donors shortages and there remain in the waiting list time or die. Another problem is ~30% of recipients are incompatible with their donors because of either HLA antibodies or ABO antibodies[1] Th two suggested solutions to cross these immunologic barriers are desensitization and paired kidney donation. This review provides overview of ABOi-KT, techniques of ABOi-KT and its outcomes.
Immunological Aspects
The ABO system antigens are glyco-proteins expressed on RBCS, as well as endothelial cell, tubuli,and glomeruli. Blood type O people have higher levels of anti A/B antibodies and therefore, they are at higher risk of AMR[3]. Better outcomes are seen when A2 donated to O patients. A2 doesn’t have circulating antigens linked to von Willebrand factor[5]
Development of practice of Kidney Transplantation in ABOi-pairs
This was absolute contraindication to Tx
First report A2 to O by Brynger et al [10,13]
Practice evolved from 1998 to 2000 in Japan( splenectomy), US(RTX) , and Europe(Sweden) = AI
Techniques of Desensitization and different protocols used over time
Removal of circulating ABO antibodies
Plasma-phersis – 20% reduction in antibodies per session
Double filtration plasma phersis
Immune-adsorption – specific columns AI(more efficient) & non- specific AI[20]
Immuno-modulation
High dose IVIG before Tx to replaced immunoglobulins plus immuno-modulatory properties
B cell depletion
Splenectomy(historical)
Rituximab
B cell depletion facilitate accommodation ; the graft is resistance to injury in the presence anti A/B antibodies. This status is usually acquired after 2 weeks of transplantation even if the titer of anti A/B antibodies is high[21,22]
Clinical outcomes After ABOi-Tx
The main problem is lack of RCTs
Report from recent systemic review of observational studies demonstrated inferior outcomes in ABOi-rTX compared with ABOc-rTX (higher mortality rates and graft loss at 1,3 years). Outcomes patient and graft survivals were the same after 5 years[44-47]
Open Conservatories in ABOi-rTX
This is mainly about desensitization strategies e.g aphersis technique, role of RTX, utility and use of IVIG, methods of measuring iso-aggulitinins, postTX aphersis, Accommodation, protocol biopsies, complications, type of immune-suppression
PKD
First report about this by Rapaort 1986[85]
The idea is to exchange donors who are incompatible so that they compatible now and the transplant proceed[86-88]
This can be two way, three way and so forth[89]
Can be achieve by the domino KPD ot the Never Ending Altruistic chain[96-98]
PKD should always be tried before desensitization
Conclusion
Now days ABOi-rTX became feasible due proper understanding of immune system and more refine desensitization technique.However there are still many unanswered questions conserning desensitization techniques. ABOi-rTX are expensive compared to ABOc-rTX , how ever they are less expensive than dialysis. For this reason PKD was introduced and it became a valid option. The problem is PKD is limited by legal and ethical considerations. Unfortanetly only ~ 31% of pairs make successfully through PKD donors
Manal Malik
3 years ago
Summary of Current protocols and outcomes of ABO-incompatible kidney transplantation
of this this review is describe the more recent data from literature on different protocol used and clinical out come of ABOi-KT .
30% of transplantation is incompatible.
Two ways to over come barrier for ABOi-KT :
1-desensitization to remove antibodies.
2-paired kidney donation between 2 paired or more.. IMMUNOLOGICAL ASPECTS
The antigens of the ABO system are glycoprotein expressed in RBCs ,epithelial and endothelial cells and kidney (tubules &vascular endothelial).
Presence of epitopes A&B both soul able and linked to von will brand factor existed in some patients these antigens where free are responsible fo ABMR.
Presence of c4d proof that there is reaction between antigens of the ABO group induce complement activation. TECHNIQUES OF ABO DESENSITIZATION AND DIFFERENT PROTOCOLS USED OVER
There are different ways to achieve desensitisation with ABOi transplantation: 1-Removal of ABO antibodies and this through two method
Plasmapheresis
Immunoadsorption Plasmapheresis simpler and cheaper but less effective and removal of protective antibodies and coagulation factors. Immunoadsorption 1A2 different type
1-1A immobilized antibodies effective in removal IgG antibodies.
2-immoblized staphylococcal protein A removal of IgG with different classes. 2-Immunomodulation
High dose of polyclonal IVIG given to before patient before transplant aims to replace the patient immunoglobulin loss in apheresis technique .also blocks the FC receptor (immunoregulatory properties). 3-Bcell depletion
Rituximab humanized antibody bind to CD20 express on B cell membrane .
Is used to reduce agglutation titre level. CLINICAL OUTCOMES AFTER RENAL TRANSPLANTATION INVOLVING ABOi
Wide systemic review end with different results
Overall ABOi -KT compared to ABOc had signific higher mortality rate at 1,3,and 5.
Graft loss and mortality in ABOi equivalent to ABOc -KT at 8year after Transplant.
Higher mortality rate related to high immunosuppression therapy cause sever viral and bacterial infection.
Coagulation disturbance induced by plasmapheresis or 1A.
Higher dose of rituximab result in infection such as polyoma virus nephropathy
Technique of apheresis
Column used for 1A
1- Specific column which is more efficient and fewer side effect.
2- Nonspecific less efficient and lower cost.
Numbers of apheresis treatment differ depend on level of
Isoagglutinin and the center.
Patient with low titre isoagglutinin plasmapheresis help in reduction of inflammatory molecules. Role of RTX
Use of rituximab has allowed avoidance of splenectomy since 2002.
Use of RTX reduce the risk of isoagglutinin rebound and risk of ABMR and risk of chronic rejection.
Dose 375mg/m2 it major start 3 to 6 week after administration.
RTX begin 1 month before TX.
Avoid plasmapheresis after RTX(may be removed)
. IVIG
Mechanism of IVIG that modulate immune reaction are:
(1) Blockage of the Fc receptor on the leukocyte membrane.
(2) Inhibition of the complement activation.
(3) Inhibition of circulating antibodies against HLA. Isoagglutinin quantificationhas
Flux cytometry s used to know isoagglutinin titre is high cost has low predictive value before desensitisation and postTX titre. Immunosuppression
Immunosuppression in kidney transplant with ABOi is same as that used for standard TX. Post-transplantation apheresis
Apply for patients with :
abnormal graft function with isoagglutinin rebound. Accommodation
Is defined as presence of circulating isoagglutinin and antigens on the graft cells with normal renal function and normal histology..
Presence of low titre of antibodies with low affinity and with blockage of complement activation will explain accommodation.
Eculizumab may facilitate accommodation
. Complications
Bleeding related to number of apheresis treatment
Infection related to desensitisation
ABMR is first cause of graft loss in TX ABOi KPD
KPD in the two ways in which 2 paired of donor and recipient with ABOi exchange the kidney so resolve incompatibility .
KPD can be national and an international program.
KPD programs have several points that yet need to be better clarified. The principals are as follows:
1-Transportation of kidneys vs donor travel.
2-Simultaneous vs no simultaneous exchanges.
3-Closed chains vs open chain. CONCLUSION
ABOi barrier have been over come successful of ABOi KT refer to:
1- Accommodation.
2- Humoral tolerance.
3- desensitisation .
4- removal of isoagglutinin.
5- Immunoadsorption and antiCD20.
ABOi-KT more costive than ABOc-KT.
Presence of wide national registry in future will increase the number of transplantation.
.
Ibrahim Omar
3 years ago
Summarise this article :
this review describes the different protocols and the clinical outcomes of ABO-incompatible kidney transplantation.
30% of living donors are immunologically incompatible either due to anti-HLA antibodies or ABO antibodies. together with the increasing shortage of kidney grafts, some transplantation centers have successfully tried to do ABO incompatible kidney transplantation (ABOi-KT).
there are 2 main methods for managing ABOi-KT :
1- desensitization with some variable protocols to remove antibodies and prevention of their rebound after transplantation.
2- paired kidney allocation by exchange of organs between 2 or more pairs. it is world-wide evolving but it has managed only 31% of pairs. however, this number can be increased if wide national registry would be used instead of smaller registries.
the current methods for desensitization include the following :
1- apharesis : it has been largely improved in recent years. however, several questions remain regarding the best techniques to be used. 2- IVIG : it acts by replacing the immunoglobulins lost with apharesis. also, it has immunoregulatory properties by blocking Fc receptors. 3- Immunoadsorption. 4- Rituximab : by blocking CD20 on plasma cells. it has replaced splenectomy.
regarding the outcome, many reports document outcomes similar to standard translantation.
there are 2 main mechanisms responsible for successful ABOi-KT :
1- accommodation : it means stable graft functions despite the presence of circulating antibodies and antigens on graft cell surface. presence of C4d on peritubular capillaries was added to the definition of accommodation on 2006. 2- humoral tolerance : it is an area on active research.
Ban Mezher
3 years ago
Transplantation is the treatment of choice for patients with ESRD, but shortage of deceased donor pool in addition to advance age, immunological activity or CVD are a big obstacles. So live donor a good alternative, but ~30 of patients on waiting list were sensitized. To overcome this there are 2 options:
desensitization
PKD program
ABO Ag expressed on RBC & on epithelial cells & endothelial cells. Blood group O Ag had the highest Ab titer against A & B Ag, so patient with blood group O had high risk of ABMR after ABOi-T. Circulated soluble epitopes of A & B Ag when be soluble can be linked to von-Willberand factor & cause ABMR, but A2 Ag didn’t have these soluble epitopes result in good result of ABOi-T.
ABOi-T became a good option for sensitized patients. Desensitization protocols involve combination of following techniques:
Removal of circulating ABO Abs: by PP( removing of all plasma proteins , cheap, & remove ~20% of Abs by a session) or IA( effective in removing IgG, specific IA remove only undesirable Abs.
Immuno-modulation: by giving high dose IVIG before transplantation , it can replace lost immunoglobulin by PP & block Fc receptors .
B cells depletion: used to reduce iso-agglutininAbs , traditionally done by splenectomy, but now replaced by anti-CD20( rituximab).
Combining of PP or IA with IVIG & rituximab show comparable result at 3 years between ABOi-T & ABOc-T.
Desensitization regimes are costly, so to reduce the cost :
use low dose of rituximab
rituximab free regime
reduce IA session according to baseline ABO Abs titer( on demand strategy)
use combination strategy according AB titer ( Ab titer of 8 use only rituximab, Ab titer 16-24 use PP+ rituximab, A b titer >64 use IA + rituximab)
The result of different studies show good result of both patient & graft outcome in ABOi-T, after 8 years post transplant, but there were increased mortality & BK virus infection in 1,3, & 5 years due to aggressive immunosuppression.
Multiple controversies of ABOi-T as:
Techniques of aphaeresis; specific column IA had high effeciency with low side effects but high cost while non specific column IA had less cost with lower efficiency. Number of aphaeresis session depend on baseline titer of ABO Abs.
Role of rituximab: not necessary in all patients. It used to reduce Abs rebound , ABMR & chronic rejection. Its effect occur between 3 weeks-6 months.
IVIG: reduce AB rebound & ABMR. Its dose 500mg/kg given a day before transplantation.
Iso-agglutinin qualification: tube & gel methods are widely used, but best method is flux cytometry with high cost.
Immunosuppression : use the same triple regime of ABOc-T
Post transplant aphaeresis: used for patient with graft dysfunction with rebound increase in Ab titer ( no benefit in absence of graft dysfunction)
Accommodation: it occur due to low titer antibodies , low affinity & blocking of complement activation.
Role of protocol biopsy: show positive C4d without evidence of AMR which is related to accommodation.
Complications: surgical complication were similar in both ABOi-T & ABOc-T, but higher hemorrhage & BK virus infection among patients with ABOi-T.
It is difficult to decide which option is used for ABOi-T ( desensitization vs PKD ). Now Single center & regional exchange increase the facility of PKD with dropping of desensitization.
Doaa Elwasly
3 years ago
Transplantation of living donor is an option to avoid long term dialysis hazards but obstacles are faced including immunological barrier,which could be HLA and or ABO incompatibility , in order to solve this problem 2 strategies are applied which are desensitisation and paired kidney exchange program. The most frequent protocols applied to obtain desensitization in pairs with ABOi are a combination of those strategies which are Removal of circulating ABO antibodies
Using plasmapheresis or immune-adsorption (IA) and apharetic technique which is the most updated technique in order to lower the circulating anti-A/B antibody levels to reach titers between 1:8 and 1:32.
-plasma pheresis eliminates 20% of Ab in a session along with coagulation factors and protective Ab.
-double filtration plasmapheresis allows return of essential components to the blood there by avoiding PP drawbacks.
-IA selectively eliminates humoral factors using immobilised Ab or immobilised staph protein A or immobilized antigens and synthetic epitopes Immunomodulation
Using IVIG having immunomodulatory role and replacing Ig lost in apheresis B cell depletion
Using splenectomy which is currently replaced by Rituximab
Accommodation can occur protecting the kidney on the long term because by lowering ABO Ab titer graft can gain within 2 weeks a capacity to resist complement damage.
Genberg et al study mentioned that ABO incompitable transplant cases treated 30 days before transplantation with IA and Rituximab and IVIG one day before transplantation showed no significant difference between ABO compatible and incompatible groups regarding patient , graft survival and rejection.
Another study stated that stopping IA can cause rebound increase in Ab titer
The generally applied strategy is using Rituximab 10 days before Transplantation(Tx) and plasma pheresis /IA 1week before and after Tx along with 2 doses of IVIG prior Tx
Other policies used to lower Rituximab dose or decrease IA frequency with acceptable outcomes, concluding that individualising desensitisation has favourable net results. Clinical outcomes after Renal Tx of ABOic cases
ABOi c Tx showed comparable outcomes to ABO c Tx but this was concluded from studies done on small number of cases
2 studies were done with bigger number of patients mentioned that Rituximab and IA have great efficacy but these studies had limitations.
More studies are needed to detect best protocols for cases with low pretransplant anti-ABO antibody titers
According to Anti A /B Ab titer desensitisation protocols are
If Ab titer <8—–induction and maintenance therapy
If 8 —-Rituximab— induction and maintenance therapy
If16-64—-Rituximab +DFPP—- induction and maintenance therapy
If>264—-Rituximab+IA—- induction and maintenance therapy
Mortality rate is higher in ABO ic Tx than ABO c Tx at 1,3 ,5 years could be due to extensive immunosuppression , coagulation disorders and infectious complications ,while graft loss and mortality is equal in both groups at 8 years post trasnplanation Controversies in ABO ic Tx Technique of apheresis
The high cost of specific columns used because it is efficient than other columns lead to reusage of those specific columns
It seemed that apharesis could be benefical even in cases with low Ab titers to decrease inflammatory molecules level RTX role
It replaced splenectomy , it lowers the risk of isoagglutin rebound , the risk of ABMR and the risk of chronic rejection. IVIG
It blocks FC receptor on leucocytes, inhibit complement activation and HLA Ab, also it decreases Ab rebound after Tx ,decreasing ABMR risk Isoagglutinin quantification
Detected by flux cytometry , tube and gel technique .
On the other hand it has no predictive value for ABMR. Immunosuppression
For ABO I cases is the same as for standard transplantation. It starts with the desensitization. Post-transplantation apheresis
Is done for patients with abnormalities of graft function and with isoagglutinin rebound Accommodation
Is the presence of circulating isoagglutinins and antigens on the graft cells with tolerance and less rejection risk due to due to the presence of a low titer of antibodies, with low affinity and with the blockage of complement activation.
Eculizumab can enhance accommodation. Protocol biopsy role
C4d presence in grafts of ABOi Tx can be related to accommodation in the absence of clinical or other histological abnormalities Complications
Surgical complications is the same for ABO incompatible and compatible Tx except hemorrhage is more common in ABO ic group due to aphaersis , number of IA done
Infection complication is dependent on desensitsation policy
ABMR risk varies according to the isoagglutinin level at transplantation and the presence of anti HLA Kidney paired donation (KPD)
It includes 2 ,3 ,4 way and so on
Domino KPD allows a higher number of recipients to be transplanted by the use of bridge donors
Some issues are highlighted :
-transport of door versus the organ
-Simultaneous versus non simultaneous exchange
– Closed chains vs open chains
National Kidney Registry in the United States, revealed that KPD is increasing , while the desensitization strategy is decreasing
Sherif Yusuf
3 years ago
Blood group antigens are present not only in RBCS but also in the endothelial cells and they include A, B, AB, O
Patient with blood group A has antibodies against B antigen, while those with blood group B has anti -A antibodies
Individuals with blood group O has no antibodies so they are universal donors, on the other hand, patients with blood group AB are universal recipient.
Blood group A is subdivided into A1 and A2. A2 antigen is less common accounting for 20 % of white race individuals with blood group A, and is less expressed on RBCS than A1 so recipients with anti-A sera ( those with blood group B, O) can receive kidneys from donors with blood group A2 if anti-A sera is low. In other words individuals with blood group A2 can serve as universal donors but only if the titer of antibodies is low
Desensitization protocol
1– B cell depletion
Using either splenectomy which now is replaced by rituximab due to its side effects including infection with encapsulated organisms and surgical complications
Rituximab produce splenic B cell depletion thus decrease the risk of rebound, but the problem that it spares plasma cells since they contain no CD20 receptors, thus its benefit till now is uncertain
In order to reduce the cost, multiple attempts were done to reduce the number and the dose of Rituximab or remove it from desensitization protocols or give it only on demand ( if titer > 1/16) with a good outcome.
Only 35% of desensitization protocols are using Rituximab
Rituximab takes 3-6 weeks in order to exert its full effect
One protocol is to give 1 dose of Rituximab 375 mg/m2 30 days before transplantation
2– Antibodies depletion
Plasmapheresis (remove 20 % of antibodies per session), less effective, remove also coagulation factors leading to bleeding tendency
Double filter plasmapheresis, has fewer complications than conventional plasmapheresis, as a second filter is used which allows for the return of small molecules
Immunadsorption IA which is a specific technique that selectively removes IgG with the least side effects (produce 2-4 fold titer reduction per session), but more expensive ( 2-3 times more than plasmapheresis)
Antibody depletion usually is assessed 2 weeks before transplantation , the indication and the frequency depend on isoagglutinin titer at that time, 1 session of PE can decrease the titer by one dilution so the number of sessions required can roughly be known
The goal is to achieve isoagglutinin titer of ≤1:8, in patients with initial low titer benefit of plasma exchange is debatable
3– IVIG
IVIG is usually given after plasmapharesis, but one regimen is to give 0.5 gm/kg in 1 dose the day before transplantation or in 2 doses 4 and 1 day before transplantation
It acts as an immunomodulator by blocking Fc receptors , so it prevents the rebound increase in antibody by plasma cells, moreover IVIG aid in the replacement of immunoglobulins that are removed during PE or IA
Immunosuppression
Induction using either basiliximab or ATG according to other risk factors
Maintenance using CNI better tacrolimus, MMF, and steroids (steroid withdrawal is not recommended)started 2-7 days before transplantation, steroids
Monitoring
Monitoring is very important since there is a high possibility of a rebound increase in antibodies post-transplantation with a risk of ABMR especially in the first week
3 techniques are used : tube, gel and flowcytometry
There is inter-lab variability, the most sensitive is Flowcytometry but the problem is the cost and availability, followed by gel then tube technique
Monitoring of isoagglutinin titers daily till discharge form the hospital, then 2-3 times per week for the first month then weekly till 3 m post-transplant then annually
If posttransplant isoagglutinin titer increases, the patient should be considered for renal biopsy (especially if there is renal dysfunction) and for preemptive plasmapheresis
Outcome
ABO-incompatible transplantation is associated with lower patient survival at 1, 3, and 5 years post-transplantation but long term patient survival at 8 years is comparable to ABO compatible transplantation, this may be attributed to the increase in the risk of infections and sepsis including pneumonia, UTI, wound infection, PCP, CMV and BK virus, also bleeding complications related to coagulopathy induced by plasmapharesis
There is a significant increase in the risk of ABMR but not acute CMR in patients with ABOi transplantation with subsequent reduction in graft survival. Diagnosis requires both the presence of histological features of ABMR and the presence of antibodies, C4d can be present in biopsy with no features of ABMR ( due to accommodation) thus the significance of C4d standing is less in ABO I transplantation
Complications
Bleeding is the most common surgical complications related to ABO I transplantation due to removal of clotting factors by plasmapharesis
There is an increase in the risk of infections and sepsis in ABOi when compared to compatible transplantation
There is significant increase in the risk of ABMR but not acute CMR in patients with ABOi transplantation
Cost
ABO I transplantation is expensive
Riham Marzouk
3 years ago
Transplantation from ABO incompatible donor became safe and available in order to increase donor pool and decrease waiting time to stay on dialysis and to shorten the waiting list of NDD and DCD.
ABO antigens are glycoproteins expressed on RBCs, epithelial and endothelial cells. They are 4 groups; A, B, AB, and O.
A group has A antigen and anti-B antibody, B group has B antigen and anti-A antibody, AB has A and B antigen and has no antibody, O group has no antigen and has anti-A and anti-B antibodies.
A group has two phenotypes A1 that is more antigenic and A2, which resemble O group, has no antigens.
In the renal system, ABO expressed on distal and collecting tubules and vascular endothelial cells, when expressed heavily, it is responsible for acute rejection attack.
The reaction of antibody or isoagglutinins with these glycoproteins will lead to complement activation and c4d deposition.
The first trial of transplantation from ABO incompatible donor was done in Japan.
TECHNIQUES OF ABO DESENSITIZATION AND DIFFERENT PROTOCOLS USED OVER TIME:
1- Removal of antibodies by apheresis ; plasma exchange with high permeable filter is less cost, available to remove antibodies by 20% every session, the main concern is its complications as it is non selective removes also clotting factors and other antibodies, so we can do plasmapheresis using double filter as the second filter allows the return of small important molecules try to avoid the complications, also we can use another adding filter or column to selectively IgG which is called immunoadsorption to avoid complications of removal of all antibodies.
2- Immunomodulation using IVIG post plasmapheresis session to replenish the removed beneficial antibodies.
3- Rituximab antiCD20 antibody, is medical splenectomy, it depletes B cells, which are responsible for antibody production.
There is no standard protocol for desensitization prior to transplantation, but in general, we can give rituximab 2 weeks prior to transplantation and do plasmapheresis 4 sessions 1 week before operation and continue it for another 3-4 sessions post transplant, tacrolimus ,MMF and steroid were given from 2-7 days prior to transplantation, keeping trough level of tacrolimus from 12-15 ng/ml.
