The analysis of some of the most important recent studies dealing with Tregs used as possible biomarker of acute kidney transplant rejection and/or prognostic factor related to the graft survival (see Table 1) inspires some critical observations. First of all it must be pointed out that most of the times the final assessment of the studies is affected by the modest statistical validity of the analyzed sample due to the small
number of patients included. The consideration that analysis of Foxp3 mRNA and Foxp3+ CD4+ T cells is often performed on bioptic samples
is a critical element to take into account. The use of a graft survival biomarker could be able to improve the prognostic validity of the procedure, also in terms of evaluation of response to immunosuppressive therapies. On the other
hand, it must be considered that renal biopsying for the diagnosing of allograft rejection is an invasive and timeconsuming procedure with some risk of complications and not easily manageable for all patients. Therefore, in the
general followup of transplanted patients, a noninvasive test could be more advantageous, although this option still needs to be confirmed on additional cohorts taking into account all
the aspects considered earlier. Lastly, the different immunosuppressive therapies employed in the available studies and the potential effects on Treg expression and function constitute another critical variable to take into account in the evaluation of Treg function in the allograft outcome. Recent clinical studies have
demonstrated how different immunosuppressive drugs can influence differently the number and function of Tregs, by inducing stimulation, inhibition, or even noninterference. In particular, while corticosteroids and rapamycin have been
shown to improve the suppressive activity and survival of Tregs, other treatments as calcineurin inhibitors (CIs) have been shown to affect Treg function [56]. However, it is difficult to differentiate the effects of different immunosuppressants, although the use of selective pharmacological
treatments able to regulate the suppressive function of Tregs would be attractive in organ transplantation.
Mohammed Sobair
3 years ago
Acute rejection (AR) is responsible for up to 12% of graft loss with the highest risk
generally occurring during the first six months after transplantation. AR may be broadly
classified into humoral as well as cellular rejection. Cellular rejection develops when
donor alloantigens, presented by antigen-presenting cells (APCs) through class I or
class II HLA molecules, activate the immune response against the allograft, resulting in
activation of naive T cells that differentiate into subsets including cytotoxic CD8+ and
helper CD4+ T cells type 1 (TH1) and TH2 cells or into cytoprotective immunoregulatory
T cells (Tregs). The immune reaction directed against a renal allograft has been
suggested to be characterized by two major components: a destructive one, mediated by
CD4+ helper and CD8+ cytotoxic T cells, and a protective response, mediated by Tregs.
The balance between these two opposite immune responses can significantly affect the
graft survival. Many studies have been performed in order to define the role of Tregs
either in the immunodiagnosis of transplant rejection or as predictor of the clinical
outcome. However, information available from the literature shows a contradictory
picture that deserves further investigation. .
Nadia Ibrahim
3 years ago
Please summarise the different roles of T reg in transplantation. Acute rejection is classified into Antibody mediated ( humoral) and cellular rejection. Cscade of Cellular rejection starts when APC s present Donors Ag (HLA class I and II) to recipients T lymphocytes resulting in activation of naive T cells that differentiate into subsets including cytotoxic CD8+ and helper CD4+ T cells type 1 (TH1) and TH2 cells or into cytoprotective immunoregulatory T cells (Tregs). (5) CD4 + and CD8+ are considered the destructive arm of Alloimmune response against the graft, They infiltrate into the transplanted kidney, where they release cytokines and chemokines, causing cell death either directly or indirectly [6]. However T reg cells are the protective arm. The balance between both opposite immuneresponses can significantly affect the graft survival [7]. Tregs were identified as a CD4+ Tcell subpopulation expressing CD25 [14]and cytotoxic T-lymphocyte antigen 4” (CTLA-4) Originate mainly from the thymus (natural, nTregs) and from the peripheral conversion of naive CD4+ Tcells under appropriate stimulus conditions (induced, iTregs) ( 20]. Treg cells prevent the activation of autoreactive immune responses , induce and mentain tolerance , contribute to maintaining homeostasis of the microbial flora of the gut, and promote the immunogenic escape of cancer cells [11]. Activation pf Treg cells occur after exposure inflamed tissues where the local cytokine In particular TGF-𝛽,IL-10,andIL-2 or play a role in their activation and regulation , or by exposure to environmental conditions such as those produced by tumors [28]. Tregs can control DC activity by multiple mechanisms, and this results in the inhibition of effector T cell activation and promoting of functional tolerance. Tregs produce IL-10, which is able to inhibit, either directly or indirectly, effector T cell activity during infection, autoimmunity, and cancer [30]. On the other hand Tregs expressing CTLA-4 down regulate the expression of the costimulatory molecules CD80 and CD86 on DC ending in impaired costimulation via CD28 and defective T cell stimulation. [42]. Tregs can also induce perforin-dependent cytolysis of DCs in tumour-draining lymph nodes [45]. Many studies found that higher peripheral Treg levels in blood was associated with better graft survival and outcome, hence it could be used as a prognostic factor assessing and predicting graft outcome References:
(5) S.Schaub,J.A.Wilkins,D.Rush,andP.Nickerson,“Developing a tool for noninvasive monitoring of renal allografts,” Expert Review of Proteomics,vol.3,no.5,pp.497–509,2006. [6] B. J. Nankivell and S. I. Alexander, “Rejection of the kidney allograft,” The New England Journal of Medicine,vol.363,no. 15, pp. 1451–1462, 2010. [7]X.X.Zheng,A.S´anchez-Fueyo,M.Sho,C.Domenig,M.H. Sayegh, andT.B.Strom,“Favorablytippingthebalancebetween cytopathic and regulatory T cells to create transplantation tolerance,” Immunity,vol.19,no.4,pp.503–514,2003. (11) S. Sakaguchi, T. Yamaguchi, T. Nomura, and M. Ono, “Regulatory T cells and immune tolerance,” Cell,vol.133,no.5,pp. 775–787, 2008. (14) S. Sakaguchi, N. Sakaguchi, M. Asano, M. Itoh, and M. Toda, “Immunologic self-tolerance maintained by activated T cells expressing IL-2 receptor 𝛼-chains (CD25): breakdown of a single mechanismofself-tolerance causes various autoimmune diseases,” Journal of Immunology, vol. 155, no. 3, pp. 1151–1164, 1995. (20) M. O. Li, S. Sanjabi, and R. Flavell, “Transforming growth factor-𝛽 controls development, homeostasis, and tolerance of T cells by regulatory T cell-dependent and -independent mechanisms,” Immunity,vol.25,no.3,pp.455–471,2006. 28] M. D. Sharma, B. Baban, P. Chandler et al., “Plasmacytoid dendritic cells from mouse tumor-draining lymph nodes directly activate matureTregsviaindoleamine2,3-dioxygenase,”Journal of Clinical Investigation,vol.117,no.9,pp.2570–2582,2007. [30] K. Loser, J. Apelt, M. Voskort et al., “IL-10 controls ultravioletinduced carcinogenesis in mice,” Journal of Immunology,vol. 179, no. 1, pp. 365–371, 2007. [42] O.S.Qureshi,Y.Zheng,K.Nakamuraetal.,“Trans-endocytosis of CD80 and CD86: A molecular basis for the cell-extrinsic function of CTLA-4,” Science,vol.332,no.6029,pp.600–603, 2011. [45] A. Boissonnas, A. Scholer-Dahirel, V. Simon-Blancal et al., “Foxp3+ Tcells induce perforin-dependent dendritic cell death in tumor-draining lymph nodes,” Immunity,vol.32,no.2,pp. 266–278, 2010.
Amit Sharma
3 years ago
Please summarise the different roles of Treg in transplantation.
Regulatory T cells (Treg) are CD4 positive T cells which express CD25 and CTLA4 with low CD127. In aadition, they are positive for demethylated FOXP3. They comprise approximately 5% of total lymphocytes in blood and are very important for tolerance.
Treg may be either natural (nTreg) or induced (iTreg) which remain dormant and get activated by inflammation (through TGF beta, Interleukin 10 and Interleukin 2), malignancy and T Cell receptor (TCR) engagement inhibiting effector T cell activation causing tolerance or helper response.
Treg may also be classified as a) Naive (resting) Treg cells (FOXP3+ CD45RA+), b) activated (effector) Treg cells (FOXP3+++ CD45RA-) and c) FOXP3+ effector (cytokine producing) cells (FOXP3+ CD45RA-): which release proinflammatory cytokines liken IL-2, IL-17, Interferon gamma and have no immunosuppressive function.
Treg release IL-10 inhibiting effector T cell activity associated with infection, autoimmunity and cancers. Through CTLA-4, Treg inhibit co-stimulation on dendritic cells and cause perforin dependent dendritic cell lysis.
Increased urinary FOXP3 in transplant recipients with acute rejection has been shown to be associated with more responsiveness to steroids and decreased rates of graft failure.
In a study involving protocol biopsies, interstitial T lymphocyte infiltration was associated with no acute rejection episodes if it was FOXP3 positive while those with Granzyme B positivity developed acute rejection within one year. Patients with increased circulating Treg levels have been shown to be associated with better graft survival. It has been shown that steroids and mTOR inhibitors increase Treg survival while CNI affect Treg function.