CLINICAL OUTCOMES AFTER RENAL TRANSPLANTATION INVOLVING ABOI
Mortality in the patients transplanted from ABO incompatible donor is higher at 1, 3 and 5 years post-transplant than the patients transplanted from ABO compatible donor, this mostly related to side effects of heavy immunosuppression given to these patients like infections either bacterial and viral like BK virus, coagulation side effects.
Accommodation:
C4d deposition in absence of any signs and symptoms of AMR, so, this because of accommodation of the graft to that level of antibodies without making graft injury.
KPD program is another solution to enlarge donor pool versus transplantation from ABO incompatible donor, and the choice depends on many factors related to the center or hospital itself, availability and the cost.
Thank you Riham They mentioned giving Rituximab 2 weeks prior to transplantation, in fact, we give it in the UK 3 to 4 weeks prior to transplantation. Do you know Why?
B cell depletion takes 1-6 weeks to be completed, so given earlier
A. Nicholas R. Barnett, Vassilis G. Hadjianastassiou, Nizam Mamode. Rituximab in renal transplantation. Transplant International. 2013. 563–575.
The A2 subtype does not have circulating antigens linked to von Willebrand factor unlike other antigens, hence less risk of ABMR.
TECHNIQUES OF ABO DESENSITIZATION AND DIFFERENT PROTOCOLS USED OVER TIME
Removal of circulating ABO antibodies
Plasmapheresis-
eliminates approximately 20% of the antibodies by session. removes protective antibodies and coagulation factors.
double filtration plasmapheresis-
Avoids many complications associated with plasma exchange.
Immunoadsorption –
Therasorb column contains polyclonal sheep anti-human IgG antibodies .
Immunosorba columns, that contains staphylococcal protein A bound to sepharose.
immobilized antigens and synthetic epitopes.
These techniques are applied several days before transplantation, their aim is to reduce the circulating anti-A/B antibody levels to achieve titers between 1:8 and 1:32.
Immunomodulation –
administration of high doses of polyclonal intravenous
immunoglobulin (IVIG) to the patient before transplantation.
B cell depletion-
Initially splenectomy used to be done made popular by Japanese transplant program .
Rituximab replaced the need for splenectomy .
Scheme of desensitization treatment
Day -14 = rituximab
Day -10 = MMF
DAY -7 to +7= plasmapharesis/Immunoadsorption f/b IVIG.
Day 0 = tacrolimus + prednisolone
Guy’s Hospital, Barnett et al adopted a tailored desensitization strategy in pairs with ABOi.
titer of < 8= induction and maintenance therapy.
titer of 8 = only RTX
titer between 16 and 64= plasmapheresis was added to RTX
titer > 64 = IA and RTX were used.
With this tailored strategy no difference was observed between ABOi and ABOc groups in allograft and patient survival rates at 1 and 3 years or in the ABMR rates.
CLINICAL OUTCOMES AFTER RENAL TRANSPLANTATION INVOLVING ABOI.
Two systematic reviews and meta-analyses have been published.
review by Lo et al examined 83 studies,4810 kidney transplants involving ABOi were examined.
The main limitation of the review is the lack of randomized controlled trials.
Review showed that patients receiving the newest therapies have a better outcome with fewer severe side effects.
A more recent and wider systematic review gives different results and it examines 7098 renal transplantations involving ABOi.
Transplants involving ABOi compared to those involving ABOc had a significantly higher mortality rates at 1, 3 and 5 years .
Both graft losses and mortality in transplants involving ABOi became equivalent to ABOc transplants at 8 years after transplantation.
This higher mortality could be due to use of high immunosuppression leading to severe viral and bacterial infections and coagulation disorders induced by plasmapheresis and IA leading to bleeding risk.
OPEN CONTROVERSIES IN KIDNEY TRANSPLANTATION INVOLVING ABOI.
Technique of apheresis
Whether to use plasmapheresis which is cheap but leads to removal of all plasma proteins or IA which is 2-3 times costly but specific antibodies can be removed.
Also at what titer aphaeresis is needed is a question.
Role of RTX
As RTX may be removed by plasmapheresis, this technique should be avoided after RTX administration.
In the meta-analysis of ABOi transplants only 35% of patients were treated with RTX.So when and how much to give rituximab is the question.
IVIG
Some authors prefer to divide the IVIG dose 500mg /kg body weight and to administer IVIG in two different sessions 4 d and 1 d before transplantation.
Isoagglutinin quantification
Flow cytometry method is best but costly and not available at all centres.
Tube method
Gel method.
Immunosuppression
Whether steroid withdrawal is feasible is a question.
Post-transplantation apheresis
Whether to be done routinely or only in the case of issagglutinin rebound or high basal levels of antibodies or to be done in case of graft dysfunction .
Accommodation
accommodation is facilitated by the reduction of the isoagglutinin level, by the blockage of complement activation and by RTX. IA- specific columns may facilitate the phenomenon.
Role of protocol biopsies
role on protocol biopsies of C4d in transplantations involving ABOi seems to be related to accommodation when found in
the absence of clinical or other histological abnormalities.
Complications
Haemorrhages are most common in ABOI transplant.
Infections are more common in ABOi transplant.
The incidence of ABMR ranges between 10% and 30% and occurs usually in the first 2 weeks.
KPD
Some points need clarification
Transportation of kidneys vs donor travel
Simultaneous vs no simultaneous exchanges
Closed chains vs open chains
MAKING A CHOICE BETWEEN DESENSITIZATION AND KPD
KPD is generally cheaper with respect to desensitization,but time is needed to find a suitable donor whereas desensitisation is costly but transplant has no delay.
Summary of the Article
Current protocols and outcomes of ABO-incompatible kidney transplantation
The demerit of transplantation from a living donor is that there’s high immunological incompatibility in about 30%.
To overcome the obstacle of incompatibility, different strategies are used:
· Desensitization of the recipient to remove the antibodies and to prevent their rebound after transplantation.
· Kidney Paired Donation(KPD). The exchange of organs between two or more pairs.
Evolution of practice in ABOi-rTX:
· Renal transplantations from A2 donors to O recipients: better results in transplantation involving ABOi are obtained when transplanting kidneys from A2 donors to O recipients. The A2 subtype does not have circulating antigens linked to von Willebrand factor.
· The Japanese strategy was the splenectomy associated with their pretransplantation protocol.
· The strategy of Johns Hopkins University and the Mayo Clinic in the United States; administration of RTX to replace splenectomy.
· Swedish strategy; using antigen-specific immunoadsorption and rituximab for the ABO-incompatible kidney transplantatio.
Desensitization strategies
The frequently used strategies for desensitization are:
1. Removal of circulating antibodies; by plasmapheresis or immune-adsorption.
· Plasma exchange using highly permeable membranes; simple and chief but less effective.The procedure eliminates approximately 20% of the antibodies by session. Additionally, removes protective antibodies and coagulation factors.
· DFPP is performed by two plasma filters, and the second one allows smaller molecules to return back to the patient, avoiding many complications associated with the therapeutic plasma exchange.
· IA; evolution has been made by the use of columns for the selective removal of humoral factors by IA. The advantage of IA is its high capacity to induce ABO agglutinin removal with high biocompatibility and without complement activation.
Types of columns for IA are:
(i) IA with immobilized antibodies: A Therasorb column contains polyclonal sheep anti-human IgG antibodies,which is effective in removal of IgG antibodies. Immunosorba columns, that contains staphylococcal protein A bound to sepharose is effective in removing IgG of different classes.
(ii) IA technique uses immobilized antigens and synthetic epitopes; most specific technique in removing only the undesirable antibodies.
The main steps in the evolution of desensitization:
§ IA or PP2-3 times before Tx plus splenectomy.
§ PP + IVIG + RTX before Tx(no splenectomy).
§ IA and RTX before Tx + LMWH(no splenectomy).
1. Immunomodulation technique : via administration of high doses of polyclonal intravenous immunoglobulin (IVIG) to the patient before transplantation. The aims of IVIG:
• Replacement of IGs that being lost by apheresis techniques.
• It blocks the Fc portion.
• It has immuno-regulatory effect.
2. B cell depletion via splenectomy or RTX.
Clinical outcome after ABOi-rTX
· Transplants involving ABOi compared to those involving ABOc had a significantly higher mortality rates at 1, 3 and 5 years.
· Both graft losses and mortality in transplants involving ABOi became equivalent to ABOc transplants at 8 years after transplantation.
· Coagulation disorders were frequent in transplant involving ABOi.
· Polyoma virus nephropathy was more frequent in patients receiving RTX.
· Many reports document outcomes similar to the standard transplantations leading to controversies and a need to further RCT.
Main controversies in ABOi-rTX:
· Technique of apheresis
· Role of RTX
· IVIG
· Isoagglutinin quantification
· Immunosuppression
· Post-transplantation apheresis
· Accommodation
· Role of protocol biopsies
· Complications
renal transplantation is the optimal management for ESRD, about 30% of patient on the waiting list of transplantation have incompatible donor ( HLA or ABO incompatible )
the solution is the finding of compatible donor deceased or living .
if they have incompatible donor they can wait for compatible one but this option is risky or to do kidney paired exchange or to receive the organ from incompatible donor through de-sensitization.
Immunological aspects
At the renal level,the antigens of the ABO system are expressed on the collecting and distal tubules and on the vascular endothelial cells
Group O individuals have higher antibody titers to both the A and B antigens. As a consequence, recipients of blood type O have a higher incidence of antibody-mediated rejection (ABMR) after transplantation
Better results in transplantation involving ABOi are obtained when transplanting kidneys from A2 donors to O recipients. The A2 subtype does not have circulating antigens linked to von Willebrand factor.
The reaction of isoagglutinins with the antigens of the ABO group induces complement activation, as documented by the presence of C4d
Techniques of ABO desensitization and different protocols used over time
Removal of circulating antibodies
it is done several days before transplantation, to reduce the circulating anti-A/B antibody levels to achieve titers between 1:8 and 1:32
Immunomodulation
by administration of high doses of polyclonal intravenous immunoglobulin (IVIG) to the patient before transplantation, to replace the patient’s immunoglobulins lost because of apheresis techniques.
B cell depletion B
B cells produce isoagglutinins, and their reduction is essential to obtain effective desensitization. Historically, splenectomy has been used for B cell depletion. To date, RTX, a humanized monoclonal antibody that binds to CD20 expressed on the B cell membrane, is the drug used to obtain B cell depletion. the aim of B cell depletion is to reduce the agglutinin titer to a predetermined level.
Clinical outcomes after renal transplantation involving ABOI
By 2007, Genberg et al.,showed that there was no significant difference in patient and graft survival or in the rejection episode rates.at 3 years follow up between patients with ABO compatible renal transplantation and Incompatible recipients who were treated with IA and a single dose of RTX (375 mg/m2 of body surface) 30 d before transplantation and IVIG at a dose of 0.5/kg body weight in the day before transplantation.
A more recent and wider systematic review gives different results . This review examines 7098 renal transplantations involving ABOi.Overall, transplants involving ABOi compared to those involving ABOc had a significantly higher mortality rates at 1, 3 and 5 years . Both graft losses and mortality in transplants involving ABOi became equivalent to ABOc transplants at 8 years after transplantation.The higher mortality rate is probably a consequence of the high immunosuppression related to the therapy.
Immunosuppression
Apart from desensitization, the immunosuppression in kidney transplantation with ABOi is similar to that used for standard transplantation. The basal immunosuppression begins together with the desensitization. The possibility of steroid withdrawal is discussed. Some studies have documented a high risk of ABMR in the case of steroid withdrawal soon after transplantation. Other studies have documented a high risk for acute rejection even in the case of late withdrawal.
Accommodation
In the presence of circulating antibodies and antigens on the graft cell surface, the graft itself may not be rejected.
The pathogenesis of the accommodation seems to be due to the presence of a low titer of antibodies, with low affinity and with the blockage of complement activation . Under these conditions, endothelial cells develop a phenotypic change according to which they become resistant to antibody damage.
the presence and the role on protocol biopsies of C4d in transplantations involving ABOi seems to be related to accommodation when found in the absence of clinical or other histological abnormalities.
Complications
Kidney paired donation (KPD)
The hypothesis of overcoming the immunological barriers in a different way without the desensitization of the recipient was first proposed by Rapaport in 1986. The simplest model of the KPD is the two-way.
Indeed, given the fact that KPD is generally cheaper with respect to desensitization.
Introduction
Renal transplantation is considered the best therapy for patients affected by end-stage renal disease. or such patients, to avoid a long time on dialysis, transplantation from living donor is the best option. However, approximately 30% of such transplantations are considered incompatible from the immunological point of view either because of the presence in the recipient of antibodies directed against the human leukocyte antigen (HLA) antigens of the donor or because of the incompatibility of the ABO system between the donor and recipient or because of
both.
There are two principal strategies to overcome these barriers: To desensitize the recipient to remove the antibodies and modify the immunological status, allowing the transplant; and To exchange the organs between two or more pairs to exchange the organs between different donors.
TECHNIQUES OF ABO DESENSITIZATION AND DIFFERENT PROTOCOLS
USED OVER TIME
A) Removal of circulating ABO antibodies
The removal of circulating ABO antibodies is obtained principally by plasmapheresis or immune-adsorption (IA). The aim of these strategies, principally applied several days before transplantation, is to reduce the circulating anti-A/B antibody levels to achieve titers between 1:8 and 1:32.
B) Immunomodulation
his technique consists in the administration of high doses of polyclonal intravenous
immunoglobulin (IVIG) to the patient before transplantation. The aim is to replace thepatient’s immunoglobulins lost because of apheresis techniques. In addition, IVIG blocks the Fc receptor and has immunoregulatory properties.
C) B cell depletion
B cells produce isoagglutinins, and their reduction is essential to obtain effective desensitization.
In the past, it was done by spenectomy but we use anti-CD20 (rituximab)
Initially, the most frequently used technique was the removal of circulating anti-ABO
antibodies by plasmapheresis. The technique is effective but has the disadvantages of removing blood components that are useful to the patient and causing coagulation disorders. More recently, principally in Europe, plasmapheresis has been replaced by the technique of the IA of isoagglutinins using specific protein A or anti-human Ig columns. The main advantages of this technique are to its high capacity to induce ABO agglutinin removal with high biocompatibility and without complement activation.
Since then, almost all desensitization strategies used the administration of IVIG to improve immunomodulation and the administration of RTX to avoid splenectomy.
More recently, at the Guy’s Hospital, Barnett et al adopted a tailored desensitization strategy in pairs with ABOi. The different strategies were adopted according to the initial anti-ABO antibody titer. With a titer of 8, only RTX was used; with a titer between 16 and 64, plasmapheresis was added to RTX therapy; and with a titer > 64, IA and RTX were used. In total, 62 kidney transplants involving ABOi were performed using this strategy, and the results were compared with 167 ABOc transplants. No difference was observed between the two groups in allograft and patient survival rates at 1 and 3 years or in the ABMR rates.
These results highlight that a tailored desensitization strategy obtains good results with personalized therapy and lower costs.
Renal transplantation as the best choice for ESRD is faced with difficulties in finding full matched donors. this is solved either by desensitisation or paired donation. In this review, the current protocols of desensitization are summarized. since the introduction of ABO incompatible transplant recently, rituximab replaced splenectomy, as well as advancements in plasmapheresis techniques.
Recipients with blood group O have the most chance of AMR because of the chance of having antibodies to both A and B blood groups.
blood group A2, on the contrary, have the lowest risk. They do not have circulating antibodies linked to VWF.
ABO antigens reaction with isoagglutinin seems to activate complement as shown by c4d deposition.
With the improvement of AMBR treatment protocols and techniques of desensitization in addition to rituximab, the ABOi tx dramatically increased in the last decades.
Techniques of ABO desensitization used over time can be summarized as techniques for the removal of circulating ABO antibodies, immunomodulation and B cell depletion.
Removal of circulating ABO antibodies:
principally by plasmapheresis or immune-adsorption. The aim is to lower the ab titers to less than 1:32 (1.8-1:32) several days before transplantation. plasmapheresis removes nearly 20% in each session. double filtration is done to lower complications associated with standard plasmapheresis by allowing smaller molecules to return to the patients. Immune-adsorption allows selective removal of certain antibodies. here are two types of IA columns: sheep or those containing staphylococcal protein A.
Immunomodulation:
By giving polyclonal IVIG, we replace the patients’ immunoglobulin. IVIG also blocks the Fc receptor and also has immunoregulatory properties.
B cell depletion
B cells produce isoagglutinin. For this reason, it is very important to reduce them for effective desensitization.
Historically splenectomy was used. After the introduction of anti-CD20, Rituximab replaced splenectomy.
….
When exposed to a low titer of ABO antibody, the transplanted kidney develops a capacity to resist complement activation. This long-lasting phenomenon is known as ACCOMMODATION.
Different techniques and protocols developed over time. Immuadsorption has fewer side effects, especially regarding hypercoagulability seen after plasmapheresis. some centres used only rituximab for low titers of antibodies.
ABOi kidney transplantation and KPD are the ways used to the overcome shortage of deceased donor organs and to allow patients to avoid long waiting time on dialysis.
ABO system antigens are expressed on RBCs, tubules and vascular endothelium.
ABOi was a contraindication for kidney transplantation.
However, ABOi transplants increased worldwide due to improvement in diagnosis and treatment of AMR.
The outcomes of ABOi transplants were similar to those with standard risk.
Techniques of ABO desensitization and different protocols used:
Removal of circulating ABO antibodies:
Plasmapheresis removes 20% of antibodies per session .
Double filtration PP is safer than PTx.
High dose of IVIG used to replace immunoglobulins lost with apheresis techniques in addition to its immunoregulatory effects to decrease antibody rebound and risk of AMR.
Now rituximab replaced splenectomy to obtain B cell depletion to decrease agglutinin titer to predetermined level.
A systemic review examined 83 studies highlighted the efficacy of rituximab and IA but was limited by absence of randomized controlled trials.
A wider systemic review showed that ABOi transplants have significantly higher mortality rates than ABOc transplants at 1,3 and 5 years, mostly due to intense immunosuppression causing severe infections.
Role of rituximab is not well determined and seems to be unnecessary in some patients.
The effect of steroid withdrawal either early or low is not well studied.
Accommodation is lack of rejection in presence of circulating ABO antibodies with normal kidney function and normal histology.
It is facilitated by reduction of isoagglutinin levels, blocking of complement activation and rituximab.
Current protocols and outcomes used in ABO incompatible renal transplantation
Living donor incompatible renal transplants are now possible after HLA desensitization or ABO antibody removal technique. by performing ABO incompatible renal transplants we can increase the donor pool and reduced the waiting time of the patients on dialysis….
ABO incompatible renal transplantation came into picture after the year 2000…Initially Japan used to perform a lot of ABO incompatible renal transplants due to a poor deceased donor program in the beginning…Their protocols used splenectomy initially before 2002 due to regulatory use of rituximab by their own National health service…After 2002, japan has used rituximab in ABOi renal transplants and their results re extensively published. Later, Mayo and the European (Stockholm and Belgium) published their experience on ABO incomaptible renal transplantation using IA techniques and IVIG…
Antibody removal technique can be divided into the following
Antibody removal techniques:
This is done using Plasmaphresis and IA technique.. Plasmaphresis involves removing the plasma volume and replacing the volume with FFP of the AB type blood group..It has the disadvantage of normal coagulation factors and non specific immunoglobulin removal too…Although cheaper than IA, it is associated with infections and coagulation parameters….The DFPP using another plasma filter after removal that allows the return of the normal immunoglobulins and makes it more selective…Immunoadsorption techniques removes the antibody based on adsoprtion principle. Various adsorption columns are available…IA using staphylococcal protein A and aother coloumn using polyclonal sheep antibody are available….
IVIG:
This is given just before the time of surgery in some transplant protocols to replenish the Ig lost during the apheresis sessions and act as an immunomodulator after transplants….
B cell depletion technique:
It started with splenectomy in the 2000’s but later it was replaced by rituximab in many centers…Rituximab has been used in most of the modern day protocols with standard 2 doses of 375mg/m2 given minus 2 weeks post transplant. Various studies have evaluated Inj rituximab 200mg IV as a part of ABO densensitization protocol…
Many centers use a tailored imunosuppression protocols for ABO desensitization….
Issogluttin titre <1:8 – direct transplant
1:8 – Rituximab 1 dose
16-64 – Rituximab + DFPP
>64 – Rituximab + IA
The overall mortality and patient outcome as per various studies are comparable to ABOi vs ABOc renal transplants till a metanalysis published in the LANCET 2019….After this robust metanalysis which compared nearly 40 studies across various continents proved that ABOi renal transplants have a higher mortality as compared to ABOc renal transplants at 1,3,5 years… more than 8 years there was no difference in the outcome between ABOi and ABOc renal transplants….
Current protocols and outcomes of ABO-incompatible kidney transplantation
Living donor ABO incompatible kidney transplantation has become safe and effective due to the advancement of recipient desensitisation protocol and kidney paired donation. Desensitisation protocol include antibody reduction by plasmapheresis or immune-adsorption (IA); Inhibition of antibody production by splenectomy which has been replace by Rituximab recently; Pleiotropic action of IVIG; and Complement inhibition by eculizumab.
Plasmapheresis or immune-adsorption (IA) involve removal of circulating ABO antibodies in the recipients before transplantation. The antibody titers between 1:8 and 1:32 is desirable . Double filtration plasmapheresis allow returning of protective antibodies and coagulation factors this lowering the risks associated with therapeutic plasma exchange. On the other hand, the most specific IA technique that applying the immobilised antigens and synthetic epitopes to remove only the undesirable antibodies.
Immunomodulation by using high dose of polyclonal IV IG replace the immunoglobulins loss during apheresis. IV IG block the Fc receptor on the leukocyte membrane; Inhibit the complement activation and circulating antibodies towards HLA.
For effective B cell depletion IV Rituximab has been replaced splenectomy in most desensitising protocol. However, post-transplant plasmapheresis should be avoided if IV Rituximab is used at desensitisation protocol. This is because plasmapheresis can reduce Rituximab efficacy by removing it from circulation.
Accommodation is defined as presence of circulating isoagglutinins and antigens on the graft cells with normal renal function and positive C4d on the peritubular capillaries. Eculizumab, a monoclonal antibody against C5, may facilitate accommodation and serve as rescue therapy in the case of severe antibody medicated rejection ( ABMR ).
The complications of ABO incompatible renal transplant include are the same as ABO compatible renal transplant except risk of bleeding is generally higher in ABO incompatible group who received apheresis treatments. Infection risk is dependent on intensity of desensitisation strategy. The incidence of ABMR ranges between 10% and 30% especially in the first 2 weeks following transplantation.
The controversies in ABO incompatible renal transplant include apheresis technique used, role of rituximab, utility and role of IVIG, method to detect isoagglutinins quantity, type of immunosuppression and post transplantation apheresis, accommodation, role of protocol biopsies and complications.
Kidney pair donation ( KPD ) program ( K may overcome the immunological barrier of kidney transplantation. There are some issues pertaining to KPD such as transportation of kidneys and donor travel, simultaneous versus no simultaneous exchanges and whether the transplant process is a closed chains or open chains.
In my opinion, we need to personalise the desensitising protocol and immunosuppressive regimen for ABO incompatible kidney transplantation. However, we need to bear in mind that ABO incompatible generally more costly as compare ABO compatible renal transplant. Risks ABO incompatible transplant should be explained to potential recipients. KPD may serve as alternative to over come the immunological barrier.
ABO incompatibility is approximately 30% of the immunological barrier for solid organ transplantation because of the presence in the recipient of antibodies directed against the human leukocyte antigen system of the donor. Two different strategies are used to overcome these barriers: desensitization of the recipient to remove the antibodies and the exchange of organs between two or more pairs. There is no overall agreement on desensitization protocols, types, and doses of immunosuppressive medications. There are no large RCT studies to be sure of the optimum management. The target is to get successful transplantation with the least complications and use the least amount of immunosuppressive medications to decrease complications and cost.
The major 4 cornerstones in ABOi transplantation include (in order to reach anti-A/B antibody titers between 1:8 and 1:32)
· removal of antibodies using plasmapheresis, IA, DFPP
o plasma exchange: is a simpler, cheaper, but less effective technique that has been the using highly permeable membranes. The procedure eliminates approximately 20% of the antibodies
o The double filtration plasmapheresis: is performed by two plasma filters, and the second one allows smaller molecules to return back to the patient, avoiding many complications associated with the therapeutic plasma exchange
o IA: There are different types of columns for IA.
§ IA with immobilized antibodies: are the most widely used in which column contains polyclonal sheep anti-human IgG antibodies and is effective in removing IgG antibodies. A different IA technique uses immobilized staphylococcal protein A. These Immunosorba columns, that contain staphylococcal protein A bound to sepharose is effective in removing IgG of different classes. Additionally, are able to induce a B cell apoptosis, so enhancing the immunosuppressive effect.
§ IA technique uses immobilized antigens and synthetic epitopes and is the most specific technique in removing only the undesirable antibodies
· Immunomodulation using IVIG: blocks the Fc receptor and has immunoregulatory properties
· blockage of complement system using eculizumab
· depleting of b-cell using splenectomy or rituximab
there is what is called an on-demand strategy in which the whole desensitization protocol is based according to the initial titer of anti-ABO antibodies in an attempt to reduce the costs
for example, at the Guy’s Hospital, Barnett et al adopted a tailored desensitization strategy in pairs with ABOi according to the initial anti-ABO antibody titer. With a titer of 8, only RTX was used; with a titer between 16 and 64, plasmapheresis was added to RTX therapy; and with a titer > 64, IA and RTX were used. No difference was observed regarding allograft and patient survival rates at 1 and 3 years or in the ABMR rates. These results highlight that a tailored desensitization strategy obtains good results with personalized therapy and lower costs.
Outcomes of ABOi kidney transplantation
Results need to be confirmed by large RCT but according to 2 meta-analyses of observational studies
· Both graft losses and mortality in transplants involving ABOi became equivalent to ABOc transplants at 8 years after transplantation
· transplants involving ABOi compared to those involving ABOc had a significantly higher mortality rate at 1, 3, and 5 years
· Coagulation disorders were also frequent in transplants involving ABOi. This complication is probably related to the modifications in the coagulation system induced by plasmapheresis or IA
· infectious disease specially Polyomavirus nephropathy was also more frequent in patients receiving RTX, as documented by several authors.
· Surgical complications in transplantations involving ABOi are similar to complications of standard transplants, with the exception of hemorrhages.
· ABMR is the first cause of graft loss in transplantations involving ABOi, However, it should be highlighted that both the antibody basal titer before desensitization and the post-transplantation titer has a low predictive value for ABMR
· ABOi transplants are more expensive than the ABOc transplants, however, they are less expensive than dialysis. in the case of ABOi transplant $ 65080 per transplant episode vs $32039 per transplant episode for an ABOc transplant.
CONCLUSION
the ABOi renal transplantation. Outcomes are almost similar to standard transplantations. The immunological barriers represented by the different ABO groups have been overcome and no major agreement on doses, types of immunosuppressive medications, and several questions still need to be answered like
· Apheresis technique used
· Role of rituximab
· Utility and role of IVIG
· Method to detect isoagglutinin’s quantity
· Type of immunosuppression
· Utility of post-transplantation apheresis
· Accommodation
· Role of protocol biopsies
· Principal complications
ABO incompatibility is approximately 30% of the immunological barrier for solid organ transplantation .
Two different strategies are used to overcome these barriers:
* desensitization of the recipient .
*Paired Kidney Donation
Different protocols used for desensitization for ABO :
A-Removal of circulating antibodies :
1- plasmapheresis :
Plasmapheresis :
Advantage : simple , cheaper
Disadvantages :
non-selectivity of removal of all immunoglobulins thus risk of infection is increased
hypocalcemia
coagulation factors deficiency.
20% of antibodies are removed within 1 session
The double filtration plasmapheresis: done by two plasma filters, and the second one allows smaller molecules to return back to the patient, avoiding many complications associated with the therapeutic plasma exchange.
2- Immunoadsorption :
Types of columns for IA.
IA with immobilized antibodies: .
IA with immobilized antigens and synthetic epitopes and is the most specific technique in removing only the undesirable antibodies
B- Immunomodulation:
by using IVIG to
replace immunoglobulin lost during plasmapheresis
block FC receptors
complement inhibition
inhibit B/T-cell proliferation
increase B cells apoptosis
suppression of CD8 T-cell cytotoxicity.
C-B cell depletion :
Splenectomy:
replaced by using Rituximab ( medical spleenectomy)
Rituximab:
as it leads to depletion of B cells by binding to CD20 on these cells.
side effects: fever, chill, headache, and nausea
dose: 375mg/m2 1 month before KT
Different protocols used for desensitization :
in Europe :
IA is used more frequently and dose of Rituximab added 1 month before KT and one dose of IVIG 0.5 gm/kg one day before ABOi-KT
More recently, at the Guy’s Hospital :
ABO titer of 8 : only Rituximab was used
and of titer 16and 64: Rituximab + PP were used
and titer > 64: Rituximab + IAs were used
Accommodation :
is defined as presence of antibodies but no harm and explained by change in the structure of antigens , specificity of the antibodies.
Clinical Outcomes in ABOI-KT :
Higher mortality rates in ABOi-KT more than in ABOc-KT at 1, 3, and 5 years
with no difference in mortality rates at 8 years
Complications:
-surgical complications nearly same as ABOc-KT but increased risk of hemorrhage due to loss of coagulation factors during PP
Infections: increase risk of infections of BK, CMV, HSV
ABMR increases the risk of ABMR in ABOi-KT
Desensitization V.S KPD:
KPD is preferred on ABOi KT due to its low cost, no need for desensitization, and low immunological risk.
This article reviews different protocols and outcome of ABOi-KT as a solution for organ shortage and remaining on dialysis for a long time.
Immunological aspects: ABO antigens are glycoproteins express on RBC, endothelial and epithelial cells.
Recipients of blood group O, have high Ab titers to A and B antigens. So, they have higher risk of ABMR after TX. In addition to membrane-bind Ags, circulating antigens linked to Von willebrand factor exist in some patients and cause complement activation and C4d deposits. The persons with A2 subtype does not have circulating Ags.
Different desensitization protocols used over time:
1. Removal of circulating ABO antibodies:
This removal performed by DFPP or IA several days before TX to reduce anti-A/B Ab level to a level between 1:8 and 1:32.
DFPP is used by two filters and the second one permits return of vital molecules to the patient to decrease complications.
IA used different columns to remove selectively some humoral factors.
IA with a therasob column is effective in removing IgG Abs (by polyclonal sheep anti-human IgG Abs.
Immunosorba columns are effective in removing different classes of IgG and induce B cell apoptosis. Another one uses synthetic epitopes in addition to immobilized Ags and is the most specific technique.
2. Immunomodulation:
High doses of polyclonal IVIG is administered to the patient before TX to replace immunoglobulins lost and block the FC receptor.
3. B cell depletion:
To reduce production of isoagglutinin. This is done by splenectomy in the past and by using rituximab in recent years,
After 2 weeks, the transplanted kidney develops accommodation which means lack of rejection in spite of presence of ABO Abs.
Different protocols were evolved over time, by substitution of splenectomy by using rituximab and using different doses of rituximab, IVIG or IA according to patients isoagglutinin titers.
Clinical outcomes after ABOi-KT:
The results of studies with a low number of patients are generally good.
* There are two systematic review in this context.
The first one by ho et al, examined overall 4810 ABOi-KTs and showed that RTX and IA could have a superior efficacy but there were no RCTs comparing different protocols.
The second one was performed among 7098 ABOi-KTs.
Comparing with ABOC-KT, ABOi-KTs had higher mortality rates at 1,3 and 5 years. But graft losses and mortality in ABOi-KT became equivalent to ABOc-KT at 8 years post-TX. This was probably related to the side effect of high immunosuppression and severe bacterial or viral infections, showing need for reducing immunosuppression or desensitization therapy.
There are controversies in ABOi-KT:
1. Technique of apheresis:
Specific columns for IA are effective with fewer side effects but higher costs to reach a titer of 1:8 before TX.
What to do with patients with a low titer isoagglutinin?
2. Role of rituximab:
Although RTX replaced splenectomy, is it necessary in all patients? In recent meta-analysis only 35% of patients received RTX.
3. IVIG:
IVIG is used usually 500 mg/kg on the day before TX. But there are still different protocols.
4. Isoagglutinin quantification:
The best method is flux cytometry with high cost but tube and gel techniques are used, too.
5. Immunosuppression:
This is usually the same far standard TX. There are controversies about steroid – withdrawal.
6. Post TX apheresis:
Some authors do it in patients with isoagglutinin rebound.
7. Accommodation:
Low titer Abs, with low affinity and blockage of complement activation. Eculizumab, may facilitate accommodation or rescue therapy.
8. Protocol biopsies:
They usually show C4d in PTC with no sign of ABMR related to accommodation.
9. Complications:
Hemorrhages were associated with the number of IA. Infections complications related to immunosuppression and desensitization protocols were seen.
The incidence of ABMR was between 10%-30%.
KPD: KPD is a different way to overcome organ shortage. There are several models with growing suggestions for different models of single-center, regional, national or international strategies.
The major hurdle in transplantation from living donor is that approximately 30% are immunologically incompatible because of the presence in the recipient of antibodies directed against the human leukocyte antigen system of the donor or because of the incompatibility of the ABO system.
This review article has tried to describe the different protocols to proceed with ABOi kidney transplant and it’s clinical outcome as well.
There are two principal strategies to overcome these barriers:
(1) To desensitize the recipient to remove the antibodies and modify the immunological status, allowing the transplant; and
(2) To exchange the organs between two or more pairs to exchange the organs between different donors.
Removal of circulating ABO antibodies
The removal of circulating ABO antibodies is obtained principally by plasmapheresis or immune-adsorption (IA). The aim of these strategies, principally applied several days before transplantation, is to reduce the circulating anti-A/B antibody levels to achieve titers between 1:8 and 1:32.
Immunomodulation
This technique consists in the administration of high doses of polyclonal intravenous immunoglobulin (IVIG) to the patient before transplantation. The aim is to replace the
patient’s immunoglobulins lost because of apheresis techniques. In addition, IVIG
blocks the Fc receptor and has immunoregulatory properties.
B cell depletion
B cells produce isoagglutinins, and their reduction is essential to obtain effective desensitization.
Intially splenectomy was considered a vital step for B cell depletion but now medical splenectomy with Rituximab has taken over as standard of care in different protocols of desensitization.
Guys hospital has adopted a tailored desensitization strategy in pairs with ABOi.
According to isoagglutinin titers Rituximab plus PP or IA was used . IA was added only for titer of 1:64 or above.
CLINICAL OUTCOMES AFTER RENAL TRANSPLANTATION INVOLVING
ABOI
In recent years, two systematic reviews and meta-analyses have been published and shed more light on the clinical outcomes of kidney transplantation involving ABOi.
Overall, transplants involving ABOi compared to those involving ABOc had a significantly higher mortality rates at 1, 3 and 5 years (odds ratio 2.17, 1.89 and 1.47, respectively; P < 0.0001).
Both graft losses and mortality in transplants involving ABOi became equivalent to ABOc transplants at 8 years after transplantation.
Coagulation disorders, Polyoma virus infection and severe bacterial or virus infection due to excessive immunosupression could be reason of increased mortality noted.
Major controversies encountered in ABOi renal transplant are
Apheresis techniques used
Role of Rituximab
Utility and role of IVIG
Method to detect isoagglutinin titers
Type of immunosupression
Utility of post transplant Apheresis
Concept of Accommodation and it’s exact role
Role of protocol biopsies
Principal complications
KPD
This could be one way of crossing immunological barrier however there are several points that needed clarification.KPD is cheaper but it’s availability in short time is big question
Current protocols and outcomes of ABO-incompatible kidney transplantation.
Approximately 30% of such transplantations are considered incompatible because of
HLA antigens of the donor or incompatibility of the ABO system between the donors and
recipient.
Two methods to overcome these barriers:
(1) To desensitize the recipient to remove the antibodies and modify the immunological
status.
(2) To exchange the organs between two or more pairs PKD.
Worldwide increase in the rate of kidney transplantations from living donors that involved
ABOi. This fact may be principally ascribed to four factors.
(1) knowledge of the diagnosis and treatment of ABMR has substantially improved.
(2) Japanese authors published excellent results in renal transplantations involving ABOi.
(3) Later, Johns Hopkins University and the Mayo Clinic in the United States documented
the possibility of performing such transplantation without splenectomy with the
administration of an anti-CD20 monoclonal antibody rituximab.
(4) Finally, Swedish authors developed a new technique that demonstrated outcomes in
renal transplantation involving ABOi that were similar to the outcomes of standard renal
transplantation.
TEHNIQUES OF ABO DESENSITIZATION AND DIFFERENT PROTOCOLS USED
OVERTIME
Removal of circulating ABO antibodies:
Plasmapheresis or immune-adsorption (IA).
The aim of these strategies:
Principally applied several days before transplantation, is to reduce the circulating anti-
A/B antibody levels to achieve titers between 1:8 and 1:32
The apheretic techniques:
The simpler, cheaper, but less effective technique has been the therapeutic plasma
exchange using highly permeable membranes.
The procedure eliminates approximately 20% of the antibodies by session. Additionally,
removes protective antibodies and coagulation factors.
The double filtration plasmapheresis is performed by two plasma filters, and the
second one allows smaller molecules to return back to the patient, avoiding many
complications associated with the therapeutic plasma exchange.
Types of columns for IA.
IA with immobilized antibodies: are the most widely used. A Therasorb column
contains polyclonal sheep anti-human IgG antibodies and is effective in removing IgG
antibodies.
Immobilized staphylococcal protein A.
These Immunosorbent columns, that contains staphylococcal protein A bound to
sepharose is effective in removing IgG of different classes. Additionally, are able to
induce a B cell apoptosis, so enhancing the immunosuppressive effect.
Another IA technique uses immobilized antigens and synthetic epitopes and is the
most specific technique in removing only the undesirable antibodies.
Immunomodulation:
Administration of high doses of polyclonal IVIG to the patient before transplantation.
Immunoglobulins lost because of apheresis techniques.
In addition, IVIG blocks the Fc receptor and has immunoregulatory properties.
B cell depletion:
Historically, splenectomy has been used principally in Japan for B cell depletion.
To date, RTX, a humanized monoclonal antibody that binds to CD20 expressed on the B
cell membrane, is the drug used to obtain B cell depletion.
Literature different protocols:
Initially plasmapheresis.
Technique of the IA, recently principally in Europe, plasmapheresis has been replaced
by the technique of the IA of isoagglutinins using specific protein A or anti-human Ig
columns.
Most all desensitization strategies used the administration of IVIG to improve
immunomodulation and the administration of RTX to avoid splenectomy.
More recently, at the Guy’s Hospital, Barnett etal adopted a tailored desensitization
strategy in pairs with ABOi. The different strategies were adopted according to the initial
anti-ABO antibody titer with a titer of 8, only RTX was used;
With a titer between 16 and 64, plasmapheresis was added to RTX therapy;
And with a titer > 64, IA and RTX were used.
CLINICAL OUTCOMES AFTER RENAL TRANSPLANTATION INVOLVING ABO:
Overall, transplants involving ABOi compared to those involving ABOc had a significantly
higher mortality rates at 1, 3 and 5 years.
Both graft losses and mortality in transplants involving ABOi became equivalent to ABOc
transplants at 8 years after transplantation.
Excess immunosuppression is the cause of severe bacterial or viral infections.
Coagulation disorders were also frequent.
OPEN CONTROVERSIES IN KIDNEY TRANSPLANTATION INVOLVING ABO:
Main controversies .
Apheresis technique.
Used Role of rituximab .
Utility and role of IVIG .
Method to detect isoagglutinins .
Quantity Type of immunosuppression.
Utility of post transplantation apheresis.
Accommodation Role of protocol biopsies.
Principal complications.
KPD:
The simplest model of the KPD is the two-way, in which two pairs of donors and
recipients with ABOi exchange the kidneys, thereby resolving the incompatibility.
The model may also include a higher numbers of pairs realizing the KPD at three-way,
four-way, and so on.
A further increase in kidney exchanges was realized by the domino KPD, which start
from an altruistic donor and finish with the donation of a kidney to a recipient on the
waiting list.
A variant of domino KPD is the Never Ending Altruistic chain, which allows a higher
number of recipients to be transplanted by the use of bridge donors.
CONCLUSION:
To date, the ABOi renal transplantation is possible because of the reconditioning
strategies available. Many reports document outcomes similar to the standard
transplantations.
ABOi transplants are more expensive than the ABOc transplants, however they are less
expensive than dialysis.
Renal transplantation is considered the treatment modality of choice for ESKD patients.
Nevertheless, HLA and ABO incompatibility challenge undermine this process. Strategies to overcome the incompatibility barriers continued to develop. As this incompatibility, considered the main risk factor for development of AMR which portend the risk of premature loss of the allograft.
Strategies for desensitization developed over time to overcome this risk, include:
1] Removal of ABO antibodies:
a- Aiming at lowering the antibody titer to less than 1/32 at the time of transplantation.
b-Performed pre-transplantation to optimize immunologic tolerance and minimize hyperacute rejection risk.
c-Include PP where in highly permeable plasma filter, used to remove the antibodies ,with drawback of removing the protective antibodies and coagulation factors, carrying a higher risk of bleeding.
d-DFPP, uses two plasma filters ,permitting the return of smaller molecules to the patients, reducing the risk of bleeding.
e-IA : is the latest technology used for the clearance of circulating antibodies. Its the most specific procedure to remove the undesired antibodies.
f-IA main draw back is highly expensive procedure.
g- The post operative removal of antibodies is not routinely performed, but it depends on antibody rebound reflected as post transplant antibody titer on-demand strategy. Rebound will be critical only for the first 2 weeks post transplant after which the risk of rejection is minimal even with rebound and activation of complement system, a phenomena called accommodation.
2] Immunomodulation:
High dose of polyclonal immunoglobulins [IVIG] is administered preoperatively to replenish the immunoglobulines lost by PP. Its blocking the FC receptors in different cell types. Furthermore it has several modulatory functions as well.
3] B-lymphocyte depletion.
As the B-lymphocytes are the source of isoagglutinins, it was mandatory to be depleted in order to precondition the patient with desensitization for ABOi transplantation.
Historically splenectomy was the modality of choice. Replaced efficiently by Rituximab {RTX}.
Protocols for desensitization:
1] PP, DFPP and IA, IVIG and RTX:
RTX 30 days prior to Transplantation 375 mg/mm, IA until Isagglutinin titer less than 32%, and IVIG 0.5 g/kg one day before transplantation.
2] Due to high risk of post transplant infectious complication, different protocol adopted to minimize immunosuppression. like considering IA and IVIG only protocol.
3} In Guys hospital , depending on Antibody titer, strategy was set as follow:
a-Titer less than 8%, only one dose of RTX.
b-16-64 % PP and RTX
c-more than 64% IA and RTX.
Evaluating outcomes after transplantation:
2 large scale meta analysis were, conducted to evaluate the outcome of ABOi renal transplantation, showed different results, with good outcome in the first in Lo et al study and poor out come with Florin G scurt et al
The vast majorities of controversies revolve around the desensitization strategy .
Main debates encountered :
apheresis techniques
RTX
IVIG
Post Transplant pheresis.
Detection of isoagglutinin titer.
accommodation.
protocol biopsy
type of immunosuppression.
PKD:
Offer safer and more feasible strategy to overcome the ABOi barrier. In USA PKD is growing and desensitization strategy is dropping.
Renal transplantation is the best therapy for ESRD patients
living kidey donor is the best option but many of recipients on the waiting list are sensitized and its difficult to find matched doner for them.
Also waiting for deceased donor might be for many years due to shortage of organs
two principal strategies to overcome these barriers: (1) desensitize to remove the antibodies (2) Paired kidney exchange programmes.
ABOI-KT helped to increase donor pool.
▪︎IMMUNOLOGICAL ASPECTS
ABO system antigens are expressed on RBCs, epithelial ,endothelial cells,collecting and distal tubules and on the vascular endothelial cells.
Bl.group A has anti B antibodies, while Bl.group B has anti A antigens antibodies
O individuals have higher antibody titers to both the A and B antigens
So they remain for longer time on waiting list and have a higher incidence of ABMR.
There are also circulating epitopes A and B, both are soluble and linked to von Willebrand factor exist in some patients,These antigens, when free, are responsible for ABMR.
better results in transplantation involving ABOi are obtained when transplanting kidneys from A2 donors to O recipients.
The A2 subtype does not have circulating antigens linked to von Willebrand factor.
▪︎ DESENSITIZATION AND DIFFERENT PROTOCOLS USED OVER TIME
Combination of different strategies are applied
*Removal of circulating ABO antibodies
The aim is reduction of isoagglutinin levels to achieve titers between 1:8 and 1:32.
•plasmapheresis; simple and cheape,and less effective it removes 20% of the antibodies by session also removes protective antibodies and coagulation factors.
•The double filtration plasmapheresis avoids many complications associated of plasma exchange.