TRACT trial, conducted in US was performed in living kidney transplant recipients receiving Alemtuzumab induction with MMF and Tacrolimus which was converted to sirolimus at day 30 and Treg infusion at day 60. It showed no opportunistic infection and no episode of acute rejection at 2 years in all the patients. (1)
TASK trial, conducted in UK, was performed in patients with subclinical inflammation on 6 month protocol biopsies (Banff i & t <2) showed no inflammation and graft dysfunction at 12 months, after receiving Treg infusion. (1)
Reference:
1) Atif M, Conti F, Gorochov G, et al. Regulatory T cells in solid organ transplantation. Clin Transl Immunology 2020;9:e1099
Mahmoud Hamada
3 years ago
T reg is crucial for peripheral tolerance.
they are concerned with suppression of immune response.
therapy with T reg lead to decrease in immune response in a trial on a murine model with decrease in DSA level.
Dalia Ali
3 years ago
Principal Mechanisms of T-Cell-Mediated AR
Transplant rejection is the consequence of the recipient’s alloimmune response and consists of manifested deterioration or complete function loss of the transplanted organ
AR classified into humoral and cellular rejections
Different cell types are involved in the graft rejection including T and B cells, macrophages, plasma cells, eosinophils, and neutrophils.,
T cells play a crucial role either in mounting and/or regulating alloreactive responses. T he main targets of cell-mediated damage are the tubular epithelium and the endothelium.
acute allograft rejection starts when the recipient’s T cells recognize the donor alloantigens presented by APCs
T cell infiltration into the graft is mainly at the level of postcapillaryvenuleendothelium.Threemainstepscanbe identified: tethering, adhesion, and transmigration[
Treg and Tolerance
Tregs play a critical role in the maintenance of T cell homeostasis under different immune conditions.
Origin of Tregs. Tregs were identified as a CD4+ Tcell subpopulation expressing CD25 moleculeand“cytotoxic T-lymphocyte antigen 4” (CTLA-4) at a similar extent to that displayed by activated T cells [15, 16].
The presence of CTLA4 and the release of inhibitory cytokines including IL-10 and IL-35 suggestedasuppressorphenotypeforthesecells andcriticalroleincontrollingtheactivationandfunctionof Tlymphocytes as well as of APC and NK cells.
Circulating Pool and Activation of Tregs
Tregs are essential for maintaining peripheral tolerance; nevertheless, they show a quiescent phenotype when isolated from a noninflammatory environment and require functional activation fortheacquisitionofTregfullfunctionalsuppressiveactivity ]thatcanbeachievedfollowingexposuretoself-antigens or to antigens presented at mucosal surfaces where they can be recruited. Tregs can also be functionally activated while migrating through inflamed tissues, or by exposure to environmental conditions such as those produced by tumors
Regulation of Immune Responses by Tregs
Tregs produce IL-10, which is able to inhibit, either directly or indirectly, effector T cell activity during infection, autoimmunity, and cancer
Regulation of immune functions mediated by CTLA-4expressing Tregs depends on the ability of CTLA-4 molecule to downregulate the expression of costimulatory molecules CD80andCD86ondendriticcells(DCs)oflymphoidtissues resulting in impaired costimulation via CD28 and defective Tcell stimulation
Regulatory T Cells in the Immunodiagnosis and Outcome of Kidney Allograft Rejection
T he consideration that analysis of Foxp3 mRNA and Foxp3+ CD4+ T cells is often performed on bioptic samples is a critical element to take into account. The use of a graft survival biomarker could be able to improve the prognostic validity of the procedure, also in terms of evaluation of response to immunosuppressive therapies.
Ahmed Omran
3 years ago
Role in T reg cells
They balance ;through their protective effect ,the destructive effect played by other T cells.
they are subset of CD+ cells and they inhibit pro inflammatory activities of CD4+and CD8+ effector cells , NK cells and APCs .They express CD4,CD25,FOXP3and CTLA-4.
Suppressive T reg activity maintenance is related to inflammatory cytokines like IL-2 &10 and TGF-B.CTLA-4 combats co stimulation targeting CD28 via downregulation of CD80 and 86 expression .Loss of CTLAw-4 in T reg cells leads to severe lymphoproliferative and autoimmune disease. T reg cells have important role in improving graft survival and evolving tolerance .High level of FOXP3 was associated with favorable response to steroids and lower risk of graft failure in patients with acute rejection .It was found that level of circulating T reg is correlated to graft survival ;when more than 70%at 6 and 12 months after Tx are associated with better graft survival at 5 years.
Steroids and rapamycin were found to improve T reg functions. On the other hand, CNI decreased number and function of T reg cells.
Mohamed Essmat
3 years ago
Role of T reg in transplantation Treg is an important component of the immune system and it represent the beneficial arm of immune response .it represents about 5% of total lymphocytes and plays key role in maintenance of T cellshomeostasis : It controls the activation and function of T cells, APCs, & NK cells as well as Control of immune responses in lymphoid and non-lymphoid tissue. ProducesIL-10 ; the inhibitor of the effector T cells activity during infection, auto-immunity, and cancer The CTLA-4 expressing Treg down regulate the expression of co-stimulation molecules in CD80 and CD86 on Dendritic cells resulting in dysfunctional co-stimulation via CD 28 .They induceperforin-dependent cytolysis of the Dendritic cells in tumour-draining lymph node. High levels of FOXP3 are associated with high levels of interstitial inflammation & tubulitis.T reg is opposing the inflammatory states associated with kidney transplantation and this may be considered as a prognostic factor of graft outcome.
Nazik Mahmoud
3 years ago
T reg is subpopulation of CD4 T helper cells, it represent 5% of circulating T lymphocytes, orignate from the thymus,it has Immun protective effect as the regulatory mechanism . It express CD25 and released IL-10 and CTL-A4 , work by many transcripter like grazymes and FOXP3 to suppress T cells in autoimmune disease and cancers.
The follow up and measurement of those molecules will give a clue about graft status, survival and possibility of Acute or chronic rejection either T cell mediated rejection or antibodies mediated rejection. They contribute to maintain peripheral tolerance.
Nasrin Esfandiar
3 years ago
There are two types of Tregs: one which originate from thymus ( nTregs) and the other one by stimulus from CD4+ T cells (iTregs). Tregs are subtypes of CD4+ T cell that express CD 25 and CTLA-4 and release IL-10 and IL-35 and have suppressor effects for T cells, APC and NK cells. FOXP3 transcription factor causes transforming from naive T cell CD4 + to iTregs. TGF-β, IL10 and IL-2 contribute in function of Tregs. CTLA-4 expressing Tregs down-regulate CD80 costimulatory on DCs. Tregs can induce tolerance to graft. FOXP3 expression could be transient during T cell activation. So these cells can differentiate into cytotoxic cells that have an active role in rejection or into Tregs with regulatory function. Foxp3/IL-17 ratio could be a predictor marker for TX outcome. This idea is attractive but needs more investigation to use these makers. Corticosteroid and rapamycin improve function of Tregs but CNIs can suppress Tregs.
Reem Younis
3 years ago
-Acute rejection (AR) is responsible for up to 12 % of graft loss commonly within the first 6 months after transplantation.AR can be classified into humoral and cellular rejection.
-Cellular rejection develop when donor alloantigen, presented by an antigen-presenting cell (APCs) through class I or class II HLA molecules, activate an immune response against the allograft, resulting in activation of naïve T cell which differentiates into cytotoxic CD8+ and helper CD4+cells (TH1) and TH2 or cytoprotective immunoregulatory T cell (Tregs), also Tregs cell originate from the thymus gland.
-Tregs in CD4+T cell expressing CD25 and T lymphocyte antigen 4 (CTLA-4).
-Treg cells are about 5% of T lymphocytes.
-Tregs maintain T cell homeostasis
-prevent activation of autoreactive immune response
-contribute to maintaining self-tolerance and homeostasis of the microbial gut flora
-promote the immunogenic escape of cancer cells.
-Tregs produce IL- 10 which inhibit, either directly or indirectly effector T cells during infection, autoimmunity, and cancer.
-CTLA-4 –expressing Tregs can down-regulate the expression of costimulatory molecules CD80 and CD86 on dendritic cells of lymphoid tissues resulting in impaired co stimulation via CD 28 and defective T cell stimulation.
-Treg cells can inhibit dendritic cells(DC) by stable Treg-DC contact lead to Tregs- mediated inhibition and also Tregs can induce perforin-dependent cytolysis of DC.
-Foxp3 in the urine analysis was high in patients with acute rejection and associated with better response to steroids and lower risk for graft failure.
-Multivariate analysis revealed that Foxp3/IL-17 ratio was a significant predictor for allograft outcome.
-Patients who maintain high Treg levels at both 6 and 12months display better long-term graft survival at 4qnd 5 years follow up.
-According to Banff classification, higher Foxp3 expression was associated with higher levels of interstitial inflammation and tubulitis.
–
MICHAEL Farag
3 years ago
The immune reaction directed against a renal allograft has been suggested to be characterized by two major components: a destructive one, mediated by CD4+ helper and CD8+ cytotoxic T cells, and a protective response, mediated by Tregs. The balance between these two opposite immune responses can significantly affect the graft survival.
Antibody-mediated rejection is characterized by the presence of an antibody infiltration into the transplanted kidney, targeting HLA antigens on the peritubular and glomerular capillary endothelia, which results in complement activation, cytokine and chemokine release, and induction of adhesion molecules.
Cellular rejection develops when donor alloantigens, presented by antigen-presenting cells (APCs) through class I or class II HLA molecules, activate the immune response against the allograft, resulting in activation of naive T cells that differentiate into subsets including
cytotoxic CD8+ and helper CD4+ T cells type 1 (TH1) and TH2 cells or into cytoprotective immunoregulatory T cells (Tregs). CD4+ and CD8+ T cells infiltrate into the transplanted kidney, where they release cytokines and chemokines, causing cell death either directly or indirectly.