The number of apheresis session is variable till reaching a titer of 1:8 before transplantation.
•Immune-adsorption
IA with immobilized antibodies: are the most widely used
It’s effective in removing IgG of different classes and induces B cell apoptosis, so enhancing the immunosuppressive effect.
Another IA technique uses immobilized antigens and synthetic epitopes and is the most specific technique in removing only the undesirable antibodies.
•Intravenous immunoglobulin (IVIG) given to
patient before transplantation after plasmapheresis ,IVIG blocks the Fc receptor and has immunoregulatory properties.
It is givin in a dose 500 mg IVIG/kg body weight 1 day before transplantation or divided on 4 d and 1 d before transplantation.
•B cell depletion
B cells produce isoagglutinins, and their reduction is essential to obtain effective desensitization.
Historically, splenectomy has been used replaced now by anti CD20 monoclonal antibody rituximab .
RTX reduces the risk of isoagglutin rebound, the risk of ABMR and the risk of chronic rejection.
•Accommodation:a phenomenon that occurs in the first 2 weeks post transplantation due to exposure to low ABO antibody titer allows the graft to resist complement-mediated damage.
•Different protocols for desensitization
in Europe, plasmapheresis was replaced by the technique of the IA of isoagglutinins using specific protein A or anti-human Ig columns due to its high capacity to induce ABO agglutinin removal with high biocompatibility and without complement activation.
all desensitization strategies used the administration of IVIG +Rituximab.
By 2007, Genberg et al compared with 27 transplants between ABO compatible (ABOc) pairs. Incompatible recipients were treated with IA and a single dose of RTX (375 mg/m2 of body surface) 30 d before transplantation. The day before transplantation, the patients were given IVIG at a dose of 0.5/kg body weight.
There was no significant difference in patient and graft survival rates or in the rejection episode rates. The patient follow-up was as long as 3 years, and at 3 years, the same estimated glomerular filtration rate was observed in both groups.
Later they observed a harmful antibody rebound after the interruption of IA and suggested that patients should be carefully monitored both before and after transplantation.
More recently, at the Guy’s Hospital, tailored desensitization strategy in pairs with ABOi. According to initial anti-ABO antibody titer so With a titer of 8, only RTX was used; with a titer between 16 and 64, plasmapheresis was added to RTX therapy; and with a titer > 64, IA and RTX were used.
using this strategy, the results were compared with ABOc transplants. No difference in allograft and patient survival rates at 1 and 3 years or in the ABMR rates.
•Immunosuppression
immunosuppression in ABOi-KT is similar to that used for standard transplantation. The basal immunosuppression begins together with the desensitization.
Post transplantation apheresis is done with impaired graft function.
•Role of protocol biopsies
protocol biopsy at 1 and 2 years, C4d in peritubular capillaries was found with no sign of ABMR or transplant glomerulopathy
It is related to accommodation if not associated with abnormal graft function.
•Complications
-Surgical complications are the same to standard transplants.
– Hemorrhages are more common than standard transplantation.
The hemorrhages were significantly associated with the number of IA sessions.
-infectiouns related to the intensity of desensitization strategies.
-ABMR is the first cause of graft loss in transplantations involving ABOi. The risk for ABMR is related to the isoagglutinin level at transplantation and to the presence of anti-HLA antibodies.
•KPD; kidney paired donation is a good strategy to help 2 or more incompatible pairs to find more matched donor so avoid heavy immunosuppression with its complications.
The simplest model of the KPD is the two-way, it may expand to involve a higher numbers of pairs realizing the KPD at three-way, four-way, and so on.
•CONCLUSION
-ABOi renal transplantation is no more contraindicated and outcomes similar to the standard transplantations.
-ABOi transplants are more expensive than the ABOc transplants, however they are less expensive than dialysis.
– wider extension of KPD programmes will help to perform more compatible transplantation.
Current protocols and outcomes of ABO-incompatible kidney transplantation
Renal transplantation is considered the best therapy for patients affected by end-stage renal disease. However, approximately 30% of such transplantations are considered incompatible from the immunological point of view either because of the presence in the recipient of antibodies directed against the human leukocyte antigen (HLA) antigens of the donor or because of the incompatibility of the ABO system between the donor and recipient or because of both . There are two strategies to overcome these barriers:
(1) To desensitize the recipient to remove the antibodies .
(2) To exchange the organs between two or more pairs to exchange the organs between different donors.
IMMUNOLOGICAL ASPECTS
Indeed, better results in transplantation involving ABOi are obtained when transplanting kidneys from A2 donors to O recipients. The A2 subtype does not have circulating antigens linked to von Willebrand factor . The reaction of isoagglutinins with the antigens of the ABO group induces complement activation, as documented by the presence of C4d .In addition to its relation with the development of ABMR, the presence of C4d on the tissues may also be associated with the development of chronic rejection
DEVELOPMENT OF THE PRACTICE OF KIDNEY TRANSPLANTATION IN ABO- INCOMPATIBLE PAIRS For a long time, ABOi has been considered an absolute contraindication to kidney transplantation. For the first time, Brynger et al[9] reported the clinical outcomes of 21 renal transplantations from A2 donors to O recipients. Since then, several authors have tried to perform kidney transplantations in pairs with ABOi[10-13] . Principally after 1998, there was a worldwide increase in the rate of kidney transplantations from living donors that involved ABOi. This fact may be principally ascribed to four factors. (1) Since 1998, our knowledge of the diagnosis and treatment of ABMR has substantially improved. (2) By the beginning of 2000, Japanese authors published excellent results in renal transplantations involving ABOi[14] , although the main limitation of the Japanese strategy was the splenectomy associated with their pretransplantation protocol. (3) Later, Johns Hopkins University and the Mayo Clinic in the United States documented the possibility of performing such transplantation without splenectomy with the administration of an anti-CD20 monoclonal antibody (rituximab [RTX])[7,15] . (4) Finally, Swedish authors developed a new technique that demonstrated outcomes in renal transplantation involving ABOi that were similar to the outcomes of standard renal transplantation
TECHNIQUES OF ABO DESENSITIZATION AND DIFFERENT PROTOCOLS USED OVER TIME
CLINICAL OUTCOMES AFTER RENAL TRANSPLANTATION INVOLVING ABOI
Overall, transplants involving ABOi compared to those involving ABOc had a significantly higher mortality rates at 1, 3 and 5 years . Both graft losses and mortality in transplants involving ABOi became equivalent to ABOc transplants at 8 years after transplantation.
The higher mortality rate is probably a consequence of the high immunosuppression related to the therapy
Coagulation disorders were also frequent in transplant involving ABOi.
Polyoma virus nephropathy was also more frequent in patients receiving RTX
OPEN CONTROVERSIES IN KIDNEY TRANSPLANTATION INVOLVING ABOI
desensitization aims to modify the immunological reaction in different ways:
(1) Antibody reduction by plasmapheresis or IA.
(2) Inhibition of antibody production by splenectomy (old system) or by RTX.
(3) Pleiotropic action of IVIG.
(4) Complement inhibition by Eculizumab .
Main controversies
Apheresis technique used
Role of rituximab Utility and role of IVIG
Method to detect isoagglutinins quantity
Type of immunosuppression
Utility of posttransplantation apheresis
Accommodation
Role of protocol biopsies
Principal complications
KPD
KPD programs have several points that yet need to be better clarified.
The principals are as follows:
-For ESRD patients, to avoid a long time on dialysis, transplantation from living donor is the best option. However, approximately 30% ofsuch transplantations are considered incompatible from the immunological point of view either because of the presence in the recipient of antibodies directed against the HLA antigens of the donor or because of the incompatibility of the ABO system between the donor and recipient or because of both.
-There are two principal strategies to overcome these barriers:
(1) To desensitize the recipient to remove the antibodies and modify the immunological status, allowing the transplant.
(2) To exchange the organs between two or more pairs to exchange the
organs between different donors.
– Better results in transplantation involving ABOi are obtained when transplanting kidneys from A2 donors to O recipients. The A2 subtype does not have circulating antigens linked to the von Willebrand factor.
-The reaction of isoagglutinins with the antigens of the ABO group induces
complement activation, as documented by the presence of C4d.
– In addition to its relation to the development of ABMR, the presence of C4d on the tissues may also be associated with the development of chronic rejection.
-The most frequent protocols applied to obtain desensitization in pairs with ABOi are a mixture of the following strategies.
1.Removal of circulating ABO antibodies:
The removal of circulating ABO antibodies is obtained principally by plasmapheresis or immune-adsorption (IA). The aim of these strategies principally applied several days before transplantation, is to reduce the circulating anti-A/B antibody levels to achieve titers between 1:8 and 1:32.
2.Immunomodulation
This technique consists in the administration of high doses of polyclonal intravenous immunoglobulin (IVIG) to the patient before transplantation. The aim is to replace thepatient’s immunoglobulins lost because of apheresis techniques. In addition, IVIG blocks the Fc receptor and has immunoregulatory properties.
3 .B cell depletion
B cells produce isoagglutinins, and their reduction is essential to obtain effective
desensitization.
Historically, splenectomy has been used principally in Japan for B cell depletion. To date, RTX, a humanized monoclonal antibody that binds to CD20 expressed on the B cell membrane, is the drug used to obtain B cell depletion.
Independent of which strategy is used, the common aim is to reduce the agglutinin titer to a predetermined level.
-The phenomenon of lack of rejection in the presence of circulating ABO antibodiescomplement activating is known as accommodation and it is also
responsible for kidney protection over a long period of time.
-The most frequently used technique was the removal of circulating anti-ABO
antibodies by plasmapheresis .
More recently, principally in Europe, plasmapheresis has been replaced by
the technique of the IA of isoagglutinins using specific protein A or anti-human Ig
columns . The main advantages of this technique are to its high capacity to induce
ABO agglutinin removal with high biocompatibility and without complement
activation.
-Almost all desensitization strategies used the administration of IVIG to improve immunomodulation and the administration of RTX to avoid splenectomy.
-Attempts to reduce the RTX doses were made, as well as attempts to completely
omit RTX administration.
– Tailored desensitization strategy obtains good results with personalized therapy and lower costs.
-The results obtained after renal transplantation involving ABOi are generally good and overlap with the results obtained in ABOc renal transplantation.
-Overall, transplants involving ABOi compared to those involving ABOc had a
significantly higher mortality rates at 1, 3 and 5 years .
-Both graft losses and mortality in transplants involving ABOi became equivalent to ABOc transplants at 8 years after transplantation.
-The higher mortality rate is probably a consequence of the high immunosuppression related to the therapy. Coagulation disorders were also frequent in transplant involving ABOi.
-The use of a high dose of RTX or the use of other immunosuppressants to reach a higher desensitization was also associated with a higher mortality rate due to infectious disease.
-Polyoma virus nephropathy was also more frequent in patients receiving RTX, as
documented by several authors .
-Surgical complications in transplantations involving ABOi are similar to complications of standard transplants, except for hemorrhages. Hemorrhages are likely to be ascribed to the apheresis treatment.
-The hemorrhages were significantly associated with the number of IA sessions.
-ABMR is the first cause of graft loss in transplantations involving ABOi. The risk
for ABMR is related to the isoagglutinin level at transplantation and the presence of anti-HLA antibodies.The incidence of ABMR ranges between 10% and 30%.It principally occurs in the early post-transplantation, usually in the first 2 wk.
KPD
-The simplest model of the KPD is two-way, in which two pairs of donors and
recipients with ABOi exchange the kidneys, thereby resolving the incompatibility.
-With the increasing number of KPD programs, it has been possible to achieve a
global kidney exchange.
-A further increase in kidney exchanges was realized by the domino KPD, which
start from an altruistic donor and finish with the donation of a kidney to a recipient on the waiting list. A variant of domino KPD is the Never Ending Altruistic chain, which allows a higher number of recipients to be transplanted by the use of bridge donors .
Antigens and antibodies of ABO :
Antigens are glycoproteins found on RBCs, platelets, endothelial cells, and renal tubules.
anti A/B antibodies formed against these antigens with blood group O have both types of antibodies anti-A and anti B antibodies while blood group AB has no antibodies.
Different protocols used for desensitization for ABO :
A-Removal of circulating antibodies :
1- plasmapheresis :
Plasmapheresis with the exchange of plasma with other colloid plasma or albumin
With side effects of non-selectivity of removal of all immunoglobulins and increased risk of infection, hypocalcemia, and coagulation factors deficiency.
2- The double filtration plasmapheresis :
done by 2 plasma filters with fewer complications of plasmapheresis
3-IA :
Removing of IgG antibodies with two subtypes selective and non-selective
Selective only remove undesirable antibodies
B- Immunomodulation:
uses of high doses of IVIG to replace immunoglobulin lost during plasmapheresis
and block FC receptors, complement inhibition, inhibit B/T-cell proliferation, increase B cells apoptosis, and suppression of CD8 T-cell cytotoxicity.
C-B cell depletion :
Splenectomy: the concept dependant that the spleen is the reservoir for both B cells and plasma cells
Splenectomy has been largely abandoned and replaced by Rituximab
due to increased risk of sepsis with encapsulated organisms, pancreatic leakage, and portal vein thrombosis.
Rituximab:
as it leads to depletion of B cells by binding to CD20 on these cells.
side effects: fever, chill, headache, and nausea
dose: 375mg/m2 1 month before KT
Different protocols used for desensitization :
in Europe IA is used more frequently than PP as high selectivity, capacity for removal of A/B antibodies and to avoid complications resulting from PP
and dose of Rituximab added 1 month before KT and one dose of IVIG 0.5 gm/kg one day before ABOi-KT
More recently, at the Guy’s Hospital :
ABO titer of 8 or less: only Rituximab was used
and of titer 16and 64: Rituximab + PP were used
and titer > 64: Rituximab + IAs were used
Immunosuppression :
immunosuppression in kidney transplantation with ABOi-KT is the same used in ABOc-KT but high risk of ABMR during steroid withdrawal.
Post-transplantation apheresis:
indicated for patients presented with allograft dysfunction with the presence of a high titer of anti-A/B antibodies.
Accommodation :
despite an increase of Incompatible antibodies post-transplant, these make no harm due to the Accommodation phenomenon as based on less avidity, specificity of antibodies, and change of structure of antigens.
Clinical Outcomes in ABOI-KT :
Higher mortality rates in ABOi-KT more than in ABOc-KT at 1, 3, and 5 years
with no difference in mortality rates at 8 years
Complications:
surgical complications were the same as ABOc-KT but increased risk of hemorrhage due to loss of coagulation factors during PP
Infections: increase risk of infections of BK, CMV, HSV, sepsis, and UTI.
ABMR increases the risk of ABMR in ABOi-KT( ranges between 10% and 30%)
Desensitization V.S KPD:
KPD will be a good choice if available due to its low cost, no need for desensitization, and low immunological risk.
Conclusion :
ABOi-KT has a high cost than the ABOc-KT, however, they are less expensive than dialysis.
the ABOi kidney transplantation became available due to advances in desensitization protocols used for the removal of A/B antibodies
KPD should be increased to increase the number of transplants
INTRODUCTION
The presence in the recipient of antibodies directed against the human leukocyte antigen (HLA) antigens of the donor or because of the incompatibility of the ABO system between the donor and recipient or because of both makes transplantation a hard job. Better options included desensitization and kidney paired donation programs.
IMMUNOLOGICAL ASPECTS
At the renal level, glycoproteins are expressed on the collecting and distal tubules and on the vascular endothelial cells. The intensity of antigen expression on the tissues is also related to the acute rejection rate in patients with low isoagglutinin levels in the blood.
Group O individuals have higher antibody titers to both the A and B antigens. So, they have a higher incidence of
Antibody-mediated rejection (ABMR) after transplantation.
The reaction of isoagglutinins with the antigens of the ABO group induces complement activation, as documented by the presence of C4d.
TECHNIQUES OF ABO DESENSITIZATION
Removal of circulating ABO antibodies
Principally by plasmapheresis or immune-adsorption (IA) to achieve titers between 1:8 and 1:32.
Immunomodulation
Using high doses of polyclonal intravenous immunoglobulin (IVIG) to the patient before transplantation. It blocks the Fc receptor and has immunoregulatory properties.
B cell depletion
RTX, a humanized monoclonal antibody that binds to CD20 expressed on the B cell membrane is now the drug of choice.
The transplanted kidney develops in approximately 2 wk. the capacity to resist complement-mediated damage. The phenomenon of lack of rejection in the presence of circulating ABO antibodies complement activating is known as accommodation.
A tailored desensitization strategy obtains good results with personalized therapy and lower costs.
CLINICAL OUTCOMES AFTER RENAL TRANSPLANTATION INVOLVING
ABOI
Transplants involving ABOi compared to those involving ABOc had a significantly higher mortality rates at 1, 3 and 5 years.
Both graft losses and mortality in transplants involving ABOi became equivalent to ABOc transplants at 8 years after transplantation.
The higher mortality rate is probably a consequence of the high immunosuppression related to the therapy.
Coagulation disorders were also frequent in transplant involving ABOi that were related to the modifications in the coagulation system induced by plasmapheresis or IA.
The use of a high dose of RTX or the use of other immunosuppressants to reach a higher desensitization was also associated with a higher mortality rate due to infectious disease.
Polyoma virus nephropathy was also more frequent in patients receiving RTX.
Immunosuppression
The basal immunosuppression begins together with the desensitization.
Post-transplantation apheresis
It is reserved for patients who present abnormalities of graft function together with isoagglutinin rebound.
Accommodation
In the presence of circulating antibodies and antigens on the graft cell surface, the graft itself may not be rejected.
Accommodation in renal transplantation involving ABOi has been defined as the presence of circulating isoagglutinins and antigens on the graft cells with normal renal function and normal histology. The mechanism is thought to be due to the presence of a low titer of antibodies, with low affinity and with the blockage of complement activation.
Under these conditions, endothelial cells develop a phenotypic change according to which they become resistant to antibody damage. Eculizumab, a monoclonal antibody against C5, may facilitate accommodation. It may represent a rescue therapy in the case of severe ABMR.
Role of protocol biopsies
C4d in peritubular capillaries was found with no sign of ABMR or transplant glomerulopathy. It is related to accommodation.
Complications
Surgical complications in transplantations involving ABOi are similar to complications of standard transplants, with the exception of hemorrhages related to the apheresis treatments.
ABMR principally occurs in the early post-transplantation, usually in the first 2 wk.
CONCLUSION
Programs of paired kidney donation are worldwide need to be verified and validated.
Current protocols and outcomes of ABO-incompatible kidney transplantation
Kidney transplantation is the best treatment for ESRD patients. To date, many challenges facing this treatment in addition to cadaveric donor shortage. Contributing to the increase in the number of patients on the waiting list. Immunological reactivity represents one of these challenges. Transplantation from the living donor is the best option to avoid a long time on dialysis. However, about 30% of these transplantations are immunologically incompatible, either due to the presence of DSA in the recipient serum that is directed against the human leukocyte antigen (HLA) antigens of the donor or due to the incompatibility of the ABO system between the donor and recipient or because of both. To overcome these barriers there are two strategies: (1) desensitization of the recipient to remove the DSA to allow transplantation or (2) paired kidney exchange strategy.
Immunological Aspects
The ABO system consists of glycoprotein antigen expressed on the erythrocyte membrane, epithelial and endothelial cells. in the kidney, this antigen is expressed on the collecting and distal tubules and on the vascular endothelial cells. the intensity of them is related to the acute rejection.
The ABO groups are A, B, AB, and O types. The antibodies against ABO antigens are formed against the antigen that is not native to the host. Group O individuals have higher antibody titers to both the A and B antigens, consequently, they have a higher incidence of ABMR after transplantation. The ABO system antigens have two forms; membrane-linked antigens and circulating epitopes A and B soluble and linked to Von Willebrand factor exist in some patients. These antigens when free, can cause ABMR. For ABOi transplantation better results were obtained between A2 donors and O recipients. As A2 subtype does not have circulating antigens linked to Von Willebrand factors. The reaction of isoagglutinins with the antigens of the ABO group causes complement activation, with C4d deposition on the tissues indicating ABMR.
Development of the practice of kidney transplantation in ABO-Incompatible pairs:
Brynger et al, were the first to report ABOi transplantation between A2 donors and O recipients.
Since 1998; the ABOi kidney transplantation has been increased worldwide. As our knowledge of the diagnosis and treatment of ABMR improved as well different successful protocols exist. Like Japanese authors’ strategy although splenectomy was the main limitation of it. Johns Hopkins University and Mayo clinic strategy that includes the anti0CD20 monoclonal antibody (rituximab instead of splenectomy). Swedish authors also published new techniques with a good outcomes.
TECHNIQUES OF ABO DESENSITIZATION AND DIFFERENT PROTOCOLS USED OVER TIME
Most protocols are mixture of the following strategies:
Removal of circulating ABO antibodies
This is done by plasmapheresis or immune-adsorption (IA). This therapy is carried out several days before transplantation. aimed to reduce circulating anti-A/-B antibody levels to below 1:8 and 1:32
The therapeutic plasma exchange using highly permeable membranes allows elimination of 20% of the circulating antibodies by session, but it also remove other proteins like protective antibodies and coagulation factors. This is evoluted to more advanced technique using double filtration membranes, in which the second membrane allows smaller molecules to return back to the patient, thus avoiding many complications of the previous therapeutic plasma exchange.
For immune adsorption there are different types of columns:
1- IA with immobilized antibodies:
It is the most widely used method. A Therasorb column contains:
a- polyclonal sheep anti-human IgG antibodies, remove IgG Abs effectively.
b- Staphylococcal protein A bound to sepharose, is effectively remove IgG of different classes. In addition, they are capable of inducing a B cell apoptosis, so enhancing the immunosuppression.
2- IA technique uses immobilized antigens and synthetic epitopes:
This is more specific, removing only the undesirable antibodies.
Immunomodulation
It consists of the administration of high doses of polyclonal IVIG before transplantation. to replace the immunoglobulin lost by plasmapheresis, also it blocks the FC receptor and has immunoregulatory properties.
B cell depletion
The isoagglutinin are produced by B cells, so depletion of B cell is an essential step in the desensitization. Historically; this was done by splenectomy in Japanese protocol. Newly, rituximab, anti-CD20 monoclonal antibody used to obtain B cell depletion.
All methods aim to reduce ABO antibody titer. The transplanted kidney when exposed to a low titer of circulating antibodies, acquires in 2 weeks the capacity to resist complement-mediated damage. A phenomenon is called accommodation. Lack of rejection in the presence of circulating ABO antibodies complement activation.
Almost all desensitization strategies use the administration of IVIG to improve immunomodulation and the administration of rituximab to avoid splenectomy.
CLINICAL OUTCOMES AFTER RENAL TRANSPLANTATION INVOLVING ABOI
The ABOi renal transplantation outcomes are generally good and overlap with ABOc renal transplantation. although these results were obtained from studies including a small number of patients and they were unable to compare different therapies. Further research should be conducted on which pre-transplantation therapies should be adopted.
Overall, the evidence of the benefits of different preconditioning therapies is low.
A new wider systemic review study including a large number of patients shows that ABOi transplants had a significantly higher mortality rate at 1, 3, and 5 years compared to those involving ABOc. While at 8 years both graft losses and mortality in ABOi transplant group become equivalent to ABOc transplants.
The higher mortality rate in ABOi transplants is probably related to the side effects of high immunosuppression that increase the incidence of infection. Polyomavirus nephropathy was more prevalent in the rituximab group.
OPEN CONTROVERSIES IN KIDNEY TRANSPLANTATION INVOLVING ABOI
ABOi transplants still carry many controversies. The majority of these controversies involve the strategies of desensitization. That involves plasmapheresis, splenectomy (old way), or rituximab, pleiotropic action of IVIG, complement inhibition by eculizumab.
Technique of apheresis
The number of plasmapheresis differs depending on the basal levels of isoagglutinins and the centre experience.
Role of Rituximab (RTX)
Its sued allowed avoidance of splenectomy. The use of rituximab reduces the risk of isoagglutinin rebound and the risk of ABMR as well reduces the chronic rejection. It is given 1 month before transplantation.
IVIG
It acts through (1) blockage of Fc receptor on the leukocyte membrane, (2) inhibition of the complement activation, and (3) inhibition of the circulating antibodies against HLA. It reduces antibody rebound after transplantation and ABMR risk.
Isoagglutinin quantification
Isoagglutinin titer determination is necessary to decide on the immunosuppression and in particular the apheresis technique to be used.
Immunosuppression
The immunosuppression in ABOi transplantation is similar to that used for standard transplantation. overall, patients receiving ABOi transplantation are not allowed to reduce immunosuppression.
Post-transplantation apheresis
Patients who develop graft function abnormality together with isoagglutinin rebound receive apheresis treatment.
Accommodation
Phenomenon involves the presence of circulating antibodies and antigens on the graft cell surface, in the presence of normal graft function and histology (i.e no rejected). This phenomenon seems to be due to low titer antibodies, low affinity and complement blockade. By this, the endothelial cells develop resistance to antibody damage. The accommodation can be facilitated by reduction of the isoagglutinin titer by rituximab, IA specific columns, and complement activation blockade.
Eculizumab is a monoclonal antibody against C5, facilitates accommodation, and allows ABOI transplantation. it may be used as rescue therapy in severe ABMR.
Role of protocol biopsies
The presence of C4d in protocol biopsies of ABOi renal transplants seems to be related to accommodation when found in the absence of clinical or histological abnormalities.
Complications:
Surgical complications in ABOi transplantations are similar to standard transplants. Haemorrhages are common that are likely to be related to the apheresis treatment. Infectious complications were significantly related to the number of IA sessions and the intensity of desensitization strategies.
ABMR is the first cause of graft loss and it is related to the isoagglutinin level at transplantation and to the presence of anti-HLA antibodies.
Kidney Paired Donation
Develop to overcome the immunologic barrier to transplantation. it ranges from the simplest model of the KPD that involves two pairs of donors and recipients to domino KPD which starts with an altruistic donor and finishes with the donation of a kidney to a recipient on the waiting list.
MAKING A CHOICE BETWEEN DESENSITIZATION AND KPD
It remained to be answered by the availability of KPD in a short time. That depends on the organization. KPD is generally cheaper than desensitization. Overall, the KPD is growing, while the desensitization strategy is dropping.
Conclusion
The ABOi renal transplantation is possible with the use of a desensitization strategy by which the immunological barrier of different ABO groups has been overcome.
This success is attributed to the accommodation as well to the achievement of some humoral tolerance. No standardized apheresis protocol has been agreed to. And researches are in needs to answer the question in regards of best desensitization protocols, the role of rituximab, the significance of C4d in the graft with normal function and the accommodation phenomenon role.
ABOi expansive therapy as compared to ABOc transplantation and KPD represents an option to decrease this cost but it needs good organization at the national and international levels to increase the probability to find a suitable donor. Worldwide, KPD has substantially increased, therefore, increasing the number of transplants. A wide national registry for PKD would be used instead of small registries to increase transplants.
Transplantation is the treatment of choice for ESRD patients and living donor transplant is better alternative to compensate for shortage of deceased donor pool patients with ESRD, but around 30% of patients are sensitized –PKD program and desensitization will help to solve this issue.
IMMUNOLOGICAL ASPECTS
Blood group antigens are presented on RBCS , endothelial cells and renal tubular epithelial cells in certain circumstances, they include A, B, AB, O . Patient with blood group A has anti B antibodies, while those with blood group B has anti -B antibodies.Individuals with blood group O has no antibodies so they are universal donors. However, patients with blood group AB are universal recipient. Blood group A has 2 subtypes: A1 (80 %) and A2 (20%, less immunogenic). Recipients with anti-A sera ( those with blood group B, O) can receive kidneys from donors with blood group A2 if anti-A sera is low. Individuals with blood group A2 can serve as universal donors but only if the titer of antibodies is low
TECHNIQUES OF ABO DESENSITIZATION AND DIFFERENT PROTOCOLS USED OVER TIME
B cell depletion is done by Rituximab which was done by splenectomy in the past. Some protocols do not used rituximab at all if patient had reached an anti-A/B antibody titer of less than 1:32 with good graft survival. An absence of detectable splenic B cells occur after rituximab administration,but plasma cells remain as they lack CD20 receptors. The specific dose of rituximabis not clear and is given four weeks prior to the scheduled transplant surgery date.
Antibodies removal
Removal of circulating ABO antibodies
Plasmapheresis removes 20% of antibodies in a session along with coagulation factors leading to bleeding tendency and remove all IgG with higher risk of infection and sepsis.
Double filtration plasmapheresis uses second filter which allows return of essential components to the blood and has fewer complications.
IA selectively eliminates humoral factors using immobilised Ab or immobilised staph protein A or immobilized antigens and synthetic epitopes with the least side effects (produce 2-4 fold titer reduction per session), but more expensive than plasmapheresis and not widely available.
Isoagglutinin titer is assessed 2 weeks before transplantation. The goal is to achieve isoagglutinin titer of ≤1:8
Immunomodulation
Using IVIG having immunomodulatory role and acts as an immunomodulator by blocking Fc receptors , so it prevents the rebound increase in antibody by plasma cells, moreover IVIG aid in the replacement of immunoglobulins that are removed during PE or IA. IVIG is usually given after plasmapharesis, but one regimen is to give 0.5 gm/kg in 1 dose the day before transplantation or in 2 doses 4 and 1 day before transplantation
There is no standard protocol for desensitization prior to transplantation, but in general, we can give rituximab 2 weeks prior to transplantation and do plasmapheresis 4 sessions 1 week before operation and continue it for another 3-4 sessions post transplant, induction using either basiliximab or ATG according to other risk factors-tacrolimus ,MMF and steroid were given from 2-7 days prior to transplantation, keeping trough level of tacrolimus from 12-15 ng/ml.
CLINICAL OUTCOMES AFTER RENAL TRANSPLANTATION INVOLVING ABOI
Overall, transplants involving ABOi compared to those involving ABOc had a significantly higher mortality rates at 1, 3 and 5 years. The higher mortality rate is probably a consequence of the high immunosuppression related to the therapy. Indeed, some studies in which selected patients received a lower, tailored desensitization therapy reported an improved survival rate, with fewer infections and without ABMR.
Accommodation:
It is lack of rejection in presence of circulating ABO antibodies with normal kidney function and normal histology and is facilitated by reduction of isoagglutinin levels, blocking of complement activation and rituximab. No role of protocol biopsies as far as ABO incompatible transplants are concerned.
Complications:
Hemorrhage is more common in ABOi transplants, significantly associated with number of IA sessions.
Infectious complications have different incidence in different studies mostly vary according to intensity of desensitization.
AMR, the main cause of graft loss, related to level of isoagglutinin level at transplantation and presence of anti-HLA antibodies
KPD :
Simplest model of the KPD -two-way, in which two pairs of donors and recipients with ABOi exchange the kidneys, thereby resolving the incompatibility.
A variant of domino KPD is the Never Ending Altruistic chain, which allows a higher number of recipients to be transplanted by the use of bridge donors .
Making a choice between desensitization and KPD
KPD is cheaper but may be associated with prolonged waiting time.
Costs of KPD is similar to ABOc kidney transplants
According to data from US, overall KPD is increasing while desensitization strategies are decreasing.
Blood group antigens are present in RBCS and in the endothelial cells including A, B, AB, O
Patient having blood group A have antibodies against B antigen ,and those with blood group B has anti -A antibodies
Individuals with blood group O have no antibodies so considered universal donors, and patients with blood group AB are universal recipient.
Blood group A is subdivided into A1 and A2. A2 antigen accounts for 20 % of white race individuals with blood group A, and is less expressed on RBCS than A1 ; recipients with anti-A sera ( those with blood group B, O) can receive kidneys from donors with blood group A2 if anti-A sera is low; ie individuals with blood group A2 can serve as universal donors with low titer of antibodies.
Desensitization protocols
– B cell depletion
* splenectomy is replaced by rituximab due to its side effects including infection with encapsulated organisms & surgical complications
*Rituximab produce splenic B cell depletion decreasing risk of rebound, but it spares plasma cells since they contain no CD20 receptors, so its benefit is uncertain
*Aiming to reduce cost, trials were done to reduce use of Rituximab or remove it from desensitization protocols or give it only on demand ; if titer > 1/16 with a good outcome:
– 35% of desensitization protocols are using Rituximab
– Antibodies depletion
*PP (remove 20 % of antibodies per session), less effective, remove also coagulation factors resulting in bleeding tendency
*Double filter plasmapheresis, with fewer complications as a second filter is used which allows for the return of small molecules
* IA which is a specific technique that selectively removes IgG with the least side effects (produce 2-4 fold titer reduction per session), but more expensive ( 2-3 times more than plasmapheresis)
– IVIG
Immunosuppression
Monitoring
Outcome
Complications include bleeding ( the most common surgical complications related to ABO I transplantation ), increase in risk of infections and sepsis in ABOi compared to compatible transplantation and significant increase in the risk of ABMR in patients with ABOi transplantation
ABO I transplantation is considered expensive.
Transplantation of living donor is an option to avoid long term dialysis complications but obstacles are faced including immunological barrier, which could be HLA and or ABO incompatibility , in order to solve this problem 2 strategies are applied which are desensitization and paired kidney exchange program.
The most frequent protocols:
Removal of circulating ABO antibodies
Immunomodulation
B cell depletion
Clinical outcomes after Renal Tx of ABOi cases
According to Anti A /B Ab titer desensitization protocols are
Mortality rate is higher in ABOi Tx than ABO c Tx at 1,3 ,5 years could be due to extensive immunosuppression , coagulation disorders and infectious complications ,while graft loss and mortality is equal in both groups at 8 years post transplantation
Controversies in ABO i Tx
Technique of apheresis
The high cost of specific columns used because it is efficient than other columns lead to reusage of those specific columns
It seemed that aphaeresis could be benefice even in cases with low Ab titers to decrease inflammatory molecules level
RTX role
It replaced splenectomy , it lowers the risk of isoagglutin rebound , the risk of ABMR and the risk of chronic rejection.
IVIG
It blocks FC receptor on leucocytes, inhibit complement activation and HLA Ab, also it decreases Ab rebound after Tx ,decreasing ABMR risk
Isoagglutinin quantification
Detected by flux cytometry , tube and gel technique .
On the other hand it has no predictive value for ABMR.
Immunosuppression
For ABOi cases is the same as for standard transplantation. It starts with the desensitization.
Post-transplantation apheresis
Is done for patients with abnormalities of graft function and with isoagglutinin rebound
Accommodation
Is the presence of circulating isoagglutinin and antigens on the graft cells with tolerance and less rejection risk due to due to the presence of a low titer of antibodies, with low affinity and with the blockage of complement activation.
Eculizumab can enhance accommodation.
Protocol biopsy role
Complications
Kidney paired donation (KPD)
National Kidney Registry in the United States, revealed that KPD is increasing , while the desensitization strategy is decreasing
INTRODUCTION
Approximately 30% of such transplantations are considered incompatible from the immunological point of view either because of the presence in the recipient of antibodies directed against the human leukocyte antigen (HLA) antigens of the donor or because of the incompatibility of the ABO system between the donor and recipient or because of both. There are two principal strategies to overcome these barriers: (1) To desensitize the recipient to remove the antibodies and modify the immunological status, allowing the transplant; and (2) To exchange the organs between two or more pairs to exchange the organs between different donors. The aim of this review is to give a general overview of ABO incompatibility (ABOi), the techniques used to overcome ABOi, the removal of the immunological barriers, and the outcomes obtained. In the last part of the review, kidney paired donation (KPD) will also be briefly discussed.
IMUNOLOGICAL ASPECTS
The reaction of isoagglutinins with the antigens of the ABO group induces complement activation, as documented by the presence of C4d. In addition to its relation with the development of ABMR, the presence of C4d on the tissues may also be associated with the development of chronic rejection.
TECHNIQUES OF ABO DESENSITIZATION AND DIFFERENT PROTOCOLS USED OVER TIME
Removal of circulating ABO antibodies
The removal of circulating ABO antibodies is obtained principally by plasmapheresis or immune-adsorption (IA). The aim of these strategies, principally applied several days before transplantation, is to reduce the circulating anti-A/B antibody levels to achieve titers between 1:8 and 1:32.
Among the techniques used to induce desensitization, the apheretic techniques are those with the most relevant evolution since the beginning. The simpler, cheaper, but less effective technique has been the therapeutic plasma exchange using highly permeable membranes. The procedure eliminates approximately 20% of the antibodies by session. Additionally, removes protective antibodies and coagulation factors. The double filtration plasmapheresis is performed by two plasma filters, and the second one allows smaller molecules to return back to the patient, avoiding many complications associated with the therapeutic plasma exchange.
A further evolution has been made by the use of columns for the selective removal of humoral factors by IA. A Therasorb column contains polyclonal sheep anti-human IgG antibodies and is effective in removing IgG antibodies. A different IA technique uses immobilized staphylococcal protein A. These Immunosorba columns, that contains staphylococcal protein A bound to sepharose is effective in removing IgG of different classes. Additionally, are able to induce a B cell apoptosis, so enhancing the immunosuppressive effect. Another IA technique uses immobilized antigens and synthetic epitopes and is the most specific technique in removing only the undesirable antibodies
Immunomodulation
This technique consists in the administration of high doses of polyclonal intravenous immunoglobulin (IVIG) to the patient before transplantation, blocking the Fc receptor and has immunoregulatory properties.
B cell depletion
B cells produce isoagglutinins, and their reduction is essential to obtain effective desensitization. Historically, splenectomy has been used principally in Japan for B cell depletion. To date, RTX, a humanized monoclonal antibody that binds to CD20 expressed on the B cell membrane, is the drug used to obtain B cell depletion.
When exposed to a low ABO antibody titer, the transplanted kidney develops in approximately 2 wk the capacity to resist complement-mediated damage. The phenomenon of lack of rejection in the presence of circulating ABO antibodies complement activating is known as accommodation. Accommodation is also responsible for kidney protection over a long period of time.
In the literature different protocols exist that have been changed over time, so advantages and disadvantages need to be discussed.
CLINICAL OUTCOMES AFTER RENAL TRANSPLANTATION INVOLVING ABOI
The results obtained after renal transplantation involving ABOi and reported in this review are generally good and overlap with the results obtained in ABOc renal transplantation. However, the results reported generally refer to studies with a low number of patients.
Overall, the evidence of the benefits of the different preconditioning therapies is low, although it seems that patients receiving the newest therapies have a better outcome with fewer severe side effects.
Overall, transplants involving ABOi compared to those involving ABOc had a significantly higher mortality rates at 1, 3 and 5 years ( P < 0.0001). Both graft losses and mortality in transplants involving ABOi became equivalent to ABOc transplants at 8 years after transplantation.
The higher mortality rate is probably a consequence of the high immunosuppression related to the therapy. Excess immunosuppression is the cause of severe bacterial or viral infections.
Coagulation disorders were also frequent in transplant involving ABOi. This complication is probably related to the modifications in the coagulation system induced by plasmapheresis or IA. The use of a high dose of RTX or the use of other immunosuppressants to reach a higher desensitization was also associated with a higher mortality rate due to infectious disease.
Polyoma virus nephropathy was also more frequent in patients receiving RTX, as documented by several authors. All of these findings on the higher mortality rate in transplants involving ABOi, probably related to the side effects of high immunosuppression are in favor of tailored immunosuppression. Indeed, some studies in which selected patients received a lower, tailored desensitization therapy reported an improved survival rate, with fewer infections and without ABMR.
OPEN CONTROVERSIES IN KIDNEY TRANSPLANTATION INVOLVING ABOI
The different and discordant results reported by the different authors highlight the controversies that are still open in kidney transplantation involving ABOi. The vast majority of controversies concern the strategies of desensitization.
Technique of apheresis
The costs of IA are 2-3 times higher than those of plasmapheresis. Some studies have suggested the reuse of columns to reduce the costs.
The number of apheresis treatments differs according to the basal levels of isoagglutinins and the center. Almost all centers try to reach a titer of 1:8 before transplantation. A relevant question is what to do with patients with a low titer of isoagglutinins. Several centers have reported good results in these patients with few or no apheresis treatments.
Role of RTX
The use of RTX has allowed the avoidance of splenectomy since 2002. The use of RTX in kidney transplantation involving ABOi does not seem to be necessary in all patients. In the meta-analysis already mentioned, only 35% of patients were treated with RTX. The use of RTX reduces the risk of isoagglutin rebound and the risk of ABMR. In addition, the risk of chronic rejection seems to be reduced by the use of RTX.
IVIG
Among the various effects of IVIG on the immune reaction, the most common are: (1) Blockage of the Fc receptor on the leukocyte membrane; (2) Inhibition of the complement activation; and (3) Inhibition of circulating antibodies against HLA. In transplants involving ABOi, the IVIG administration reduces the antibody rebound after transplantation and the risk of ABMR.
Isoagglutinin quantification
To decide on the immunosuppression and in particular the apheresis technique to be used, it is necessary to know the isoagglutinin titer. The best method is flux cytometry , even if the method has a high cost. The tube and gel techniques for ABO antibody titration are also frequently used. However it should be highlighted that both the antibody basal titer before desensitization and the post-transplantation titer have a low predictive value for ABMR.
Immunossupression
The possibility of steroid withdrawal is discussed. Some studies have documented a high risk of ABMR in the case of steroid withdrawal soon after transplantation. Other studies have documented a high risk for acute rejection even in the case of late withdrawal . Overall, patients receiving transplant involving ABOi are not allowed to reduce immunosuppression.
Post-transplantation apheresis
Apheresis treatments post-transplantation are reserved for patients who present abnormalities of graft function together with isoagglutinin rebound. It does not attain beneficial effects in patients without graft dysfunction.
Accommodation
Accommodation in renal transplantation involving ABOi has been defined as the presence of circulating isoagglutinins and antigens on the graft cells with normal renal function and normal histology. By 2006, the American Society of Transplantation established a consensus on the accommodation status and added the presence of C4d on the peritubular capillaries . The pathogenesis of the accommodation seems to be due to the presence of a low titer of antibodies, with low affinity and with the blockage of complement activation. Under these conditions, endothelial cells develop a phenotypic change according to which they become resistant to antibody damage.
Eculizumab, a monoclonal antibody against C5, may facilitate accommodation. In addition, eculizumab may allow a safe transplantation in patients with ABOi with high antibody titers and may represent a rescue therapy in the case of severe ABMR.
Role of protocol biopsies
In summary, the presence and the role on protocol biopsies of C4d in transplantations involving ABOi seems to be related to accommodation when found in the absence of clinical or other histological abnormalities.
Complications
Surgical complications in transplantations involving ABOi are similar to complications of standard transplants, with the exception of hemorrhages. Hemorrhages are likely to be ascribed to the apheresis treatments.
The hemorrhages were significantly associated with the number of IA sessions.
The incidence of infectious complications is different across the studies. The difference is probably related to the intensity of desensitization strategies (the number and type of apheresis treatments and the dose of RTX, IVIG and other immunosuppressants).
ABMR is the first cause of graft loss in transplantations involving ABOi. The risk for ABMR is related to the isoagglutinin level at transplantation and to the presence of anti-HLA antibodies.
KIDNEY PAIRED DONATION ( KPD)
The hypothesis of overcoming the immunological barriers in a different way without the desensitization. The simplest model of the KPD is the two-way, in which two pairs of donors and recipients with ABOi exchange the kidneys, thereby resolving the incompatibility . The model may also include a higher numbers of pairs realizing the KPD at three-way, four-way, and so on. Several programs exist worldwide and with the increasing number of KPD programs, it has been possible to achieve a global kidney Exchange.
KPD programs have several points that yet need to be better clarified. The principals are as follows:
-Transportation of kidneys vs donor travel: This happens when two or more transplant centers are involved. The travel of the donor has a cost, and the donor will be operated on by an unknown surgical team. The travel of the organ minimizes the costs and allows the continuity of donor care.
-Simultaneous vs no simultaneous exchanges: Simultaneous donation has the advantage that no donor will change his mind. The drawback of simultaneous donations is logistical, principally if multiple organ donors will be operated on in the same center.
-Closed chains vs open chains: The channels of transplantations initiated by a non- donor may be extended but should end with donation to a recipient on the waiting list .
MAKING A CHOICE BETWEEN DESENSITIZATION AND KPD
KPD is generally cheaper with respect to desensitization, it remains to be answered the availability of KPD in a short time. This fact depends by the hospital or the national organization. The kidney exchange may base on a single center strategy, on a regional strategy on a national or international strategy.
CONCLUSION
The immunological barriers represented by the different ABO groups have been overcome. The two mechanisms responsible for this success are the accommodation and the achievement of some humoral tolerance. The most important techniques are those of desensitization and of isoagglutinins removal. In this field a relevant role have the immunoadsorption and the use of anti CD20 antibodies that allowed avoiding the splenectomy.
Finally, it should be also considered that though the ABOi transplants are more expensive than the ABOc transplants, however they are less expensive than dialysis.