Different cell types are involved in the graft rejection including T and B cells, macrophages, plasma cells,eosinophils, and neutrophils. T cells play a crucial role either in mounting and/or regulating alloreactive responses.
T cell infiltration into the graft is mainly at the level of postcapillary venule endothelium. Three main steps can be identified: tethering, adhesion, and transmigration.
Treg and Tolerance Tregs play a critical role in the maintenance of T cell homeostasis under different immune conditions. They prevent the activation of autoreactive immune responses, contribute to
maintaining self-tolerance and homeostasis of the microbial flora of the gut, and promote the immunogenic escape of cancer cells.
Origin of Tregs: Tregs were identified as a CD4+ T cell subpopulation expressing CD25 molecule and “cytotoxic T-lymphocyte antigen 4” (CTLA-4) at a similar extent to that
displayed by activated T cells. The presence of CTLA-4 and the release of inhibitory cytokines including IL-10 and IL-35 suggested a suppressor phenotype for these cells and critical role in controlling the activation and function of T lymphocytes as well as of APC and NK cells.
Tregs originate mainly from the thymus (natural, nTregs) and from the peripheral conversion of naive CD4+ T cells under appropriate stimulus conditions (induced, iTregs)
Circulating Pool and Activation of Tregs. Circulating Tregs represent 5% of total lymphocytes in blood. Tregs are essential for maintaining peripheral tolerance; nevertheless,
they show a quiescent phenotype when isolated from a noninflammatory environment and require functional activation for the acquisition of Treg full functional suppressive activity that can be achieved following exposure to self-antigens or to antigens presented at mucosal surfaces where they can be recruited. Inflammation plays an important role in driving the local
cytokine milieu. In particular TGF-𝛽, IL-10, and IL-2 have been shown to be critical in regulating activation and/or maintenance of the immunosuppressive functions of Tregs
Regulation of Immune Responses by Tregs.
Tregs produce IL-10, which is able to inhibit, either directly or indirectly, effector T cell activity during infection, autoimmunity, and cancer.
Regulation of immune functions mediated by CTLA-4- expressing Tregs depends on the ability of CTLA-4 molecule to downregulate the expression of costimulatory molecules CD80 and CD86 on dendritic cells (DCs) of lymphoid tissues resulting in impaired costimulation via CD28 and defective T cell stimulation.
Regulatory T Cells in the Immunodiagnosis and Outcome of Kidney Allograft Rejection
In the search of biomarkers for the diagnosis of cell mediated AR and prognosis of renal transplant, an increasing attention has been paid to the role of Tregs.
The analysis of some of the most important recent studies dealing with Tregs used as possible biomarker of acute kidney transplant rejection and/or prognostic factor related to the graft survival inspires some critical observations. First of all it must be pointed out that most of the times the final assessment of the studies is affected by the modest statistical validity of the analyzed sample due to the small number of patients included. On the otherhand, it must be considered that renal biopsying for the diagnosing of allograft rejection is an invasive and time consuming procedure with some risk of complications and
not easily manageable for all patients. Lastly, the different immunosuppressive therapies employed in the available studies and the potential effects on Treg expression and function constitute another critical variable to take into account in the evaluation of Treg function in the allograft outcome.
Tahani Hadi
3 years ago
Treg are CD4 T cells with 2 subtypes according to from where they originate : n treg are natural that are originate in the thymus while peripheral treg originate from convertion native T cells peripherally, treg represent 5% of the total lymphocytes and more treg level means better graft outcome because they play important role in controlling immune response and effector T cells activity through IL-10 production ,treg characterized by express CD 25 and cytotoxic T lymphocytes Ag which will help to down regulate co stimulatory molecules on the dendritic cells of lymphoid organs and this will affect on T cell stimulation, there are markers that are used to detect treg activity like FOXP3 and IL-17 and by determining their percentage graft survival and rejection risk can be evaluated .
Mujtaba Zuhair
3 years ago
Treg cells plays an important role in graft tolerance. There are 2 types of Treg : thymus derived Treg and peripheral Treg ( it derived from naïve T cells in the periphery and is also called induced Treg)
Treg had many functions :
It secret IL-10 which inhibit other T cells .
It interact with DC through CTLA-4 Ag which bind to CD80/86 so preventing the costimulation signal for T cell activation.
It can kill DC cells by perforin mediated cytolysis and prevent DC from antigen presentation to T cells.
The use of Treg in the field of diagnosis has been studied by many studies :
FOX-3 expression is increased in acute rejection.
Combination of Foxp3 and serum creatinine is a good predictor of rejection reversal than serum creatinine alone or FOX-3 alone.
Higher level of Foxp3 expression in acute rejection is associated with better response to steroids.
Higher level of Foxp3 expression is associated with less progression of graft damage after acute rejection.
Foxp3/IL17 ratio has significant correlation with graft survival.
The higher level of Treg in the peripheral blood is is associated with better outcome.
Mahmud Islam
3 years ago
Acute rejection is through different mechanisms one of which is by native T cells. they differentiate into cytotoxic or helper (TH1/TH2) or cytoprotective immunoregulatory T cells (Treg). Balance among these mechanisms is important.
Tregs:
play role in maintaining T cell homeostasis.
prevent activation of autoreactive immune response contributing to the maintenance of self-tolerance
by the production of IL-10 play role in the inhibition of t cell activity
can also induce perforin-dependent cytolysis of denatured cells in tumor-draining lymph nodes.
In a study of 90 patients, the high level of Treg cells was associated with higher graft survival at 4 and 5 years
Esmat MD
3 years ago
Naïve T cells after activation differentiate into subsets of cytotoxic CD8+ and helper CD4+ T cells (TH1 and TH2) or into cytoprotective immunoregulatory T cells (Treg).
The immune reaction against a renal allograft has two main components: a destructive one mediated by CD4+ or CD8+ cytotoxic T cells and a protective response mediated by Tregs, and the balance between them identifies the fate of the graft and its survival.
Different roles of regulatory T cells in kidney transplantation:
Tregs and tolerance
Tregs originate mainly from the thymus (nTregs) or form from peripheral naïve T cell differentiation (iTregs).
Tregs prevent the activation of autoreactive immune responses and play a critical role in the maintenance of T cell homeostasis. Tregs express CD25 and CTLA-4 and release inhibitory cytokines including IL-10 and IL-35 that suggests a suppressor phenotype for these cells and a critical role in controlling the activation and function of T lymphocytes as well as of APC and NK cells.
Circulating Tregs present 5% of total lymphocytes in the blood. For the acquisition of full functional suppressive activity, Tregs need to be exposed to self-antigens or inflammation milieu. Inflammation plays an important role in the production of cytokines such as IL-10, TGF-beta, and Il-2, which are critical in the regulation of the immunosuppressive activity of Tregs.
Several mechanisms have been proposed to explain the role of Tregs in modulating immune response, such as:
IL-10 production that inhibits effector T cell activity.
The ability of CTLA-4 molecule to down regulate the expression of costimulatory molecules CD80 and CD86 on DCs, and as a result, inhibition of their activity.
Induction of perforin-dependent cytolysis of DCs
Therefore, Tregs can control DC activity by multiple mechanisms, and this results in the inhibition of effector T cell activation and promoting of functional tolerance.
Regulatory T Cells in the Immunodiagnosis and Outcome of Kidney Allograft Rejection
Identification of biomarkers to be able to discriminate between rejection and other causes of inflammation as well as correlating with outcome is a research challenge, and attention has been paid to the role of Tregs.
Induction of allograft tolerance by Tregs are not necessarily associated with reduction of response to the pathogens, so it is a promising approach in clinical transplantation.
FOXP3 transcripts, as a specific marker of Tregs, can be used as a prognostic marker of rejection reversal.
In one study, the higher level of FOXP3 transcripts in the urine sample of patients with acute rejection was observed. Indeed, transient expression of FOXP3 can be normal consequence of T cell activation without acquisition of the Treg phenotype. In addition, acute rejection with higher level of urinary FOXP3 correlated better with steroid responsiveness and better graft survival. In another study, correlation between FOXP3 and acute rejection showed the highest significance (94% sensitivity and 95% specificity).
A study reported that acute rejection was less common in the regulatory group of recipients (Foxp3+-infiltrating T lymphocytes in biopsies) than cytotoxic phenotype (dominated by Granzyme B+-T lymphocytes).
By an increasing the IL-17 to FOXP3 ratio, the allograft function significantly decreased in the acute cell mediated rejection setting.
In addition, patients with a higher levels of circulating Treg were associated with better long-term survival.
Tregs may play a role in antagonizing the inflammatory state associated with kidney transplantation. However, there are controversy in different studies about this vision.
Asmaa Khudhur
3 years ago
Following exposure to antigens and activation of costimulatory molecules, peripheral naive CD4+ T cells can differentiate into different subpopulations : T helper 17 (Th17), Th1, Th2, and iTregs . Several transcription factors contribute to the functional specialization of these subsets, including Foxp3, ROR𝛾t, T-bet, and GATA3, which activate genes involved in the control of T cell function .
Tregs play a critical role in the maintenance of T cell homeostasis under different immune conditions. They prevent the activation of autoreactive immune responses, contribute to maintaining self-tolerance and homeostasis of the microbial flora of the gut, and promote the immunogenic escape of cancer cells .
In the search of biomarkers for the diagnosis of cell- mediated AR and prognosis of renal transplant, an increasing attention has been paid to the role of Tregs.
Inflammation plays an important role in driving the local cytokine milieu. In particular TGF-𝛽, IL-10, and IL-2 have been shown to be critical in regulating activation and/or maintenance of the immunosuppressive functions of Tregs
Tregs can control DC activity by multiple mechanisms, and this results in the inhibition of effector T cell activation and promoting of functional tolerance.
Foxp3/IL-17 ratio was a significant predictor for allograft outcome.
The level of circulating Tregs at peripheral blood level are associated with good long-term graft survival
In this case a combination of Foxp3 transcripts and creatinine levels proved to be a better prognosticator of rejection reversal than Foxp3 transcripts or serum creatinine levels alone.
Tregs may play a role in antagonizing the inflammatory state associated with kidney transplantation and may possibly be considered as a prognostic factor of outcome.
Ben Lomatayo
3 years ago
Different role of T reg in transplantation ; T reg is important component of the immune system and it represent the beneficial arm of rejection .They are about 5% of total lymphocytes and plays key tole in maintenance of T cells homeostasis and microbial flora of the gut homeostasis. Their role are summarised below ;
Control the activation and function of T cells, APCs, & NK cells
Control of immune responses in lymphoid and non-lymphoid tissue
Produces IL-10 ; the inhibitor of the effector T cells activity during infection, auto-immunity, and cancer (30,31)
The CTLA-4 expressing Treg down regulate the expression of co-stimulation molecules in CD80 and CD86 on Dendritic cells resulting in dysfunctional co-stimulation via CD 28 (43,44)
They induce perforin-dependent cytolysis of the Dendritic cells in tumour-draining lymph node(45)
They are important in immuno-diagnosis and outcome of kidney graft rejection ;FOXP3 transcripts shown is to be high in patients with AR(22). Both FOXP3 & SCr are better for prognostic rejection reversal than either of the test taken alone. High levels of FOXP3 is associated with high levels of interstitial inflammation & tubulitis.
T reg is opposing the inflammatory states associated with kidney transplantation and this may be considered as prognostic factor of graft outcome.
saja Mohammed
3 years ago
Regulatory T Cells in the Immunodiagnostic and Outcome of Kidney Allograft Rejection Introduction:
Tregs represent 5% of total lymphocytes in blood. essential for maintaining peripheral tolerance:Tregs have cytoprotective and immune modulating effect Tregs play a critical role in the maintenance of T cell hemostasis under different immune conditions. their role in the immunodiagnostic of the acute rejection and the transplant outcome is diverse and need more understanding. Aim of this study:
to identify the Treg cells effect in acute cellular rejection and assess their role as immunological biomarker that can predict the clinical transplant outcome.
Treg types:
1- (natural, nTregs) originated mainly from the thymus
2-(induced, iTregs) from CD4 subset activation and proliferation in secondary lymphoid tissue as part of costimulatory signal of Tcell activation. Tregs effect on immune response.
Treg cells control the immune system in lymphoid and non-lymphoid tissues by many different mechanisms.
Inflammation triggers the expression of many local cytokines like TGF-𝛽, IL-10, and IL-2 which have very critical role in regulating activation and/or maintenance of the immunosuppressive functions of Treg cells soTreg cells can control the DCs activation by many mechanisms that lead to immune modulation and tolerance induction, for example the Treg cells expressing IL10 have direct and indirect inhibitory effectonthe T effector cells during infection , cancer and autoimmunity .while selective deletion of IL10 in Treg results in the development of spontaneous colitis, and activated immune responses at the skin level and lung interfaces. Treg effect on immune function:
CTLA-4-expressing Tregs depends on the ability of CTLA-4 molecule to inhibit the expression of the CD80 / CD86 on dendritic cells (DCs) of lymphoid tissues resulting in impaired costimulation via CD28 and defective T- cell stimulation, Tregs can also induce perforin-dependent cytolysis of DCs in tumor-draining lymph nodes studies show stable contacts between Treg cells and APCs dendritic cells, confirming Treg cells mediated downregulation of these cells. and this results in the inhibition of effector T cell activation and enhance the functional immune tolerance and now on going clinical trails on using mAB to block some of the these costimaltory pathways .
Regulatory T Cells in the Immunodiagnosis and Outcome of Kidney Allograft Rejection
Nowadays there is increase interest about the role of Treg cells molecular markers for the diagnosis of T- cell mediated AR and as prognostic indicator of renal transplant outcome.
a direct and active involvement of Treg-mediated T cell suppression at the site of the tolerated transplants has been demonstrated, the specificity for donor antigens has not been fully evidenced.
In this review article, of total 8 studies with small numbers of patients range of 30-125 by using different Treg expressing markers including Foxp3 using real-time PCR from urinary cells or Treg FOXP3, m RNA, FOXP3 /1L17 expression cytolytic markers (perforin, granzyme B, and fas-ligand), peripheral blood mononuclear cell. All analyzed Treg -transcripts markers were higher in AR groups from different reported studies.
Muthu Kumar et al. in his study of 89 KT recipients assess the urinary FOXP3 as predictor for AR and found higher urinary Terg FOXP3 in the AR group (36 patients) as compared with the other two groups in addition patients who displayed both AR and higher urinary Foxp3 level showed better responsiveness to steroid treatment in 26 patients with significantly lower risk for graft failure as compared with subjects with lower levels of the transcription factor.
In another recent study from same author (Muthukumar et al), report that the urinary Foxp3 ,mRNA profiles and other molecules where able to associate with an early steroid withdrawal regimen with antithymocyte globulin induction, with excellent graft and patient outcomes in HIV-infected recipients of kidney allografts.
Another study by Mansour et al. [38] measured mRNA levels of Foxp3, Granzyme B, IFN-𝛾, IL-23, and ROR𝛾t in renal tissue of 46 untreated subjects with renal allografts with borderline rejection by Banff score Twenty-five patients were considered “nonprogressive,” as defined by serum creatinine
level below 110% of baseline during the 40 days following biopsy. While 21 patients were considered “progressive, as defined by an increase in serum creatinine level more than110% of baseline and by repeated histologic examinations showing AR,Ithe higher levels of Foxp3 mRNA were found in the nonprogressive group as compared with those observed in the progressive group.
Chung et al, assess the clinical significance of the ratio between IL-17-secreting cells and Treg infiltration in renal allograft tissues with acute T-cell-mediated rejection (ATCMR) in 56 patients and he confirm significant reduction in graft function in the groups with 1L17 higher ratio, with more sever IFTA, and lower 1-year and 5-year graft survival rates compared with patients with FOXP3 high ratio. with Multivariate analysis confirm that Foxp3/IL-17 ratio was a significant predictor for allograft outcome.
Tregs level at peripheral blood and the association with long-term graft survival were analyzed by flow cytometry in 90 kidney transplant recipients [41]. Patients who maintained high Treg levels (above 70%) at both 6 and 12 months shows a better long-term graft survival at 4- and 5-years follow-up.
Another study by Veronese et al. [35] he analyzes 73 graft biopsies and he reported that Tregs cells significantly higher in ACR type I and type II, with significant lower survival rate upon two years FU with higher Foxp3 score as compared with that observed in AHR and CNI toxicity; 96%Foxp3+ cells were CD4+ T lymphocytes aggregated within renal tubules.
CD4 positivity, and not Foxp3 mRNA expression, was independently associated with graft survival.as per Bunnag et al, study (36).
Concluding marks:
1-Small sample size in most of the reviewed studies can affect the final assessment and the validity of analyzed data.
2-Use the graft biopsy for diagnosis of rejection is rather invasive, and not without risk of complications
3-Moving toward a noninvasive molecular test could be more beneficial but still need more studies to confirm their validity
4-The use of a graft survival biomarker could be able to improve the prognostic validity of the procedure.
5-The effect of the different Immunosuppressive therapy used and its effect of the expression / function of Treg and CD 4 its very important variable to be reconsider in the evaluation of Treg function in the allograft outcome for example the rapamycin and steroid known to enhance and maintain the suppressive activity of Treg as compared to CNI effect. However, still difficult to differentiate the effects of different immunosuppressants,
One of the future goals is to use selective immunosuppressive agents that maintain and stabilize the suppressive activity of Treg
Heba Wagdy
3 years ago
Tregs have a suppressive role, they control activation and function of T lymphocytes, APC and NK cells
Tregs are classified into natural Treg originating from thymus and induced TReg induced from stimulated peripheral conversion of naïve CD4+ T cells and are essential for maintaining peripheral tolerance. Regulation of the immune response by Treg occur via several mechanisms:
produce IL-10 which inhibit effector T cell activity during infection, autoimmunity and cancer
CTLA-4 expressing Tregs regulate immune function as it decrease the expression of costimulatory molecules CD80 and CD86 on dendritic cells (DC) leading to impaired costimulation via CD28 and inhibited T cell stimuli.
Studies showed that Treg could control DC activity resulting in inhibited effector T cells activation and increased functional tolerance.
Regulatory T cells and the outcome of kidney allograft rejection
Direct role of Treg in T cell suppression was demonstrated at the site of tolerated transplant but the specificity for donor antigen wasn’t evidenced.
Allograft tolerance mediated by Treg don’t necessarily impair the response to invading pathogens encouraging the development of tolerance induction protocols in clinical transplant
A study showed that level of Foxp3 transcripts (used as specific marker of Treg) and creatinine level could be predictors of rejection reversal with considering the heterogenous nature of cellular components of rejection as Foxp3 could be derived from T cell activation without gaining regulatory function.