Renal transplantation is considered the best therapy for ESRD patients. There are many problems that hinder this process such as cadaveric renal donor shortage, advanced age, immunological reactivity, or issues related to surgery or cardiovascular disease.
approximately 30% of such transplantations are considered incompatible either because of HLA or ABO incompatibility.
There are two principal strategies to overcome these barriers:
Development of the practice of ABOi Tx:
ABOi has been considered an absolute contraindication to kidney transplantation. For the first time.
Brynger et al reported the clinical outcomes of 21 renal transplantations from A2 donors to O recipients.
Principally after 1998, there was a worldwide increase in the rate of kidney transplantations from living donors that involved ABOi, this is due to the improvement of knowledge of the diagnosis and treatment of ABMR, results of a Japanese study of ABOi Tx, Johns Hopkins University and the Mayo Clinic documented the possibility of performing such transplantation without splenectomy with the administration of rituximab, Swedish authors developed a new technique that demonstrated outcomes in renal transplantation involving ABOi that were similar to the outcomes of standard renal transplantation.
Techniques of ABO desensitization and different protocols used over time:
Obtained through either PP or IA.
The aim is to reduce the circulating anti-A/B antibody levels to titers between 1:8- 1:32.
Consists of the administration of high doses of IVIG.
The aim is to replace the patient’s Ig that is lost because of the apheresis technique.
Previously, this was done by splenectomy, nowadays it is replaced by rituximab.
Clinical outcomes of ABOi Tx:
The results of ABOi Tx are generally good and overlap with the results obtained from ABOc Tx.
Most of the studies in this field are small with the exception of Barrett’s study.
Two systematic reviews and meta-analyses were done in this field but their limitation was the absence of RCTs, they only highlight the possibility that rituximab & IA could have superior efficacy.
A more recent systematic review showed that in ABOi Tx higher mortality rates at 1,3, and 5 years but mortality and graft loss become equivalent to ABOc Tx at 8 years. both coagulation disorders and BK virus nephropathy were higher in ABOi Tx.
Open controversies in ABOi Tx:
The different and discordant results reported by the different authors highlight the controversies that are still open in kidney transplantation involving ABOi. The vast majority of controversies concern the strategies of desensitization.
Technique of apheresis:
Whether to use specific or non-specific column IA, the no. of apheresis treatment, and what to do with a low titer of isoagglutinin.
Role of rituximab:
The use of rituximab helps to avoid splenectomy, however, not all patients require its use, but it reduces antibody rebound and the risk of ABMR, and also it reduces the risk of chronic ABMR.
IVIG:
It reduces antibody rebound after transplantation, and different protocols are used for its dose.
Isoagglutinin quantification:
Both the antibody basal titer before desensitization and the post-transplantation titer has a low predictive value for ABMR.
Immunosuppression:
Regarding steroid withdrawal, Some studies have documented a high risk of ABMR in the case of steroid withdrawal soon after transplantation. Others showed a high risk for acute rejection even in the case of a late withdrawal.
Post-transplant apheresis:
According to several authors, the treatment by apheresis post-transplantation does not attain beneficial effects in patients without graft dysfunction, while others perform post-transplantation apheresis in patients with isoagglutinin rebound or with high basal levels of antibodies.
Accommodation:
Is the presence of circulating isoagglutinin and antigens on the graft cells with normal renal function and normal histology.
The pathogenesis of the accommodation seems to be due to the presence of a low titer of antibodies, with low affinity and with the blockage of complement activation, so endothelial cells become resistant to antibody damage.
This process is facilitated by the reduction of the isoagglutinin level, RTX, IA- specific columns, and Eculizumab.
Role of protocol biopsies:
Studies showed that there is no difference in the histological pattern for patients with protocol biopsies done at 3 & 12 months post-transplant.
Complications:
Surgical complications are similar to complications of standard transplants, with the exception of haemorrhages.
The incidence of infectious complications is different across the studies.
ABMR is the first cause of graft loss & occurs usually in the first 2 wk post-transplant.
KPD:
The simplest model of the KPD is two-way, in which two pairs of donors and recipients with ABOi exchange the kidneys, and there are other forms such as 3 or 4 ways.
Several programs exist worldwide, and it has been possible to achieve a global kidney exchange.
Further increase in kidney exchanges was realized by the domino KPD, which starts from an altruistic donor and finishes with the donation of a kidney to a recipient on the waiting list.
KPD programs have several points that yet need to be better clarified:
Making choice between desensitization and KPD depends on the hospital or the national organization.
Each of the four ABO blood types belongs to one of the four categories (A, B, AB and O). Antigens that are not native to the host are responsible for the development of anti-blood group antibodies. Individuals belonging to Group O exhibit greater antibody titers against both the A and B antigens.
Patients in Group O have greater anti-A/B antibody titers, which leads to a higher incidence of AMR after transplantation, while kidneys from A2 donors to O recipients had better outcomes.
-It was discovered that ABOi was a contraindication to kidney transplantation, which led to the development of kidney transplantation practices in ABOi couples.
However, the number of ABOi transplants has grown globally as a result of AMR diagnosis and therapy is becoming more accurate.
It was shown that the results of ABOi transplants were comparable to those of standard-risk transplants.
-Techniques for ABO desensitization, as well as other procedures, are employed:
Remove circulating ABO antibodies: Plasmapheresis (PP) is a more affordable and straightforward method of removing circulating ABO antibodies; but, it is less successful; it removes only 20 per cent of antibodies each session, as well as protective antibodies and coagulation factors.
Double filtration PP is safer than single filtration PP because it allows for the return of smaller molecules to the patient. Immunomodulation: A high dosage of IVIG is used to replenish immunoglobulins that have been lost via the use of apheresis procedures, as well as for its immunoregulatory effects, which are intended to reduce antibody rebound and the risk of AMR.
B cell depletion: Splenectomy has been substituted with rituximab in order to achieve B cell depletion and reduce agglutinin titer to a preset level.
The protocols that are being employed are a combination of such tactics, with many efforts being made to lessen the difficulties and costs connected with them.
Clinical consequences include:
Transplant studies with ABOi patients are often conducted with small numbers of participants.
-Overall, transplants involving ABOi were associated with considerably higher death rates at 1, 3, and 5 years as compared to transplants involving ABOc. The increased death rate is most likely a result of the high level of immunosuppression associated with the treatment. Indeed, several trials in which chosen individuals got a lower dose of customized desensitization treatment showed an increased survival rate, with fewer infections and no evidence of atypical bacterial meningitis.
-Surgical complications in ABOi transplantations are comparable to those seen in normal transplants, ABMR is the most common cause of graft loss in ABOi transplantations, accounting for almost half of all graft losses.
-KPD, 2 pairs of donors and recipients with ABOi exchange kidneys; the number of pairings may be increased to encompass a greater number of donors and recipients.
-KPD is less expensive, however, it may be linked with a longer waiting period.
The costs of KPD are comparable to those of ABOc kidney transplants.
Although renal transplantation is considered the best therapy for patients affected by end-stage renal disease , however , approximately 30% of such transplantations are considered incompatible from the immunological point of view either because of the presence in the recipient of antibodies directed against the human leukocyte antigen (HLA) antigens of the donor or because of the incompatibility of the ABO system between the donor and recipient or because of both .
IMMUNOLOGICAL ASPECTS
The antigens of the ABO system are glycoproteins expressed on erythrocyte membranes as well as on epithelial and endothelial cells. At the renal level, these glycoproteins are also expressed on the collecting and distal tubules and on the vascular endothelial cells
The reaction of isoagglutinins with the antigens of the ABO group induces complement activation, as documented by the presence of C4d
having both types of Ab ( Anti A & Anti B ) , recipients of blood type O have a higher incidence of antibody-mediated rejection (ABMR) after transplantation
In a graft from a donor with blood group type A of the A2 subtype , the A2 Ag is less expressed on tissues and thence confers less immunogenic risk .4
DEVELOPMENT OF THE PRACTICE OF KIDNEY TRANSPLANTATION IN
ABO- INCOMPATIBLE PAIRS
For a long time, ABOi has been considered an absolute contraindication to kidney
transplantation but with the evolving desensitization protocols it has become increasinglyy adopted with good outcomes
TECHNIQUES OF ABO DESENSITIZATION AND DIFFERENT PROTOCOLS
USED OVER TIME
The most frequent protocols applied to obtain desensitization in pairs with ABOi are a
mixture of the following strategies.:
Removal of circulating ABO antibodies
The removal of circulating ABO antibodies is obtained principally by plasmapheresis
or immune-adsorption (IA). The aim of these strategies, principally applied several
days before transplantation, is to reduce the circulating anti-A/B antibody levels to
achieve titers between 1:8 and 1:32.
the apheretic techniques is the principle of desensitization and carried out by different ways :
1)The simpler, cheaper, but less effective technique has been the therapeutic plasma
exchange using highly permeable membranes. The procedure eliminates
approximately 20% of the antibodies by session. Additionally, removes protective
antibodies and coagulation factors.
2)The double filtration plasmapheresis is performed by two plasma filters, and the
second one allows smaller molecules to return back to the patient, avoiding many
complications associated with the therapeutic plasma exchange.
3)further evolution has been made by the use of columns for the selective removal
of humoral factors by Immunoadsorption IA .
Immunomodulation
This technique consists in the administration of high doses of polyclonal intravenous
immunoglobulin (IVIG) to the patient before transplantation. The aim is to replace the
patient’s immunoglobulins lost because of apheresis techniques. In addition, IVIG
blocks the Fc receptor and has immunoregulatory properties
B cell depletion
Being the producers of iosagglutinins , B cell depletion is essential to have effective desensitization . Historically it was achieved with splenectomy but the use of Anti CD 20 Rituximab has largely replaced splenectomy and is almost abandoned nowadays .
CLINICAL OUTCOMES AFTER RENAL TRANSPLANTATION INVOLVING
ABOI
The results obtained after renal transplantation involving ABOi and reported in this
review are generally good and overlap with the results obtained in ABOc renal
transplantation.
The main limitation of the review is the lack of randomized controlled trials. As a consequence, the systematic review does not allow us to compare the different therapies. The review only highlights the possibility that RTX and IA could have a superior efficacy, although this point remains to be confirmed by randomized controlled trial .
studies conducted on ABOi KT patients evaluated pateint and graft survival according to the preconditioning therapy
. Overall, transplants involving ABOi compared to those involving ABOc had a significantly higher mortality rates at 1, 3 and 5 years (odds ratio 2.17, 1.89 and 1.47, respectively; P < 0.0001). Both graft losses and mortality in transplants involving ABOi became equivalent to ABOc transplants at 8 years after transplantation.
The higher mortality rate is probably a consequence of the high immunosuppression related to the therapy which is leading cause for severe bacterial or viral infections , in this regard ,Polyoma virus nephropathy was also more frequent in patients receiving RTX
Coagulation disorders were also frequent in transplant involving ABOi. This complication is probably related to the modifications in the coagulation system induced by plasmapheresis or IA
OPEN CONTROVERSIES IN KIDNEY TRANSPLANTATION INVOLVING
ABOI
The different and discordant results reported by the different authors highlight the
controversies that are still open in kidney transplantation involving ABOi. The vast
majority of controversies concern the strategies of desensitization , The most common controversies are the following :
1.Apheresis technique used
Although specific IA is superior to others but still it is costy and not widely available
2.Role of rituximab
The use of RTX reduces the risk of isoagglutin rebound and the risk of ABMR. In
addition, the risk of chronic rejection seems to be reduced by the use of RTX
3.Utility and role of IVIG
In transplants involving ABOi, the IVIG administration reduces the antibody
rebound after transplantation and the risk of ABMR
4.Method to detect isoagglutinins quantity
To decide on the immunosuppression and in particular the apheresis technique to be
used, it is necessary to know the isoagglutinin titer.
The best method is flux cytometry, even if the method has a high cost. The tube
and gel techniques are also frequently used
5.Type of immunosuppression
Apart from desensitization, the immunosuppression in kidney transplantation with
ABOi is similar to that used for standard transplantation. The basal immunosuppression begins together with the desensitization.
6.Utility of posttransplantation apheresis
Apheresis treatments post-transplantation are reserved for patients who present
abnormalities of graft function together with isoagglutinin rebound
7.Accommodation
Accommodation in renal transplantation involving ABOi has been defined as the
presence of circulating isoagglutinins and antigens on the graft cells with normal renal
function and normal histology , this is usually gained with good desensitization and Ab depletion
8.Role of protocol biopsies
Here it is worthy to know that the presence and the role on protocol biopsies of C4d in
transplantations involving ABOi seems to be related to accommodation when found in
the absence of clinical or other histological abnormalities.
9.Principal complications
#surgical hemorrhage is more due to the coagulation factors loss in aphresis therapy that is also proportional to the No. of sessions
#intensified immunosuppression and the resulting infections
# ABMR is the first cause of graft loss in transplantations involving ABOi. The risk
for ABMR is related to the isoagglutinin level at transplantation and to the presence of Anti HLA Abs
KPD
It is an option to overcome the immunologic barriers without desessitization .
its simplest model is the two-way , With the increasing number of KPD programs, it has been possible to achieve a
global kidney exchange. Starting from a single-center experience, a state wise
experience was realized followed by a national program and an international
program .
MAKING A CHOICE BETWEEN DESENSITIZATION AND KPD
An answer to this question is difficult to be given. Indeed, given the fact that KPD is
generally cheaper with respect to desensitization, it remains to be answered the
availability of KPD in a short time.
Introduction: Both the ABO I and HLA I kidney transplant account for 30% of the living donor kidney transplant, By history the ABOI KT was considered absolute contraindication for kidney transplantation due to hyper acute rejection and graft loss . The main two approaches to overcome this problem are by using different desensitization protocol to target antibodies removal pre-transplant and prevent the ABS rebound after transplantation or by using the kidney exchange program. This review article focuses on reviewing the most recent evidence from the literature of the different desensitization protocols and ABO I kt clinical outcome. Also highlight the improvement of the different techniques of desensitization overtime including the use of more selective and specific type of apheresis for selective ABS removal with less side effects like moving from plasmapheresis to immunoadsorption (IA)Techniques with lower risk of infection and coagulopathy also moving from surgical B cell depletion by splenectomy which have been replaced nowadays by rituximab anticd20 monoclonal agent additionally with the improvement in our Knowledge about the immune system and the use of molecular assays for monitoring this help to adopt the strategies to personalized the immunosuppression protocols to avoid intense immunosuppression and reduce the risk of infection, malignancy, overall kidney transplantation from ABOI living donors nowadays consider a safe and effective approach that help in increase the donor pool and reduce the waiting list with overall similar outcome compared to ABOc kidney transplantation.
DEVELOPMENT OF THE PRACTICE OF KIDNEY TRANSPLANTATION INABO- INCOMPATIBLE PAIRS
The use of ABOI kidney transplant increased in numbers worldwide with good outcome , A2 donor blood group to O recipient Kidney transplant shows very promising results Different techniques have been used as part of desensitization protocol and by principle no consensus about the best protocol and should be individuated case by case Usually using combination therapies
Therapeutic plasmapheresis in the range of 3-5 sessions targeting the antibodies removal by 20% , its cheap, available and less cost while the introduction of IA techniques is preferable more selective and specific for removal of anti A/B antibodies from the circulation with target titer < 1-16 or, 1.36 and associated with lower risk of complement activation less coagulopathy or infection but rather more cost.
IVIG act as immunomodulating agent, replace the Ig lost during plasmapheresis, block the FC receptors in activate T and B cells and enhance B cells apoptosis, different dosing, low or high dose after each session of plasmapheresis and additional dose at day of induction of 0.5gm/kg .
B Cell depletion was very important part of any desensitization protocol, as the B Cell responsible for production of isoagglutinin’s .Historically surgical B Cell deleting by splenectomy which was used as part of desensitization from old Japanese protocol and now replaced by rituximab anti -CD20 humanized monoclonal Abs single dose usually given 3- 4 weeks prior to transplantation date with very good results from many observational studies.
Trials address the further modification of desensitization protocol by adopting on demand strategies based on the isoagglutinin titer level and they individualized the desensitization protocol to avoid intense immunosuppression with its associated morbid complications, this on demand protocol target the use of less IA sessions and low dose rituximab of 200mg/m2 or rituximab alone based on the isoagglutinin titer with favorable outcome with less side effects and cost and comparable outcome to ABOc KTX with 1, 3 year follow-up . Isoagglutinin titer quantification by using different techniques with no standardized values and it consider of low predictive value for ABMR. However, the best assay by using flux cytometry.
Plasmapheresis indication after transplantation only when there is clinical evidence of graft dysfunction with increasing antibodies titer post transplantation
Accommodation:
referred to the state of stable graft function with no evidence of graft injury in the presence of low isoagglutinin titer with affinity and positive C4D staining in PTCS by protocol biopsies.
Complication of desensitization:
1- post-surgical bleeding which is more related with the numbers of the plasma therapy or IAs sessions.
2-Infections including bacterial and viral infection
3- ABMR, in the range of 10-30%, depend on the baseline isoagglutinin titer and the presence of anti HLA Abs.
Kidney pair exchange program :
The national or international KPD program have been increased since many years with expanding the chains from close chain to open loop with NDD or bridge donor in domino chain that help the access for better matched LD with less cost and shorting waiting list. but its application associated with many logistics including the availability of KPD in short time , donor travel and cost , closed vs opened chain
however currently access to KPD increasing compared to desensitization
Current protocols and outcomes of ABO-incompatible kidney transplantation
One of the most challenges in living renal transplantation is that a significant percentage are immunologically incompatible either because of the presence HLA antibodies directed against the HLA system of the donor or because of the incompatibility of the ABO system.
There are Two different strategies to overcome these barriers: first is desensitization of the recipient to remove the antibodies either against HLA antigens or iABO antibodies and to prevent their rebound after transplantation and the second option is exchange of organs between two or more pairs what is called paired kidney exchange.
The number of renal transplantations between ABO-incompatible pairs have been increased because of improved knowledge of the immune system and the availability of new drugs. Rituximab has substantially replaced splenectomy. Also, the technique of plasmapheresis eliminates the preformed alloantibodies, and high-dose intravenous immunoglobulins improve the immunomodulation. Recent reports document that the outcomes for iABO transplantation similar to the outcomes of standard transplantation.
The ABO antigens are glycoproteins expressed on erythrocyte membranes as well as on epithelial and endothelial cells. In the kidney, these glycoproteins are expressed on the collecting and distal tubules and on the vascular endothelial cells. The reaction of isoagglutinins with the antigens of the ABO group induces ABMR through complement activation, as documented by the presence of C4d as well as causing chronic ABMR.
TECHNIQUES OF ABO DESENSITIZATION AND DIFFERENT PROTOCOLS USED OVER TIME
1-Removal of circulating ABO antibodies which done by plasmapheresis or immune-adsorption,the aim of this procedure is to reduce the circulating anti-A/B antibody levels to achieve titers between 1:8 and 1:32. The double filtration plasmapheresis is performed by two plasma filters, and the second one allows smaller molecules to return back to the patient.
2-Immunomodulation :This includes administration of high doses of IVIG to the patient before transplantation. The aim is to replace the patient’s immunoglobulins lost with plasmapheresis . As well as IVIG blocks the Fc receptor and has immunoregulatory properties.
3-B cell depletion: Historically, splenectomy has been used principally in Japan for B cell depletion. Nowadays RTX, the anti CD20 expressed on the B cell membrane, is the drug used to for B cell depletion. The aim for B cell depletion is to reduce the isoagglutinin titer to accepted levels.
When the transplanted kidney exposed to a low ABO antibody titer, In 2 weeks it has the capacity to resist complement-mediated damage and develop form of accommodation.
CLINICAL OUTCOMES AFTER RENAL TRANSPLANTATION INVOLVING ABOI
The short and medium outcomes results obtained after ABOI renal transplantation reported in this review are generally good and overlap with the results obtained in ABOc renal transplantation. But the results reported obtained from studies with small number of patients.
Overall, transplants involving ABOi compared to those involving ABOc had a significantly higher mortality rates at 1, 3 and 5 years. Both graft losses and mortality in transplants involving ABOi became equivalent to ABOc transplants at 8 years after transplantation.
The higher mortality rate can be explained by infectious complications secondary to high immunosuppression therapy. Excess immunosuppression is the cause of severe bacterial or viral infections. Coagulation disorders were also a frequent complication is probably related to the modifications in the coagulation system induced by plasmapheresis or IA.
some studies in selected patients who received a lower, tailored desensitization therapy reported an improved survival rate, with fewer infections and without ABMR.
ABOi transplant previously considered a contraindication now is a possibility with 30%increase in tx rate due to dire need of organs.
ABO ag is an oligosaccharide Ag which is present on rbc,glomerulus,tubules, endothelium which reacts with anti-A and B titre that will cause early rejection.So the sole purpose of desensitization is reduction of ab titre to a safe limit of B>A2 in line of immunogenicity.
Here the main culprits are-
1.Antibody(IgG is imp than IgM,because IgM is intravascular hence amenable to removal)
2.B-cell/plasma cell
3.complement
Mode of removal/suppression-
1.ANTIBODY
A.plasmapheresis(nonspecific,albumin,coagulation proteins also removed along with20%reduction in Ab)
B.double filtration plasmapheresis(more specific,only albumin loss)
C.immuneadsorption(specific IA against anti-A or anti-B)(no loss of albumin)
2.B-CELL
A.splenectomy (not practised now)
B.Rituximab (low to high dose, replaced splenectomy with increase in death censored graft function and prevent rebound of ab titre during initial tx weeks)
3.COMPLEMENT-
A.eculizumab (very expensive)
B.IVIG-modulate the immunity by neutralization of antibody,complement,T-cell inhibition,supplement immunoglobulin deficiency, but increases antibody titre)
4.ATG/BASILIXIMAB induction with triple immunosuppression.
5.TAILORED DESENSITIZATION-
titre 8-only rtx
titre 16-64-plasmapheresis+rtx
titre >64-IA+RTX
OUTCOME-patient survival is less due to more infections,mdr bacteria colonization,bkvirus nephropathy, but malignancy risk is equal.
ABOi tx graft survival,patient survival ,death censored graft survival is equivalent to ABOc tx but initial survival is less due to increased infections and rejection.
MAIN CONTROVERSIES IN ABOi TX
A.Technique of apheresis-not standardized
B.Role of rtx-should be given 1mnth early as it’s action starts between 3wk to 6mnth, and should be in lower dose and avoided just before tpe.
C.ivig-dose not standardized, as commonly used 500mg/kg before tx.
D.isoagglutinin quantification-not standardized, but flowcytometry is best,with gel method preferred over tube method.