Another study analyzed biopsies having interstitial T lymphocyte infiltration between tubules and showed that patients with Foxp3 infiltrating T lymphocytes in biopsies didn’t develop acute rejection during 5 years of follow up
Also patients who had high level of Treg in peripheral blood at 6 and 12 months, had better graft survival at 4 and 5 years of follow up
However other studies showed that number of Tregs was significantly higher in acute cellular rejection, intragraft expression of Foxp3 mRNA wasn’t associated with better allograft outcome and and Foxp3 expression was higher in kidneys with cellular, humoral and mixed rejection than in kidneys without rejection.
Recent studies showed that immunosuppressive drugs have different effect on number and function of graft, corticosteroids and rapamycin improve the suppressive activity and survival of Treg while calcineurins inhibitor affect Treg function, However it is difficult to differentiate the effect of different immunosuppression.
Fatima AlTaher
3 years ago
T reg are suppressor CD4 T lymphocytes with high expression of both CD25 and transcription factor FoxP3. They are either natural T reg (thymus derived )or induced peripheral T regs (iT reg). T reg are essential for identifying self from non self Ags, inducing natural tolerance through controlling alloreactive T cells , tissue repair and restrict cancer initiation .
The role of T reg in kidney transplantation rejection was evalutated in several study as
1- Muthukumar et study who found significantly higher urinary levels of FOXP3 in patients with graft dysfunction and it was higher also in patients who responded better to immune suppression after acute graft rejection attack that may high light the role of FOXP3 as a diagnostic and prognostic marker for graft function .
2- The ration between IL17 producing cell and T reg cells ( represented by FOXP3 level ) in patients with acute T cell mediated rejection ,revealed more advanced histological changes specially tubulointerstitial injury and poorer graft function and outcome I group with higher IL17 producing T cell infilteration.
3- The peripheral T reg cell examined by flowmetry correlated with better short term graft outcome.
However , other studies reveled the reverse as Kaplan-Meier study showed poor graft outcome in patients with higher FOXP3 levels. While Bunnag et al. reveleaded more aggressive histological changes in high FOXP3 group compared to normal graft function group
These differences may be attributed to different immunesuppression protocols used in these studies with their variable effects on T reg number and functions, so further studies are necessary to establish the use of T reg as diagnostic and prognostic marker for graft function.
Dalia Eltahir
3 years ago
Treg are originate fromTcell .Their role is to suppress the immune destrcution of Tc ,APC and NK through IL10,IL35 .
Treg are two types
Natural {nTreg} from the thymus and induced {iTreg }converted from naive Tcell peripherally .
principal mechanisms of T-cell- mediated AR
Antigen will be express in APC so can be recognize by T cell This lead to activation and differentiation of Tcell in to TH1,TH2,TH17 AND i Treg,this induce cellular rejection .Their site of action is the endothelium through integrin LFA-1 and transmigration .Infiltration of T cell in to interstium lead to destruction .The damege can be mediated
1- directly through TNF and INF .
2-Indirectly Tc cell .
Treg are associated with abetter response to therapy and low risk of graft failure .
Investigation of Treg done through many techniques ,estimation of Foxp3 in urine or renal tissue and peripheral blood or mRNA of Foxp3 in urine cell or renal biopsy .Also ratio between Treg in renal tissue and IL-17.
Some study found that cellular rejection associated with high level of Treg leading to poor survival rate and graft outcome .
To over come this differance large pt must be enrolled with universal immunosuppressive protocol and use of non invasive markers rather than biopsy .
Abdulrahman Ishag
3 years ago
Treg are CD4 subpopulation expressing both CD25 molecule and CTLA-4 (cytotoxic T lymphocyte antigen) . Tregs originate mainly from the thymus (natural, nTregs) and from the peripheral conversion of naive CD4+ T cells under appropriate stimulus conditions (induced, iTregs). Circulating Tregs represent 5% of total lymphocytes in blood. Treg regulate the immune response through production of IL-10,which is able to inhibit the effector T-cell activity . CTLA-4- expressing Tregs down regulate the expression of co stimulatory molecules CD80 and CD86 on dendritic cells (DCs) of lymphoid tissues resulting in impaired co stimulation via CD28 and defective T cell stimulation . Tregs can control DC activity by multiple mechanisms, and this results in the inhibition of effector T cell activation and promoting of functional tolerance. Treg can be used as a biomarker of acute kidney transplant rejection and prognostic factor of graft survival . The use of a graft survival biomarker could be able to improve evaluation of response to immunosuppressive therapies. Effects of immunosuppressive on Treg expression and function constitute another account in the evaluation of the allograft outcome. Corticosteroids and rapamycin have been shown to improve the suppressive activity and survival of Tregs.
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Assafi Mohammed
3 years ago
Roles of Treg in Transplantation.
Tregs were identified as a CD4+ T cell subpopulation expressing CD25 [14] molecule and “cytotoxic T-lymphocyte antigen 4” (CTLA-4) at a similar extent to that displayed by activated T cells.The presence of CTLA- 4 and the release of inhibitory cytokines including IL-10 and IL-35 suggested a suppressor phenotype for these cells and critical role in controlling the activation and function of T lymphocytes as well as of APC and NK cells.
Origin of Treg : Tregs originate mainly from the thymus (natural, nTregs) and from the peripheral conversion of naive CD4+ T cells under appropriate stimulus conditions (induced, iTregs).
The immune reaction directed against a renal allograft has been suggested to be characterized by two major components: a destructive one mediated by CD4+ helper and CD8+ cytotoxic T cells and a protective response mediated by Tregs. The balance between these two opposite immune responses can significantly affect the graft survival.
Circulating Pool and Activation of Tregs: Circulating Tregs represent 5% of total lymphocytes in blood and they show a quiescent phenotype when isolated from a noninflammatory environment.
Tregs require functional activation for the acquisition of Treg full functional suppressive activity and that can be achieved following:
exposure to self-antigens or to antigens presented at mucosal surfaces where they can be recruited.
and while migrating through inflamed tissues.
exposure to environmental conditions such as those produced by tumors.
Inflammation plays an important role in driving the local cytokine milieu. In particular TGF–𝛽, IL-10, and IL-2 have been shown to be critical in regulating activation and/or maintenance of the immunosuppressive functions of Tregs.
The role of Tregs either:
(i) in the immunodiagnosis of transplant rejection. or
(ii) as predictor of the clinical outcome.
Treg and Tolerance
Tregs play a critical role in the maintenance of T cell homeostasis under different immune conditions.
They prevent the activation of autoreactive immune responses.
Contribute to maintaining self-tolerance and homeostasis of the microbial flora of the gut.
Promote the immunogenic escape of cancer cells.
1.Regulation of Immune Responses by Tregs:
Tregs produce IL-10, which is able to inhibit, either directly or indirectly, effector T cell activity during infection, autoimmunity, and cancer. Selective deletion of IL- 10 in Tregs results in the development of spontaneous colitis and exaggerated immune responses at the skin level and lung interfaces.
The role of CTLA-4 has been suggested by the observation that its loss results in severe lymphoproliferative disease and spontaneous multiorgan autoimmunity.
Regulation of immune functions mediated by CTLA-4- expressing Tregs depends on the ability of CTLA-4 molecule to downregulate the expression of costimulatory molecules CD80 and CD86 on dendritic cells (DCs) of lymphoid tissues resulting in impaired costimulation via CD28 and defective T cell stimulation.
Studies have confirmed stable contacts between Tregs and DCs, confirming Treg-mediated inhibition of these cells.
Tregs can also induce perforin-dependent cytolysis of DCs in tumour-draining lymph nodes.
Tregs can control DC activity by multiple mechanisms, and this results in the inhibition of effector T cell activation and promoting of functional tolerance.
2.Regulatory T Cells in the Immunodiagnosis and Outcome of Kidney Allograft Rejection
A current research challenge is the definition of biochemical and/or histological markers which can be considered as early signs or predictive of rejection.
An ideal indicator should have the ability of discriminating between rejection and other causes of inflammation as well as to correlate with long-term prognosis and therapy efficacy.
(i) One of the most important studies dealing with the role of Tregs in renal transplantation is the work of Muthukumar et al. :
Urine samples from 83 kidney-transplant recipients were analyzed.
36 subjects showed graft dysfunction and biopsy-confirmed AR.
29 subjects had stable allograft function and normal allograft biopsy.
The levels of Foxp3 transcripts, as a specific marker of Tregs , in cells obtained from urine samples of the 36 subjects with AR were higher as compared with those observed in the other 2 groups analyzed. This result contrasted with the general expectation that Foxp3 should be lower in rejection.
Among the 36 episodes of AR, 26 successfully reversed, while 10 patients lost their grafts within 6 months following the acute episode of rejection.
A combination of Foxp3 transcripts and creatinine levels proved to be a better prognosticator of rejection reversal (90 percent sensitivity and 96 percent specificity) than Foxp3 transcripts (90 percent sensitivity and 73 percent specificity) or serum creatinine levels alone (85 percent sensitivity and 90 percent specificity).
(ii) In 2008, Aquino-Dias et al. analyzed the expression of perforin, granzyme B, and fas-ligand, together with Foxp3 using real-time PCR from urinary cells, peripheral blood mononuclear cells.
48 surveillance kidney biopsies from 35 patients with delayed graft functions, 20 of which showed histopathological features of AR and 28 of acute tubular necrosis.