E.immunosuppression-steroid withdrawl should be avoided
F.post tx apheresis-should be performed post tx graft dysfunction with rebound of titre.
G.Accomodation-mainly due to low titre of antibody,complement deactivation, with phenotypic endothelial changes.
H.role of protocol biopsy-not so informative.
So concluding that desensitization should always be avoided in place of availability of kidney paired donation, but TIME ⏲️ plays the deciding role here.
· Blood group antigens are presented on RBCS , endothelial cells and renal tubular epithelial cells in certain circumstances, they include A, B, AB, O
· Patient with blood group A has anti B antibodies, while those with blood group B has anti -B antibodies.
· Individuals with blood group O has no antibodies so they are universal donors. However, patients with blood group AB are universal recipient.
· Blood group A has 2 subtypes: A1 (80 %) and A2 (20%, and less immunogenic).
Desensitization protocol
v B cell depletion
v Antibodies removal
v IVIG
v Immunosuppression;
v Monitoring
Outcome
Disadvantages of ABO i transplant:
ABO incompatible are now possible for renal transplant and expensive due to desensitisation protocol, However is less costly in comparison to patients staying on dialysis.
This article focus on strategies of desensitisation protocol and choice between the PKD and desensitisation protocol.
ABOi results from glycoproteins expressed on surface of RBC and surface of many endothelial cells and epithelial cells especially collecting ducts and distal renal tubules. It’s responsible for hyperacute rejection and ABMR lead to activation of complement and graft loss. this high titer of anti A/B antibodies can removed by plasma exchange before and after transplant but double filtration plasma pharesis less complications because second filter lead to return small molecule to blood.
Selective immunoadsorption more benefit than non selective immunoadsorption in removal of IgG class and remove isoagglutinins.
Another step in desensitisation protocol is immunomodulation with high dose of intravenous immunoglobulin post plasma session to replenish immunoglobulin lost by plasma exchange.
B cell depletion by rituximab 375mg/m2 anti CD20 monoclonal antibody against B cell which replaced by Japanese in 2005 instead of splenectomy.
By this method graft survival smilar to ABOC but survival patients less due to infection because intensity of immunosuppressive drug.
Inhibition of complement activation by C5 inhibitors Eculizumab.
Maintenance therapy with triple immunosuppressive agents MMF and Calcinurine inhibitors and low dose steroid. there’s may history of rejection after withdrawal steroid in patients with ABOI.
There’s risk from surgical complications and coagulation disorder post plasma exchange and high risk of infection in those patients.
Serial graft biopsy at 3m and 12m to avoid ABMR. But most of them have accommodations phenomena presence of C4d deposition along peritubular capillarities and low titer of antibodies without evidence of graft rejection. Despite this improvement in ABOI transplant but declined in recent months due to development of PKD program from living donor compatible which are less expensive and less complications especially infection.
However there’s many issues of PKD program should be clarified regarding:
– [ ] kidney or donor travel
kidney travel less expensive than donor
– [ ] simulations and non simulation issues
– [ ] close chain versus open chain
Conclusion
PKD more safe than ABOI transplant because less expensive and less hazardous of infectious and non infectious complications.
· Summarise this article
ABO incompatibility hampers 30% of living donors from donating a kidney. ABO system antigens are glycoproteins on RBCs, vascular endothelial cells, collecting and distal tubules. AMR occurs due to membrane linked antigens as well as free circulating epitopes A and B. The isoagglutinins react with ABO group antigens, activating complement, giving a positive C4d stain.
There are 2 ways to overcome ABO incompatibility: either ABO incompatible transplants after desensitization, or a paired exchange transplant.
The techniques for ABO desensitization include:
1) Removal of circulating ABO antibodies: Either of the following methods can be used.
a.Therapeutic plasma exchange (TPE) using highly permeable membrane: A session decreases 20% antibodies, but also causes loss of protective antibodies and coagulation factors.
b. Double filtration plasmapheresis (DFPP): It prevents loss of smaller molecules, reducing the complication with TPE.
c. Immunoadsorption (IA) with immobilized antibodies: Most widely used, include columns containing polyclonal sheep anti-human IgG antibodies, or staphylococcal protein A.
2) Immunomodulation using IVIG: To replace the immunoglobulins lost and block Fc receptors as well as inhibit complement activation and circulating anti-HLA antibodies, reducing rebound and AMR.
3) B cell depletion: History splenectomy was done for B cell depletion, which has now been replaced by anti-CCD20 rituximab use which decreases tire rebound, chronic rejection and AMR rates.
The aim for desensitization is to reduce the isoagglutinin titres to a predetermined level prior to transplant, irrespective of the protocol used. The common features of all protocols include use of triple drug immunosuppression (in form of Tacrolimus, MMF and steroids), Plasmapheresis or immunoadsorption, IVIG with or without rituximab.
Various protocols used include:
1) Genberg et al: Rituximab 375 mg/m2 30 days before transplant, IA and IVIG 500mg/kg a day before transplant.
2) Japanese researchers: Rituximab replaced splenectomy after 2005.
3) Barnett et al: Tailored desensitization strategy according to isoagglutinin titres. <8: none, 8: rituximab, 16-64: rituximab with plasmapheresis, >64: rituximab with immunoadsorption.
To look for the outcomes of ABO incompatible transplants, 2 meta-analysis have been published.
Meta-analysis by Lo et al, although lacked randomized controlled trials, highlighted the possibility that rituximab with immunoadsorption might have a superior effect with fewer side effects with the evidence being of low level.
Another meta-analysis revealed higher mortality rates with ABO incompatible transplants at 1,3 and 5 years (consequent to increased infection due to higher immunosuppression, especially with rituximab use showing increased polyoma virus nephropathy) with equivalent graft and patient survival at 8 years. These findings emphasize the importance of a tailored approach for immunosuppression to decrease infections, mortality and AMR rates.
There are still some challenges in ABO incompatible transplants:
1) Controversy regarding method of apheresis: Different centres use different techniques with no consensus on best form of apheresis. IA have fewer side effects but higher costs.
2) Role of rituximab: Some centres do not use rituximab and have results similar to ABO compatible transplants.
3) Role and dose of IVIG: Some centres use 100 mg/kg after each plasmapheresis, some use 500 mg/kg one day prior to transplant, while others divide the dose in 2 sessions 4 day and 1 day prior to transplant.
4) Technique of isoagglutinin quantification: Flux cytometry is best but costly. Tube method and gel methods are more widely used. Although the basal titre pre-transplant and post-transplant titres have low predictive value for AMR.
5) Immunosuppression protocols: Steroid withdrawal shows poor results, hence not recommended.
6) Role of post-transplant apheresis: Only to be done if graft dysfunction with rising isoagglutinin titres, not on the basis of titre alone.
7) Role of protocol biopsies: It seems there is no role of protocol biopsies as far as ABO incompatible transplants are concerned.
8) Complications: Surgical complications, except for haemorrhages, are similar to ABO compatible transplants. Risk of AMR is high in first 2 weeks post-transplant, and is related to isoagglutinin titres at transplant and anti-HLA antibodies.
Kidney paired donation (KPD) is another way of transplanting ABO incompatible pairs but has certain unresolved issues like transporting kidneys versus transporting donors, simultaneous or non-simultaneous transplants and use of closed chains versus open chains. KPD is cheaper and more immunologically sound process and it should be encouraged as much as possible. ABO incompatible transplants can be offered after exhausting other avenues, but should be offered (with tailored approach) rather than keep waiting for a deceased donor.
Current protocols and outcomes of ABO-incompatible kidney transplantation.
INTRODUCTION:
Transplantation is the best modality of ESRD and pre-emptive LRKTX has the best outcome but there is an obstacle which is approximately 30% of such transplantations are considered incompatible from the immunological point of view due to (HLA or ABO incompatibility).
So to overcome this situation we can desensitize our patients with new protocol combined with Paired Kidney Donation.
IMMUNOLOGICAL ASPECTS :
These oligosaccharides are expressed on the surface of a variety of different cell types, including RBCs, endothelial cells and kidney parenchymal cells.
Antigenic expression of A2 is quantitatively and qualitatively less than that of A1, immunogenic risk based on antigen expression alone is A1>B>A2.
The A2 subtype does not have circulating antigens linked to von Willebrand factor.
Better results in transplantation involving ABOi are obtained when transplanting kidneys from A2 donors to O recipients.
TECHNIQUES OF ABO DESENSITIZATION AND DIFFERENT PROTOCOLS USED OVER TIME:
A- Removal of circulating ABO antibodies.
PEX or IA to reduce the circulating anti-A/B antibody levels to achieve titers between 1:8 and 1:32.
PEX remove 20% of the antibodies by session, each option has its merits and demerits.
The double filtration plasmapheresis is performed by two plasma filters, and the second one allows smaller molecules to return back to the patient.
B- Immunomodulation:
Intravenous immunoglobulin (IVIG) to the patient before transplantation aim is to replace the patient’s immunoglobulins lost because of apheresis techniques.
C- B cell depletion:
Anti-CD 20 Rituximab now is considered medical splenectomy.
For B-cell depletion is used now by rituximab in most protocols.
Also some protocols not used rituximab at all if patient had reached an anti-A/B antibody titer of less than 1:32 with good graft survival.
The Guy’s Hospital, Barnett et al adopted their strategy according to the initial anti-ABO antibody titer . With a titer of 8, only RTX was used; with a titer between 16 and 64, plasmapheresis was added to RTX therapy; and with a titer > 64, IA and RTX were used. In total, 62 kidney transplants involving ABOi were performed using this strategy compared with 167 ABOc transplants. Showed that no difference was observed between the two groups in allograft and patient survival rates at 1 and 3 years or in the ABMR rates .
CLINICAL OUTCOMES AFTER RENAL TRANSPLANTATION INVOLVING ABOI
systematic review gives different results . This review examines 7098 renal transplantations involving ABOi shown that Overall, transplants involving ABOi compared to those involving ABOc had a significantly higher mortality rates at 1, 3 and 5 years which mainly due to higher mortality rate due to infectious disease or side effects of high immunosuppression.
Both graft losses and mortality in transplants involving ABOi became equivalent to ABOc transplants at 8 years after transplantation.
OPEN CONTROVERSIES IN KIDNEY TRANSPLANTATION INVOLVING ABOI
Apheresis technique used:
Specific columns used for IA are more efficient with fewer side effects than nonspecific columns but costly and number depend on center protocol and titer of antibodies.
Patient with low titer still there is controversy about needing apheresis or not.
Role of rituximab:
The use of RTX reduces the risk of isoagglutin rebound and the risk of ABMR but removed by PEX.
Utility and role of IVIG:
IVIG administration reduces the antibody rebound after transplantation and the risk of ABMR may be used one day before TX or with PEX.
Method to detect isoagglutinins quantity
flux cytometry is the best even if the method has a high cost. The tube and gel techniques also used.
Type of immunosuppression
The basal immunosuppression begins together with the desensitization but steroid withdrawal has high incidence of rejection.
Utility of post-transplantation apheresis
With rebound and graft dysfunction.
Accommodation
Accommodation :the presence of circulating isoagglutinins and antigens on the graft cells with normal renal function and normal histology with or without of C4d.
Principal complications:
ABMR is the first cause of graft loss in transplantations involving ABOi
Some bleeding which reflect mainly effect of PEX or IA.
KPD:
Base on a single center strategy, on a regional strategy on a national or international strategy. Cheaper than desensitization.
Decrease time on waiting list and provide good compatible donor.
CONCLUSION:
Overall ABOi kidney transplantation has many benefits and allow many chances for Recipients on waiting list specially with PKD.
With good graft and patients survival.
But still no randomized control trial to ensure or prefer one protocol over others.
Need more clinical trials specially with low immunosuppressive protocols and desensitization to avoid infections and malignancy.
Kidney transplantation is the treatment of choice for patients with end stage renal disease.
Sensitized patients and patient with ABOi pairs wait for long time to get appropriate kidney offer.
Two major strategies evolved to overcome the immunological risk.
1- Paired kidney exchange program
2- Desensitization and transplantation against ABO system.
Overview of desensitization — The overall goals and purpose of ABO desensitization are to lower the immunogenicity of the incompatibility to allow for successful transplantation with commonly used induction and maintenance immunosuppressive regimens. Although there is no uniformly accepted ABO desensitization protocol, most commonly used protocols employ a combination of the following strategies:
●Removal of circulating ABO antibodies, typically with extracorporeal methods such as plasmapheresis or immunoadsorption
●Immunomodulation of the recipient immune system, typically with intravenous immune globulins
●Depletion of the B cell population responsible for ABO antibody production, most commonly with the anti-CD20 agent rituximab
Removal of circulating ABO antibodies – The two most commonly used methods of antibody removal are plasmapheresis and immunoadsorption, with the goal of achieving titers ≤1:8 to 1:32.
Immunomodulation — IVIG is to replace immunoglobulins that are removed with plasmapheresis or immunoadsorption. In addition, IVIG may also block Fc receptors to prevent a rebound in anti-A/B antibody titers when the plasma cells have naked receptors and, therefore, are stimulated to make more antibody.
B cell depletion —Rituximab, a humanized mouse monoclonal antibody that targets CD20 (expressed on the majority of B cells), is the most commonly used agent. Splenectomy, which was historically used for this purpose, is no longer used in most countries. Despite an absence of detectable splenic B cells after rituximab administration, plasma cells remain as the majority of plasma cells lack CD20 receptors. The specific dose of rituximab required in this setting is unclear. Rituximab is given four weeks prior to the scheduled transplant surgery date.
Immunosuppression Apart from desensitization, the immunosuppression in kidney transplantation with ABOi is similar to that used for standard transplantation which includes CNI based triple therapy namely TAC/MMF/PRED.
Post-transplantation apheresis Apheresis treatments post-transplantation are reserved for patients who present abnormalities of graft function together with isoagglutinin rebound. Antibody rebound is expected in 2 weeks following transplantation, and not associated with histological signs of AMR.
Accommodation-Accommodation in renal transplantation involving ABOi has been defined as the presence of circulating isoagglutinins and antigens on the graft cells with normal renal function and normal histology.
Role of protocol biopsies
The presence and the role on protocol biopsies of C4d in transplantations involving ABOi seems to be related to accommodation when found in the absence of clinical or other histological abnormalities.
In conclusion, ABOi renal transplantation is evolving because of the reconditioning strategies available and good outcomes comparable to the ABOc transplants on the long term followup.
TECHNIQUES OF ABO DESENSITIZATION ,
IV. Current protocols and outcomes of ABO-i incompatible kidney transplantation
Summarise this article
Introduction
The use of ABO- renal transplantation is increasing in this century with the increase in our knowledge of the immunological barriers & the advent of new drugs.
The main historical steps in the evolution of desensitization are:
1. 2004:
Takahashi et al
IA or PP 2-3 times before transplantation
Splenectomy
441 transplants
2. 2005:
Gloor et al
PP,IVIG & anti-CD20 before transplantation
No splenctomy
11 transplants
3. Genberg et al
IA & anti-CD20 before transplantation
LMW heparin
No splenectomy
15 transplants
Currently different combinations of the following are used in ABO-i transplantation:
1. IA or PP for removal of ABO antibodies.
Started day to weeks prior to transplantation to achieve an acceptable A/B titers (1:8 to 1:32)
The number of sessions for both PP & IA differ depending on the baseline antibody titer.
PP is simpler & cheaper than IA
It removes 20% of antibodies/session
S/E include removal of protective antibodies & coagulation factors leading to infections & hemorrhages.
Different techniques of IA allow more selective removal of antibodies & less side effects, though with extra costs.
===========================================
2. High dose of IVIG to replace immunoglobulins lost by PP or IA. Mostly given as single dose of 500 mg IVIG/kg BW on the day before transplantation. It can also be given in 2 divided doses -4 & -1 days before transplantation.
=========================================
3. Anti-CD20 Rituximab has largely replaced splenectomy for B cell depletion.
The dose is generally 375 mg/m2; its major effect is between 3 week & 6 months.
=========================================
4. Immunosuppression:
Similar to that used for standard transplantation.
Started together with the desensitization.
Reduction of immunosuppression is generally not
allowed in ABO-i transplants.
===============================================
Clinical outcomes:
Systemic reviews & meta-analyses show:
Significantly higher mortality rates at 1, 3 & 5 years in ABO-i vs ABO-c transplants.
Graft losses & mortality are equivalent in both groups at 8 years after transplantation.
The higher mortality rate is related to the intense of IS therapy.
PP & IA also induced more coagulation disorders in ABO-i. transplants.
Another way to overcome immunological barrier is enrolment of ABO-i recipients into PKD programs, or a combination of PKD & desensitization to reduce complications.
This review article describes different protocols and outcome of ABOi – KT.About 30 % patients awaiting a renal transplant are considered incompatible from immunological perspective because of Anti HLA antibodies of ABO incompatibility. There are two options to overcome these barriers:
1-Desesitization
To remove antibodies from recipient and modify immunological response so that transplantation can be made feasible
2- Paired kidney exchange
To exchange organs between two or more pairs to exchange between different donors.
Immunological aspects
ABO glycoproteins are expressed on RBC, endothelial cells and epithelial cells. in kidney these are expressed on Collecting and distil tubules and vascular endothelial cells. ABO blood group system has 4 categories including A,B,AB and O. Blood group O have high antibody titres against A and B. So recipients of blood group O have higher chances of ABMR. Circulating epitopes A and Blinked to VW factor when free can cause ABMR. In ABOi – KT better results are achieved when transplanting kidneys from A2 donors to O recipients.
Desensitization Protocols
Plasmaphresis (Pp) or immune adsorption
To remove circulating ABO antibodies . Target is to lower the antibody titres between 1:8 to 1:32.
Immuno Modulation-
IVIG replace the immunoglobulin lost during PP-It also blocks Fc receptors and causes immune regulation.
B ell depletion-
Using Rituximab- it blocks CD 20 receptors on plasma cells- Medical Splenectomy has now replaced surgical Splenectomy.
Accommodation-
This process decreases the risk of rejection by tolerance and low affinity of antibodies and by blockage of compliment activation
Immunosuppression will involve induction with either ATG or Basiliximab and maintenance with TAc, MMF and prednisolone. There is higher risk of AMR in ABOi – KT and its costly treatment . ABOi – KT can be complicated by infections and bleeding as clotting factors are lost in PP.
Out come of ABOi – KT
Outcomes in ABOi – KT at 1, 3 -5 years are low as compared to and ABOc -KT.
Significant increase in AMR in in ABOi – KT but not much increase in cell mediated rejection.
ABOi kidney transplantation and KPD are the 2 main strategies to overcome shortage of deceased donor organs and to allow patients with advanced age, cardiovascular disease and immune reactivity to avoid long waiting time on dialysis.
Immunological aspects:
ABO system antigens are expressed on RBCs, tubules and vascular endothelium.
Group O patients have higher anti-A/B antibody titer causing higher incidence of AMR post transplant while kidneys from A2 donors to O recipients show better results.
Development of the practice of kidney transplantation in ABOi pairs:
ABOi was a contraindication for kidney transplantation.
However, ABOi transplants increased worldwide due to
Techniques of ABO desensitization and different protocols used:
Removal of circulating ABO antibodies:
Plasmapheresis (PP) is cheaper, simpler but less effective, it removes 20% of antibodies per session with removal of protective antibodies and coagulation factors.
Double filtration PP is safer than PP as allow smaller molecules to return back to the patient.
IA selectively remove humoral factors with removing of ABO agglutinins.
Immunomodulation:
High dose of IVIG used to replace immunoglobulins lost with apheresis techniques in addition to its immunoregulatory effects to decrease antibody rebound and risk of AMR.
B cell depletion:
Now rituximab replaced splenectomy to obtain B cell depletion to decrease agglutinin titer to predetermined level.
Protocols used are mixture of those strategies with several attempts made to reduce associated complications and costs.
Clinical outcomes:
Studies involving ABOi transplants are generally with low number of patients.
A systemic review examined 83 studies highlighted the efficacy of rituximab and IA but was limited by absence of randomized controlled trials.
A more recent and wider systemic review showed that ABOi transplants have significantly higher mortality rates than ABOc transplants at 1,3 and 5 years, mostly due to intense immunosuppression causing severe infections.
Open controversies in ABOi kidney transplants:
Accommodation:
It is lack of rejection in presence of circulating ABO antibodies with normal kidney function and normal histology.
It is facilitated by reduction of isoagglutinin levels, blocking of complement activation and rituximab.
Role of protocol biopsies:
It may show C4d deposition and seems to be related to accommodation when present in absence of clinical and histological abnormalities.
Complications:
Hemorrhage is more common in ABOi transplants, significantly associated with number of IA sessions.
Infectious complications have different incidence in different studies mostly vary according to intensity of desensitization.
AMR, the main cause of graft loss, related to level of isoagglutinin level at transplantation and presence of anti-HLA antibodies.
KPD:
2 pairs of donor and recipient with ABOi exchange the kidneys and may include higher numbers of pairs.
Making a choice between desensitization and KPD
KPD is cheaper but may be associated with prolonged waiting time.
Costs of KPD is similar to ABOc kidney transplants
According to data from US, overall KPD is increasing while desensitization strategies are decreasing.
IMMUNOLOGICAL ASPECTS;
The ABO blood groups consist of four categories (A, B, AB and O). The formation of anti- blood group antibodies occurs against the antigens that are not native to the host. Group O individuals have higher antibody titers to both the A and B antigens.
The antigens of the ABO system are glycoproteins expressed on erythrocyte membranes as well as on epithelial and endothelial cells. In the kidney these glycoproteins are also expressed on the collecting and distal tubules and on the vascular endothelial cells.
In addition to the membrane-linked antigens, circulating epitopes A and B, both soluble and linked to von Willebrand factor exist in some patients. These antigens, when free, are responsible for ABMR .
The A2 subtype does not have circulating antigens linked to von Willebrand factor . Indeed, better results in transplantation involving ABOi are obtained when transplanting kidneys from A2 donors to O recipients.
TECHNIQUES OF ABO DESENSITIZATION AND DIFFERENT PROTOCOLS USED OVER TIME;
1-Removal of circulating ABO antibodies;
The removal of circulating ABO antibodies is obtained principally by plasmapheresis or immune-adsorption (IA).
Plasma exchange;
The simpler, cheaper, but less effective technique .The procedure eliminates approximately 20% of the antibodies by session. Additionally, removes protective antibodies and coagulation factors.
Immune-adsorption (IA).
Made by the use of columns for the selective removal of humoral factors by IA. There are different types of columns for IA . IA with immobilized antibodies: are the most widely used.