All analyzed transcripts were higher in AR as compared with acute tubular necrosis.
Similar results and significant correlations were observed in kidney tissue, peripheral blood leukocytes, and urinary cells for all genes analyzed.
Although all correlations reached statistical significance, results concerning Foxp3 showed highest significance (94 percent sensitivity and 95 percent specificity).
In a very recent study from Muthukumar et al., the urinary cell mRNA profiles for Foxp3 and other molecules where able to associate an early steroid withdrawal regimen with antithymocyte globulin induction, with excellent graft and patient outcomes in HIV-infected recipients of kidney allografts.
(iii) Mansour et al. measured mRNA levels of Foxp3, Granzyme B, IFN-𝛾, IL-23, and ROR𝛾t in renal tissue obtained from 46 untreated subjects with renal allografts with borderline lymphocytic infiltrates according to Banff scheme (changes insufficient for diagnosis of AR, including foci of tubulitis with mild to moderate cortical infiltration and without intimal arteritis):
Twenty-five patients were considered “nonprogressive,” as defined by serum creatinine level below 110% of baseline during the 40 days following biopsy.
In contrast, 21 patients were considered “progressive,” as defined by an increase in serum creatinine level more than 110% of baseline and by repeated histologic examinations showing AR.
In general,higher levels of Foxp3 mRNA were found in the nonprogressive group as compared with those observed in the progressive group.
(iv) In a retrospective study, Xu et al.:
analysed 125 surveillance biopsies displaying interstitial T-lymphocyte infiltration between nonatrophic tubules in the cortex, 14 with subclinical rejection, 32 with borderline change, and 79 showing interstitial T-lymphocyte infiltration without obvious pathological abnormalities according to Banff criteria.
All previously described cases were classified into two groups: (i) a regulatory phenotype (RP) group, characterized by Foxp3+-infiltrating T lymphocytes in biopsies, and (ii) a cytotoxic phenotype (CP) group, which was dominated by Granzyme B+-T lymphocytes.
No patient of the RP group developed any AR during nearly 5 years of followup, while subjects of the CP group developed biopsy-proven or clinical diagnostic AR within 1 year after biopsy.
(v) Chung et al. investigated the clinical significance of the ratio between IL-17- secreting cells and Treg infiltration in renal allograft tissues with acute T-cell-mediated rejection (ATCMR) on 56 patients with biopsy-proven ATCMR.
The 56 patients were divided into (i) theFoxp3-high group (with Log Foxp3/IL-17 > 0.45) and(ii) theIL-17-high group (with Log Foxp3/IL-17 < 0.45).
The IL-17-high group showed an allograft function significantly decreased as compared with that displayed by the Foxp3-high group, together with higher severity of interstitial and tubular injuries and lower 1-year (54% versus 90%, 𝑃 < 0.05) and 5-year (38% versus 85%, 𝑃 < 0.05) allograft survival rates.
Multivariate analysis revealed that the Foxp3/IL-17 ratio was a significant predictor for allograft outcome.
(vi)D.SanSegundo et al ; using flow cytometry in 90 kidney transplant recipients,analyzed the level of circulating Tregs at peripheral blood level and the association with long-term graft survival.
Patients who maintained high Treg levels (above 70%) at both 6 and 12 months displayed a better long-term graft survival at 4 and 5 years followup.
This mentioned study would suggest that Tregs may play a role in antagonizing the inflammatory state associated with kidney transplantation and may possibly be considered as a prognostic factor of outcome. However, several studies show divergent data potentially contrasting with this vision.
(vii) Veronese et al. analyzed 73 renal transplant biopsies selected for the diagnosis of acute cellular rejection (ACR) type I or type II, acute humoral rejection (AHR), or calcineurin inhibitor toxicity (CNI).
The number of Tregs was found to be significantly higher in ACR type I and type II, as compared with that observed in AHR and CNI toxicity; 96% Foxp3+ cells were CD4+ T lymphocytes aggregated within renal tubules.
However, Kaplan-Meier analysis of 2-year graft survival in patients with ACR type I or type II showed a lower survival rate in patients with higher Foxp3 scores as compared with the other group.
(viii) Bunnag et al.analyzed Foxp3 mRNA expression in 83 renal transplant biopsies for causes linked to histopathology.
Kidneys with T-cell-mediated rejection, antibody-mediated rejection, and mixed rejection showed higher Foxp3 expression as compared with kidneys without rejection.
According to Banff classification, higher Foxp3 expression was associated with higher levels of interstitial inflammation and tubulitis.
In their multivariate analysis, CD4 positivity, and not Foxp3 mRNA expression, was independently associated with graft survival.
(ix)Batsford et al.found no association between Foxp3 T cell expression and graft function one year after transplantation.
However, this study was affected by the reduced number of samples and the choice of excluding patients with a degree of rejection higher than type 1 TCMR.
(x) Dummer et al. have recently observed that intragraft expression of both Foxp3 mRNA and protein was not associated with a better allograft outcome, analysed in terms of graft function and survival at 5 years after transplantation in 96 kidney transplants.
MOHAMMED GAFAR medi913911@gmail.com
3 years ago
Tregs are CD4+CD25 high T lymphocytes expressing FoxP3 transcription factor either constitutively (thymic Tregs or tTregs) or after peripheral recognition of antigens (peripheral Tregs or pTregs).
1-role in self-antigen tolerance 2- suppress inflammatory alloreactive T cells in vitro and in vivo.They 3- inhibit alloreactivity in MLR in vitro and are thought to 4-mediate transplant tolerance elicited via leukocyte costimulation blockade, donor-specific transfusion.
CLINCAL IMPORTANCE OF Treg monitoring in clinical transplantation:
The importance of regulatory T-cells (Treg) in tolerance models makes their surface or intracellular markers obvious candidates to provide a biomarker for transplantation.Unfortunately, a definitive marker for Treg in humans is yet to be found.
Application of cell-based immunotherapy in organ transplantation to minimize the burden of immunosuppressive medication and promote allograft tolerance has expanded significantly over the past decade.
The classic Treg are enriched within the CD4+CD25+ T-cell population. To date, the most reliable marker available is forkhead box p3 (FOXP3), a member of the forkhead
winged helix family of transcription factors. In mice, Foxp3 is a specific marker of Treg , however in humans this transcription factor is also transiently expressed in nonregulatory T-cells upon activation. Other markers used to identify Treg include CD45RB CTLA-4, GITR, CD122, CD103, and galectin-10, and the absence of CD127 can also indicate a regulatory phenotype. A combination of these markers may be the best way of identifying Treg.
Weam Elnazer
3 years ago
Foxp3+ CD4+ T cells are typically analyzed on bioptic samples.
Prognostic validity might be improved by using a graft survival biomarker, which could also be used to monitor immunosuppressive therapy responses.
To diagnose allograft rejection, renal biopsying is an invasive, time-consuming, and sometimes dangerous operation not suitable for everyone. To be sure, this strategy has to be tested on larger cohorts of transplanted patients taking into consideration all the factors discussed above.
For the assessment of Treg function in allograft outcome, it is important to consider the numerous immunosuppressive treatments used and their possible impact on Treg expression and function.
Some immunosuppressive medicines have been shown to increase the amount of Tregs while others reduce their activity.
T-reg function has been demonstrated to be affected by calcineurin inhibitors (CIs), although corticosteroids and rapamycin improved their suppressive efficacy and survival. In organ transplantation, however, it is difficult to distinguish between various immunosuppressants’ effects.
Professor Ahmed Halawa
Admin
3 years ago
Thanks All I just was stressing the importance of Treg in transplant immunology. I want to see more reflection on the paper.
I want to reassure you that we are moving towards clinical transplant immunology based on what we have studied in the past 5 weeks.
Ibrahim Omar
3 years ago
Tregs are a sub-population of lymphocytes and represent 5 % of the total lymphocytic count in the blood. they are of CD4+ type and express 2 major cell surface markers which are CD25 and CTLA-4 (T lymphocyte antigen 4).
Tregs are usually present in the inactive form. however, during inflammatory states, some mediators are released and activate Tregs. of these mediators areTGF-B and IL-12. furthermore, during specific immune reactions on encountering a foreign antigen presented on an antigen presenting cells to CD4+ cells, these CD4+ cells will be activated and undergo differentiation into certain sub-types. of these sub-types, is Tregs. other sub-types are Th1, Th2 and Th17. several transcriptional factors contribute to this differentiation. of these factors are Foxp3, RoR gamma and T-bet.
activated Tregs release some inhibitory cytokines, mainly IL-10 and IL-35. these cytokines do suppression of activated antigen presenting cells, NK cells and T lymphocytes. this will result in some beneficial effects in certain circumstances as self tolerance of microbial flora of the gut and also tolerance of transplanted organs. also, of these beneficial effects, is protection of auto-immunity and development of auto-immune disorders. however, some dangerous effects are also encountered as decreased immune response to tumor cells and so development of some malignancies.
CTLA-4 is also responsible for adequate inhibition of T-cell activation by down-regulation of expression of co-stimulatory molecules CD80 and CD86 on dentritic cells. depletion of CTLA-4 results in spontaneous multi-organ auto-immunity and severe lympho-proliferative disorders.
Tregs can also do depletion of dentritic cells by induction of perforin-dependent cytolysis. this effect is marked at lymph nodes draining tumors.
Tregs have gained a high attraction in managing an early or even a predictive marker of rejection and graft loss. Foxp3 was highly considered and already tested in urine samples and also histopathological samples in many reasonable studies. however benefits are still lacking and waiting larger and high-powered studies.