2-Immunomodulation;
This technique consists in the administration of high doses of polyclonal intravenous immunoglobulin (IVIG) to the patient before transplantation.The aim is to replace the patient’s immunoglobulins lost because of apheresis techniques. In addition, IVIG blocks the Fc receptor and has immunoregulatory properties.
3-B cell depletion;
To date, RTX, a humanized monoclonal antibody that binds to CD20 expressed on the B cell membrane, is the drug used to obtain B cell depletion.
CLINICAL OUTCOMES AFTER RENAL TRANSPLANTATION INVOLVING ABOI;
Overall, transplants involving ABOi compared to those involving ABOc had a significantly higher mortality rates at 1, 3 and 5 years. The higher mortality rate is probably a consequence of the high immunosuppression related to the therapy. Indeed, some studies in which selected patients received a lower, tailored desensitization therapy reported an improved survival rate, with fewer infections and without ABMR.
Complications;
1-Surgical complications in transplantations involving ABOi are similar to complications of standard transplants, with the exception of hemorrhages.
2-ABMR is the first cause of graft loss in transplantations involving ABOi.
KPD ;
The simplest model of the KPD is the two-way, in which two pairs of donors and recipients with ABOi exchange the kidneys, thereby resolving the incompatibility.
A variant of domino KPD is the Never Ending Altruistic chain,which allows a higher number of recipients to be transplanted by the use of bridge donors .
KPD programs have several points that yet need to be better clarified. The principals are as follows:
1-Transportation of kidneys vs donor travel:
The travel of the organ minimizes the costs and allows the continuity of donor care.
2- Simultaneous vs no simultaneous exchanges:
The drawback of simultaneous donations is logistical, principally if multiple organ donors will be operated on in the same center.
3-Closed chains vs open chains:
The channels of transplantations initiated by a non- directed donor may be extended but should end with donation to a recipient on the waiting list.
MAKING A CHOICE BETWEEN DESENSITIZATION AND KPD;
KPD is generally cheaper with respect to desensitization, it remains to be answered the availability of KPD in a short time.
The costs were obviously higher in the case of ABOi transplant and evaluated in $ 65080 per transplant episode vs $32039 per transplant episode for ABOc transplant.
Introduction
Renal transplantation is the best form in renal replacement in patients with ESRD. However many patients cannot be transplanted due organ donors shortages and there remain in the waiting list time or die. Another problem is ~30% of recipients are incompatible with their donors because of either HLA antibodies or ABO antibodies[1] Th two suggested solutions to cross these immunologic barriers are desensitization and paired kidney donation. This review provides overview of ABOi-KT, techniques of ABOi-KT and its outcomes.
Immunological Aspects
The ABO system antigens are glyco-proteins expressed on RBCS, as well as endothelial cell, tubuli,and glomeruli. Blood type O people have higher levels of anti A/B antibodies and therefore, they are at higher risk of AMR[3]. Better outcomes are seen when A2 donated to O patients. A2 doesn’t have circulating antigens linked to von Willebrand factor[5]
Development of practice of Kidney Transplantation in ABOi-pairs
Techniques of Desensitization and different protocols used over time
Removal of circulating ABO antibodies
Immuno-modulation
B cell depletion
B cell depletion facilitate accommodation ; the graft is resistance to injury in the presence anti A/B antibodies. This status is usually acquired after 2 weeks of transplantation even if the titer of anti A/B antibodies is high[21,22]
Clinical outcomes After ABOi-Tx
Open Conservatories in ABOi-rTX
PKD
Conclusion
Summary of Current protocols and outcomes of ABO-incompatible kidney transplantation
of this this review is describe the more recent data from literature on different protocol used and clinical out come of ABOi-KT .
30% of transplantation is incompatible.
Two ways to over come barrier for ABOi-KT :
1-desensitization to remove antibodies.
2-paired kidney donation between 2 paired or more..
IMMUNOLOGICAL ASPECTS
The antigens of the ABO system are glycoprotein expressed in RBCs ,epithelial and endothelial cells and kidney (tubules &vascular endothelial).
Presence of epitopes A&B both soul able and linked to von will brand factor existed in some patients these antigens where free are responsible fo ABMR.
Presence of c4d proof that there is reaction between antigens of the ABO group induce complement activation.
TECHNIQUES OF ABO DESENSITIZATION AND DIFFERENT PROTOCOLS USED OVER
There are different ways to achieve desensitisation with ABOi transplantation:
1-Removal of ABO antibodies and this through two method
Plasmapheresis
Immunoadsorption
Plasmapheresis simpler and cheaper but less effective and removal of protective antibodies and coagulation factors.
Immunoadsorption
1A2 different type
1-1A immobilized antibodies effective in removal IgG antibodies.
2-immoblized staphylococcal protein A removal of IgG with different classes.
2-Immunomodulation
High dose of polyclonal IVIG given to before patient before transplant aims to replace the patient immunoglobulin loss in apheresis technique .also blocks the FC receptor (immunoregulatory properties).
3-Bcell depletion
Rituximab humanized antibody bind to CD20 express on B cell membrane .
Is used to reduce agglutation titre level.
CLINICAL OUTCOMES AFTER RENAL TRANSPLANTATION INVOLVING ABOi
Wide systemic review end with different results
Overall ABOi -KT compared to ABOc had signific higher mortality rate at 1,3,and 5.
Graft loss and mortality in ABOi equivalent to ABOc -KT at 8year after Transplant.
Higher mortality rate related to high immunosuppression therapy cause sever viral and bacterial infection.
Coagulation disturbance induced by plasmapheresis or 1A.
Higher dose of rituximab result in infection such as polyoma virus nephropathy
Technique of apheresis
Column used for 1A
1- Specific column which is more efficient and fewer side effect.
2- Nonspecific less efficient and lower cost.
Numbers of apheresis treatment differ depend on level of
Isoagglutinin and the center.
Patient with low titre isoagglutinin plasmapheresis help in reduction of inflammatory molecules.
Role of RTX
Use of rituximab has allowed avoidance of splenectomy since 2002.
Use of RTX reduce the risk of isoagglutinin rebound and risk of ABMR and risk of chronic rejection.
Dose 375mg/m2 it major start 3 to 6 week after administration.
RTX begin 1 month before TX.
Avoid plasmapheresis after RTX(may be removed)
. IVIG
Mechanism of IVIG that modulate immune reaction are:
(1) Blockage of the Fc receptor on the leukocyte membrane.
(2) Inhibition of the complement activation.
(3) Inhibition of circulating antibodies against HLA.
Isoagglutinin quantificationhas
Flux cytometry s used to know isoagglutinin titre is high cost has low predictive value before desensitisation and postTX titre.
Immunosuppression
Immunosuppression in kidney transplant with ABOi is same as that used for standard TX.
Post-transplantation apheresis
Apply for patients with :
abnormal graft function with isoagglutinin rebound.
Accommodation
Is defined as presence of circulating isoagglutinin and antigens on the graft cells with normal renal function and normal histology..
Presence of low titre of antibodies with low affinity and with blockage of complement activation will explain accommodation.
Eculizumab may facilitate accommodation
. Complications
Bleeding related to number of apheresis treatment
Infection related to desensitisation
ABMR is first cause of graft loss in TX ABOi
KPD
KPD in the two ways in which 2 paired of donor and recipient with ABOi exchange the kidney so resolve incompatibility .
KPD can be national and an international program.
KPD programs have several points that yet need to be better clarified. The principals are as follows:
1-Transportation of kidneys vs donor travel.
2-Simultaneous vs no simultaneous exchanges.
3-Closed chains vs open chain.
CONCLUSION
ABOi barrier have been over come successful of ABOi KT refer to:
1- Accommodation.
2- Humoral tolerance.
3- desensitisation .
4- removal of isoagglutinin.
5- Immunoadsorption and antiCD20.
ABOi-KT more costive than ABOc-KT.
Presence of wide national registry in future will increase the number of transplantation.
.
Summarise this article :
1- desensitization with some variable protocols to remove antibodies and prevention of their rebound after transplantation.
2- paired kidney allocation by exchange of organs between 2 or more pairs. it is world-wide evolving but it has managed only 31% of pairs. however, this number can be increased if wide national registry would be used instead of smaller registries.
1- apharesis : it has been largely improved in recent years. however, several questions remain regarding the best techniques to be used.
2- IVIG : it acts by replacing the immunoglobulins lost with apharesis. also, it has immunoregulatory properties by blocking Fc receptors.
3- Immunoadsorption.
4- Rituximab : by blocking CD20 on plasma cells. it has replaced splenectomy.
1- accommodation : it means stable graft functions despite the presence of circulating antibodies and antigens on graft cell surface. presence of C4d on peritubular capillaries was added to the definition of accommodation on 2006.
2- humoral tolerance : it is an area on active research.
Transplantation is the treatment of choice for patients with ESRD, but shortage of deceased donor pool in addition to advance age, immunological activity or CVD are a big obstacles. So live donor a good alternative, but ~30 of patients on waiting list were sensitized. To overcome this there are 2 options:
ABO Ag expressed on RBC & on epithelial cells & endothelial cells. Blood group O Ag had the highest Ab titer against A & B Ag, so patient with blood group O had high risk of ABMR after ABOi-T. Circulated soluble epitopes of A & B Ag when be soluble can be linked to von-Willberand factor & cause ABMR, but A2 Ag didn’t have these soluble epitopes result in good result of ABOi-T.
ABOi-T became a good option for sensitized patients. Desensitization protocols involve combination of following techniques:
Combining of PP or IA with IVIG & rituximab show comparable result at 3 years between ABOi-T & ABOc-T.
Desensitization regimes are costly, so to reduce the cost :
The result of different studies show good result of both patient & graft outcome in ABOi-T, after 8 years post transplant, but there were increased mortality & BK virus infection in 1,3, & 5 years due to aggressive immunosuppression.
Multiple controversies of ABOi-T as:
It is difficult to decide which option is used for ABOi-T ( desensitization vs PKD ). Now Single center & regional exchange increase the facility of PKD with dropping of desensitization.
Transplantation of living donor is an option to avoid long term dialysis hazards but obstacles are faced including immunological barrier,which could be HLA and or ABO incompatibility , in order to solve this problem 2 strategies are applied which are desensitisation and paired kidney exchange program.
The most frequent protocols applied to obtain desensitization in pairs with ABOi are a combination of those strategies which are
Removal of circulating ABO antibodies
Using plasmapheresis or immune-adsorption (IA) and apharetic technique which is the most updated technique in order to lower the circulating anti-A/B antibody levels to reach titers between 1:8 and 1:32.
-plasma pheresis eliminates 20% of Ab in a session along with coagulation factors and protective Ab.
-double filtration plasmapheresis allows return of essential components to the blood there by avoiding PP drawbacks.
-IA selectively eliminates humoral factors using immobilised Ab or immobilised staph protein A or immobilized antigens and synthetic epitopes
Immunomodulation
Using IVIG having immunomodulatory role and replacing Ig lost in apheresis
B cell depletion
Using splenectomy which is currently replaced by Rituximab
Accommodation can occur protecting the kidney on the long term because by lowering ABO Ab titer graft can gain within 2 weeks a capacity to resist complement damage.
Genberg et al study mentioned that ABO incompitable transplant cases treated 30 days before transplantation with IA and Rituximab and IVIG one day before transplantation showed no significant difference between ABO compatible and incompatible groups regarding patient , graft survival and rejection.
Another study stated that stopping IA can cause rebound increase in Ab titer
The generally applied strategy is using Rituximab 10 days before Transplantation(Tx) and plasma pheresis /IA 1week before and after Tx along with 2 doses of IVIG prior Tx
Other policies used to lower Rituximab dose or decrease IA frequency with acceptable outcomes, concluding that individualising desensitisation has favourable net results.
Clinical outcomes after Renal Tx of ABOic cases
ABOi c Tx showed comparable outcomes to ABO c Tx but this was concluded from studies done on small number of cases
2 studies were done with bigger number of patients mentioned that Rituximab and IA have great efficacy but these studies had limitations.
More studies are needed to detect best protocols for cases with low pretransplant anti-ABO antibody titers
According to Anti A /B Ab titer desensitisation protocols are
If Ab titer <8—–induction and maintenance therapy
If 8 —-Rituximab— induction and maintenance therapy
If16-64—-Rituximab +DFPP—- induction and maintenance therapy
If>264—-Rituximab+IA—- induction and maintenance therapy
Mortality rate is higher in ABO ic Tx than ABO c Tx at 1,3 ,5 years could be due to extensive immunosuppression , coagulation disorders and infectious complications ,while graft loss and mortality is equal in both groups at 8 years post trasnplanation
Controversies in ABO ic Tx
Technique of apheresis
The high cost of specific columns used because it is efficient than other columns lead to reusage of those specific columns
It seemed that apharesis could be benefical even in cases with low Ab titers to decrease inflammatory molecules level
RTX role
It replaced splenectomy , it lowers the risk of isoagglutin rebound , the risk of ABMR and the risk of chronic rejection.
IVIG
It blocks FC receptor on leucocytes, inhibit complement activation and HLA Ab, also it decreases Ab rebound after Tx ,decreasing ABMR risk
Isoagglutinin quantification
Detected by flux cytometry , tube and gel technique .
On the other hand it has no predictive value for ABMR.
Immunosuppression
For ABO I cases is the same as for standard transplantation. It starts with the desensitization.
Post-transplantation apheresis
Is done for patients with abnormalities of graft function and with isoagglutinin rebound
Accommodation
Is the presence of circulating isoagglutinins and antigens on the graft cells with tolerance and less rejection risk due to due to the presence of a low titer of antibodies, with low affinity and with the blockage of complement activation.
Eculizumab can enhance accommodation.
Protocol biopsy role
C4d presence in grafts of ABOi Tx can be related to accommodation in the absence of clinical or other histological abnormalities
Complications
Surgical complications is the same for ABO incompatible and compatible Tx except hemorrhage is more common in ABO ic group due to aphaersis , number of IA done
Infection complication is dependent on desensitsation policy
ABMR risk varies according to the isoagglutinin level at transplantation and the presence of anti HLA
Kidney paired donation (KPD)
It includes 2 ,3 ,4 way and so on
Domino KPD allows a higher number of recipients to be transplanted by the use of bridge donors
Some issues are highlighted :
-transport of door versus the organ
-Simultaneous versus non simultaneous exchange
– Closed chains vs open chains
National Kidney Registry in the United States, revealed that KPD is increasing , while the desensitization strategy is decreasing
Blood group antigens are present not only in RBCS but also in the endothelial cells and they include A, B, AB, O
Patient with blood group A has antibodies against B antigen, while those with blood group B has anti -A antibodies
Individuals with blood group O has no antibodies so they are universal donors, on the other hand, patients with blood group AB are universal recipient.
Blood group A is subdivided into A1 and A2. A2 antigen is less common accounting for 20 % of white race individuals with blood group A, and is less expressed on RBCS than A1 so recipients with anti-A sera ( those with blood group B, O) can receive kidneys from donors with blood group A2 if anti-A sera is low. In other words individuals with blood group A2 can serve as universal donors but only if the titer of antibodies is low
Desensitization protocol
1– B cell depletion
2– Antibodies depletion
3– IVIG
Immunosuppression
Monitoring
Outcome
Complications
Cost
Transplantation from ABO incompatible donor became safe and available in order to increase donor pool and decrease waiting time to stay on dialysis and to shorten the waiting list of NDD and DCD.
ABO antigens are glycoproteins expressed on RBCs, epithelial and endothelial cells. They are 4 groups; A, B, AB, and O.
A group has A antigen and anti-B antibody, B group has B antigen and anti-A antibody, AB has A and B antigen and has no antibody, O group has no antigen and has anti-A and anti-B antibodies.
A group has two phenotypes A1 that is more antigenic and A2, which resemble O group, has no antigens.
In the renal system, ABO expressed on distal and collecting tubules and vascular endothelial cells, when expressed heavily, it is responsible for acute rejection attack.
The reaction of antibody or isoagglutinins with these glycoproteins will lead to complement activation and c4d deposition.
The first trial of transplantation from ABO incompatible donor was done in Japan.
TECHNIQUES OF ABO DESENSITIZATION AND DIFFERENT PROTOCOLS USED OVER TIME:
1- Removal of antibodies by apheresis ; plasma exchange with high permeable filter is less cost, available to remove antibodies by 20% every session, the main concern is its complications as it is non selective removes also clotting factors and other antibodies, so we can do plasmapheresis using double filter as the second filter allows the return of small important molecules try to avoid the complications, also we can use another adding filter or column to selectively IgG which is called immunoadsorption to avoid complications of removal of all antibodies.
2- Immunomodulation using IVIG post plasmapheresis session to replenish the removed beneficial antibodies.
3- Rituximab antiCD20 antibody, is medical splenectomy, it depletes B cells, which are responsible for antibody production.
There is no standard protocol for desensitization prior to transplantation, but in general, we can give rituximab 2 weeks prior to transplantation and do plasmapheresis 4 sessions 1 week before operation and continue it for another 3-4 sessions post transplant, tacrolimus ,MMF and steroid were given from 2-7 days prior to transplantation, keeping trough level of tacrolimus from 12-15 ng/ml.
CLINICAL OUTCOMES AFTER RENAL TRANSPLANTATION INVOLVING ABOI
Mortality in the patients transplanted from ABO incompatible donor is higher at 1, 3 and 5 years post-transplant than the patients transplanted from ABO compatible donor, this mostly related to side effects of heavy immunosuppression given to these patients like infections either bacterial and viral like BK virus, coagulation side effects.
Accommodation:
C4d deposition in absence of any signs and symptoms of AMR, so, this because of accommodation of the graft to that level of antibodies without making graft injury.
KPD program is another solution to enlarge donor pool versus transplantation from ABO incompatible donor, and the choice depends on many factors related to the center or hospital itself, availability and the cost.
Thank you Riham They mentioned giving Rituximab 2 weeks prior to transplantation, in fact, we give it in the UK 3 to 4 weeks prior to transplantation. Do you know Why?
B cell depletion takes 1-6 weeks to be completed, so given earlier
A. Nicholas R. Barnett, Vassilis G. Hadjianastassiou, Nizam Mamode. Rituximab in renal transplantation. Transplant International. 2013. 563–575.
The A2 subtype does not have circulating antigens linked to von Willebrand factor unlike other antigens, hence less risk of ABMR.
TECHNIQUES OF ABO DESENSITIZATION AND DIFFERENT PROTOCOLS USED OVER TIME
Removal of circulating ABO antibodies
Plasmapheresis-
eliminates approximately 20% of the antibodies by session. removes protective antibodies and coagulation factors.
double filtration plasmapheresis-
Avoids many complications associated with plasma exchange.
Immunoadsorption –
Therasorb column contains polyclonal sheep anti-human IgG antibodies .
Immunosorba columns, that contains staphylococcal protein A bound to sepharose.
immobilized antigens and synthetic epitopes.
These techniques are applied several days before transplantation, their aim is to reduce the circulating anti-A/B antibody levels to achieve titers between 1:8 and 1:32.
Immunomodulation –
administration of high doses of polyclonal intravenous
immunoglobulin (IVIG) to the patient before transplantation.
B cell depletion-
Initially splenectomy used to be done made popular by Japanese transplant program .
Rituximab replaced the need for splenectomy .
Scheme of desensitization treatment
Day -14 = rituximab
Day -10 = MMF
DAY -7 to +7= plasmapharesis/Immunoadsorption f/b IVIG.
Day 0 = tacrolimus + prednisolone
Guy’s Hospital, Barnett et al adopted a tailored desensitization strategy in pairs with ABOi.
titer of < 8= induction and maintenance therapy.
titer of 8 = only RTX
titer between 16 and 64= plasmapheresis was added to RTX
titer > 64 = IA and RTX were used.
With this tailored strategy no difference was observed between ABOi and ABOc groups in allograft and patient survival rates at 1 and 3 years or in the ABMR rates.
CLINICAL OUTCOMES AFTER RENAL TRANSPLANTATION INVOLVING ABOI.
Two systematic reviews and meta-analyses have been published.
review by Lo et al examined 83 studies,4810 kidney transplants involving ABOi were examined.
The main limitation of the review is the lack of randomized controlled trials.
Review showed that patients receiving the newest therapies have a better outcome with fewer severe side effects.
A more recent and wider systematic review gives different results and it examines 7098 renal transplantations involving ABOi.
Transplants involving ABOi compared to those involving ABOc had a significantly higher mortality rates at 1, 3 and 5 years .
Both graft losses and mortality in transplants involving ABOi became equivalent to ABOc transplants at 8 years after transplantation.
This higher mortality could be due to use of high immunosuppression leading to severe viral and bacterial infections and coagulation disorders induced by plasmapheresis and IA leading to bleeding risk.
OPEN CONTROVERSIES IN KIDNEY TRANSPLANTATION INVOLVING ABOI.
Technique of apheresis
Whether to use plasmapheresis which is cheap but leads to removal of all plasma proteins or IA which is 2-3 times costly but specific antibodies can be removed.
Also at what titer aphaeresis is needed is a question.
Role of RTX
As RTX may be removed by plasmapheresis, this technique should be avoided after RTX administration.
In the meta-analysis of ABOi transplants only 35% of patients were treated with RTX.So when and how much to give rituximab is the question.
IVIG
Some authors prefer to divide the IVIG dose 500mg /kg body weight and to administer IVIG in two different sessions 4 d and 1 d before transplantation.
Isoagglutinin quantification
Flow cytometry method is best but costly and not available at all centres.
Tube method
Gel method.
Immunosuppression
Whether steroid withdrawal is feasible is a question.
Post-transplantation apheresis
Whether to be done routinely or only in the case of issagglutinin rebound or high basal levels of antibodies or to be done in case of graft dysfunction .
Accommodation
accommodation is facilitated by the reduction of the isoagglutinin level, by the blockage of complement activation and by RTX. IA- specific columns may facilitate the phenomenon.
Role of protocol biopsies
role on protocol biopsies of C4d in transplantations involving ABOi seems to be related to accommodation when found in
the absence of clinical or other histological abnormalities.
Complications
Haemorrhages are most common in ABOI transplant.
Infections are more common in ABOi transplant.
The incidence of ABMR ranges between 10% and 30% and occurs usually in the first 2 weeks.
KPD
Some points need clarification
Transportation of kidneys vs donor travel
Simultaneous vs no simultaneous exchanges
Closed chains vs open chains
MAKING A CHOICE BETWEEN DESENSITIZATION AND KPD
KPD is generally cheaper with respect to desensitization,but time is needed to find a suitable donor whereas desensitisation is costly but transplant has no delay.
You can still have plasma cells circulating, producing antibodies.