Hinda Hassan
3 years ago
Regulatory T Cells in the Immunodiagnosis and Outcome of
Kidney Allograft Rejection
T reg are originally a subset of T cells which get activated upon encounter with the antigens. Their role is to suppress the immune destruction role of Tc, APC& NK through IL10 IL35.They have CD25 &CTLA-4. CTLA-4 down -regulate CD80&CD86 on dendretic cells preventing their encounter with CD28 .
There are two types :n Treg(natural) from the thymus and iTreg Tregs(induced;converted from naive t cells peripherally) Principal Mechanisms of T-Cell-Mediated AR:
APC with the antigen will travel to lymphoid tissues where they underwent allorecognition by Tcells. This will result in T cells activation and differentiation into TH1.TH2,TH17 and iTreg. They will return to the graft to induce celluar rejection. Their main site of action is the endothelium of post capillary venules where tethering(through selectin to attach and increase the time of t cell encounter with the endothelium),adhesion to endothelium (through integrin LFA-1) and transmigration( infiltration of t cells into the interstium through gap junctions using diapedesis) .t cells will then destruct the interstisium through metalloproteases. The damage will destruct tubular epithelium and the endothelium and can be mediated :
1-indirectly through Tc cell(cytotoxic CD8+ T) and macropages .(Tc will destruct through perforin, granzyme B, granulolysins & Fas. Macrophages uses TNFα & NO)
2-directly through TNF & INF 𝛾 .
Many studies suggest that T reg are associated with a better response to therapy and lowe risk of graft failure . Treg were investigated through many techniques involving estimation of Foxp3 either in urinary cells , renal tissues and peripheral blood ,or mRNA profile of Foxp3in urine cells or renal tissue . ratio between IL-17- secreting cells and Treg infiltration in renal allograft tissues was also utilized.
On the other hand. Some studies contradict these findings . cases with cellular rejection were found to have higher level of Tregs ,survival rate and allograft outcome are less with higher Foxp3 scores , interstitial inflammation and tubulitis were associated with higher level of Foxp3 .
To overcome these variation in the future, large number of patients need to be enrolled, the need for biopsy samples should be replaced by non invasive markers and a universal protocol to avoid the effect of different immunosuppressive on Treg expression and function.
Ban Mezher
3 years ago
CMR process start when APC presented donor Ag to HLA I& II molecule, this will activate response against allograft causing activation of naive T cells which can differentiate into special subsets( destructive as CD4 & CD8, protective as Treg). So balance between protective & destructive T cells is very important for graft outcome.
Acute rejection can result from both cellular & Ab mediated immunity, & there are different types of cells participate in rejection as T cells, B cells, macrophages, plasma cells, eosinophils & neutrophils, but T cells are the central key in regulation of immune response. CD4 T cells can causing graft injury indirectly by activation of CD8 T cells & macrophages or/& directly through production of TNF & INF-gama.
Reg Cells are derived from CD4T cells ( with expression of CD25 & CTL4-A) , it secret inhibitory cytokines as IL-10 & IL-35 that have important role in controlling the function of T cells, NK & APC. T cells subsets have several transcription factors include Foxp2, RORyt, T bet & GATA3, these factors activate genes that can control T cell function. IL10 ( secreted by Treg) can inhibit the activity of effector T cells in infection, autoimmunity & cancer, while CTL4-A that expressed on Treg can inhibit expression co-stimulatory molecule CD80 & CD86 on DC leading to impaired CD28 & inhibit T cell function. In summary DC can be controlled by different mechanisms resulting in T cell inhibition & promoting of functional tolerance.
Several studies show that presence of Foxp3 & Foxp3 expression in transplanted kidney & urine in patients with acute rejection associated with good response to steroids & reversal of rejection & subsequent better graft survival. The result of other studies show no association between Foxp3 expression & better graft outcome.
Mohamad Habli
3 years ago
Acute rejection is responsible for up to 12% of graft loss with the highest risk generally occurring during the first six months after transplantation. AR is classified into humoral and cellular rejections.
Recognition of donor allograft by recipient T lymphocyte results in activation of naive T cells that differentiate into subsets including cytotoxic CD8+ and helper CD4+ T cells type 1 (TH1) and TH2 cells or into regulatory T cells.
The immune reaction directed against a renal allograft has been suggested to be characterized by two major components: a destructive one mediated by CD4+ helper and CD8+ cytotoxic T cells and a protective response mediated by Tregs. Many studies have been performed in order to define the role of Tregs either in the immunodiagnosis of transplant rejection or as predictor of the clinical outcomeRegulatory T cells(Tregs) are a subset of CD4+ T cells. Tregs produced by a normal thymus are termed ‘natural’; nTreg. Treg formed by differentiation of naïve T cells outside the thymus, i.e. the periphery, or in cell culture are called ‘adaptive’ or inducible ; iTreg.
Natural Treg are characterised as expressing both the CD4 T cell co-receptor and CD25, which is a component of the IL-2 receptor. Treg are thus CD4+ CD25+. Expression of the nuclear transcription factor Forkhead box P3 (FoxP3) the determines natural Treg development and function. FoxP3 is essential for maintaining suppression of the immune system.
Regulatory suppressive mechanisms of T reg
Direct mechanisms by secreting cytokines such as IL-10, TGFβ and IL-35 and producing granzyme and perforin, leading to apoptosis or inhibition of effector cells
Indirect mechanisms b expression of CD39/CD73, which depletes the microenvironment of extracellular ATP via the generation of adenosine and AMP, molecules with implicated in immunosuppressive effects
They can sequester, by the high expression of CD25, IL-2, reducing effector T cells proliferation and differentiation
IL-2 starvation reduces NKs from proliferating and exhibiting effector functions
Some studies showed that higher urinary level of FoxP3 was associated with better response to corticosteroids, less rise in serum creatinine and better allograft outcome.
In a retrospective study evaluating protocol biopsies demonstrated that biopsy infiltrated with T reg (FoxP3+T lymphocytes) did not show any form of AR during 5 y period after biopsy while those infiltrated with cytotoxic T cells (Granzyme B+T lymphocytes) developed AR within 1 year after biopsy.
A study evaluating the correlation between ATCMR and the Tregs/Th17 ratio in the biopsy, found that graft rejection is associated with lower ratio.
Higher serum Treg is correlated with better graft survival. The level of peripheral circulating Treg was associated with better graft survival, patients with peripheral Treg of > 70% at 6, 12 m after transplantation are associated with better graft survival at 5 years.
Other studies demonstrated severity of kidney damage in the presence of Treg. Urinary FoxP3 was found to be higher in patients with acute rejection comparing to than patients without AR. In kidney biopsies for patients with acute rejection, higher number of Treg cells and FoxP3 was associated with more interstitial inflammation, tubulitis and lower graft survival
Doaa Elwasly
3 years ago
The immune reaction involved in the renal allograft is elicited by two major arms a destructive one mediated by CD4+ helper and CD8+ cytotoxic T cells and a defensive one mediated by Tregs.
Allograft rejection starts when the recipient’s T cells recognize the donor antigen on Antigen presenting cells , leads to T cell activation followed by differentiation.
Tregs was assed if possible to be used as possible biomarker of acute kidney transplant rejection and/or prognostic factor related to the graft survival
T reg induces tolerance by preventing the activation of autoreactive immune responses,
T reg represent a CD4+ T cell subpopulation expressing CD25 molecule and “cytotoxic T-lymphocyte antigen 4” (CTLA-4) suppressing the activation of T lymphocyte , APC ,NK cells .
Tregs produce IL-10, which inhibits, effector T cell activity during infection, autoimmunity, and cancer while CTLA-4 loss can cause severe lymphoproliferative disease and multiorgan autoimmunity.
Tregs can control Denderitic cell activity by multiplepathways , leading to inhibition of effector T cell and enhancing functional tolerance.
A study demonstrated that the levels of Foxp3 transcripts, as a specific marker of Tregs in cells obtained from urine samples of patients with AR were higher as compared with those in other groups analyzed; opposing expectations, this was justified by assuming that cells infiltrating the graft include both graft-destructive cells such as cytotoxic T cells and graft-protective Foxp3-expressing Tregs.
Another study concluded that combination of Foxp3 transcripts and creatinine levels together proved to be a better prognostic marker of rejection reversal then each one separately .
It was demonstrated that patients who displayed rejection and higher levels of urinary Foxp3 showed better response to steroid treatment with lower risk for graft failure in comparison to those with lower levels of Foxp3.
Multivariate analysis revealed that the Foxp3/IL-17 ratio was an important predictor for allograft outcome.
Authors published that high Treg levels at both 6 and 12 months revealed a better long-term graft survival at 4 and 5 years suggesting that Tregs can play a role in opposing the inflammatory state associated with kidney transplantation and can be considered as a prognostic marker.
Shereen Yousef
3 years ago
Acute rejection is either humoral or cell mediated and It is responsible for 12% graft loss within the first 6 months.
Cellular rejection occurs when , APCs ptesents donor alloantigens through class I or class II HLA molecules, to naive T cells to initiate immune response, resulting in activation of naive T cells that differentiate into subsets including cytotoxic CD8+ and helper CD4+ T cells type 1 (TH1) and TH2 cells or into cytoprotective immunoregulatory T cells (Tregs).
several transactions factors contribute to the functional specification of this subsets including Foxp3, ROR𝛾t, T-bet, and GATA3, which activate genes involved on the control of T cell function.
immune reaction is either destructive mediated by CD4+ helper and CD8+ cytotoxic T cells or a protective mediated by T reg cells .
balanc between these two opposite responses affect the graft survival.
Treg and Tolerance
Regulatory T (Treg) cells are a subset of CD4+ T cells that is involved in maintaining immune homeostasis and self-tolerance by inhibiting the pro-inflammatory activities of CD4+ and CD8+ effector T cells, natural killer cells, and antigen-presenting cells.
It is either thymus derived( tTregs) or peripheral derived (pTregs) from the peripheral conversion of naïve CD4+ T cell
T reg cells Characterized by expression of CD4, CD25, FOXP3 (CD4+CD25+FoxP3+) and CTLA-4
Inflammatory cytokines like IL-10, TGF-β, and IL-2 have important role in maintenance of suppressive activity/function of Treg.
CTLA-4 cause defective co stimulation via CD28 through downregulation of expression of CD80 and CD86 on dendritic cells of lymphoid tissues
They can also induce perforin-dependent cytolysis of dendritic cells In tumor draining lymph nodes
loss of CTLA-4 in Ttreg cells lead to the development of severe lymphoproliferative and autoimmune disease.
Regulatory T Cells in the Immunodiagnosis and Outcome of Kidney Allograft Rejection
Number of studies have demonstrated the importance of T reg in inducing tolerance and improving graft survival
One of most important studies was based on the measurement of FOXP3 in urine sample of transplant patients and found that FOXP3 level was high in patients with acute rejection & a combination of FOXP3 transcripts and creatinine level proved to be better prognosticators of rejection reversal than FOXP3 or creatinine alone.
Patients who displayed acute rejection and high level of FOXP3 showed better response to steroids and lower risk of graft failure.
And another study showed that level of peripheral circulating Treg detected by FCM is correlated to graft survival, patients with peripheral Treg of > 70% at 6, 12 m after transplantation are associated with better graft survival at 5 years.
Although some studies didn’t show the same results and it was found that patients with acute rejection higher number of Treg cels and Foxp 3 score in biopsy are associated with more interstitial inflammation, tubulitis and lower graft survival.
The role of immunosuppressive drugs on number and function of Tregs is important as some studies showed that steroids and rapamycin improved its functions while CNI decreased its number and functions
Huda Al-Taee
3 years ago
Tregs represents 5% of total lymphocytes in the blood.
Tregs are essential for developing tolerance and this role has been demonstrated in tolerated skin allografts.
Many studies has been done to evaluate the role of Tregs in renal transplantation, one of the most important studies was based on the measurement of FOXP3 in urine sample of transplant patients and found that FOXP3 level was high in patients with acute rejection & a combination of FOXP3 transcripts and creatinine level proved to be better prognosticators of rejection reversal than FOXP3 or creatinine alone. Patients who displayed acute rejection and high level of FOXP3 showed better response to steroids and lower risk of graft failure.
Another study compared the level of FOXP3 to some molecules that are expressed by the cytolytic attack to the graft and found that FOXP3 level was higher in patients with rejection than those with acute tubular necrosis.
Another study found that urinary cell mRNA profiles for FOXP3 and other molecules were able to associate with an early steroid withdrawal regimen with ATG induction with excellent graft and patient outcomes in HIV infected recipients of kidney transplantation.
Another study to described the relation between FOXP3 level and disease progression in patients with boarderline rejection and found that higher level of FOXP3 found in non progressive disease.
Another study demonstrated the relation between the type of T cells infiltrating the graft( regulatory or cytotoxic) and the development of rejection and found that no patient with Tregs infiltration developed acute rejection during 5 years of follow up.
Multivariate analysis showed that the FOXP3/IL-17 ratio was a significant predictor of allograft outcome.
patients who maintained high level Tregs at 6&12 months displayed a better long term graft survival.
The number of Tregs was found to be significantly higher in acute TCM rejection type I&II as compared to ABMR and CNI toxicity however lower survival rate in patients with higher FOXP3.
kidneys with acute TCM rejection, ABMR and mixed rejection showed higher FOXP3 level as compared to kidneys without rejection.
higher expression of FOXP3 was associated with high level of inflammation and tubulitis.
Riham Marzouk
3 years ago
Stimulation of T cell (naiive CD4) upon exposure to antigen, it will differentiate into many subsets different in function, T cell CD4 which express CD25 and CTLA-4 (cytotoxic T lymphocyte antigen 4 ) and has transcription factor Fox3p is called Treg (induced Treg iTreg).
There is also nTreg, which is natural Treg originate from thymus directly.
Treg is very important to maintain T cell homeostasis and control immune response, especially for self-antigens.
Treg represent 5% from circulating T lymphocytes and responsiple for peripheral tolerance , and it is recruited at mucosal surface when exposed to antigen there and also when exposed to self antigens.
Inflammatory cytokines like IL-10, TGF-β, and IL-2 have important role in maintenance of suppressive activity/function of Treg.
Treg produce IL-10 which inhibits T cell activation in cancer, autoimmune condition and infection.
Expression of CTLA-4 on Treg cells can impair co-stimulation pathway through CD28/CD86 on APCs, so impair T cell activation.
Treg can contact DC (dendritic cell) and induce its lysis and this will inhibit T cell activation and promote tolerance.
Graft biopsy is invasive procedure, and is operator dependent , so we should search for another marker or indicator to diagnose acute rejection as Treg or Fox3p level in the urine, but still need a lot of studies and research to reach the goal.
Sherif Yusuf
3 years ago
Immune response to allograft begins when donor antigens are carried out in complexes with HLA class I, II by APCS (immature dendritic cells) which then migrate to lymph node and spleen where they become mature, Mature APCS present antigen (either intact in case of donor APCS or processed in case of recipient APCS) to naïve T cells which differentiate into
1- CD4+ T helper which activate B cells, macrophages (delayed type hypersensitivity), CD8+ T cells, and produce inflammatory cytokines like TNF and IFN-𝛾 that cause direct injury to the graft.
2- CD8+ cytotoxic t cells with subsequent cell mediated cytotoxicity
3- T regulatory cells that suppress immune system
T regulatory (Treg) cells are a subclass of CD4 T cells that is responsible for suppression of immune response
It constitute 5% of CD4 positive T cell population
Characterized by expression of CD4, CD25, FOXP3 (CD4+CD25+FoxP3+)
It is either thymus derived( tTregs) or peripheral derived (pTregs) from the peripheral conversion of naïve CD4+ T cells
Transformation of naive CD4+ T cell to pTreg occur due to repeated stimulation to non- self antigen or exposure to certain cytokines (IL10, TGF-β)
Treg is important in initiating and maintaining peripheral tolerance as they suppress immune response by the following mechanisms :
A- Contact inhibition through surface expression of CTLA-4 medicated by Foxp 3
⦁ CTLA-4 cause defective co stimulation via CD28 through downregulation of expression of CD80 and CD86 on dendritic cells of lymphoid tissues
⦁ It was found that loss of CTLA-4 in Ttreg cells lead to the development of severe lymphoproliferative and autoimmune disease.
⦁ Tregs can also induce
B- Contact perforin-dependent cytolysis of dendritic cells
⦁ In tumor draining lymph nodes cytolysis of DCS occur under the effect of Treg
C- Non contact inhibition through the release of IL10 , TGF-β
⦁ It was found that selective deletion of IL10 in Tregs lead to the development of spontaneous colitis with marked skin and lung immune responses
The net result is :
⦁ Suppression CD4 T cell
⦁ Suppression of CD8+ T cells
⦁ May suppress B cells and dendritic cells
Several studies demonstrated beneficial effect of Treg cells in kidney allograft rejection
⦁ In patients with acute rejection the higher the urinary level of Foxp 3 the better is the response to corticosteroids, the less is the rise of serum creatinine and and the better is the outcome
⦁ In a retrospective study involving protocol biopsies which demonstrate no significant pathology based on Banff classification, biopsies were either infiltrated mainly by T reg (Foxp3+Tlymphocytes) or by cytotoxic T cells (Granzyme B+T lymphocytes). regulatory phenotype group did not show any form of AR during 5 y period after biopsy while cytotoxic phenotype group developed AR within 1 year after biopsy
⦁ A study addressing the relation between ATCMR and the Tregs/Th17 ratio in the biopsy of these patients found that graft rejection is associated with lower ratio
⦁ The level of peripheral circulating Treg detected by FCM is correlated to graft survival, patients with peripheral Treg of > 70% at 6, 12 m after transplantation are associated with better graft survival at 5 years
Other studies failed to demonstrated beneficial effect of Treg in kidney allograft rejection
⦁ In patients with acute rejection the level of urinary Foxp 3 was found to be higher than patients without AR
⦁ In patients with acute rejection the level of urinary Foxp 3 was found to be higher than patients without AR,
⦁ In patients with acute rejection higher number of Treg cels and Foxp 3 score in biopsy are associated with more interstitial inflammation, tubulitis and lower graft survival
An important part in this paper is this paragraph;
Recent clinical studies have demonstrated how different immunosuppressive drugs can influence differently the number and function of Tregs, by inducing stimulation, inhibition, or even noninterference. In particular, while corticosteroids and rapamycin have been shown to improve the suppressive activity and survival of Tregs, other treatments as calcineurin inhibitors (CIs) have been shown to affect Treg function
it’s difficult to differentiate the effect of different immunosuppressant from each other
one of the immunosuppressant may have an adverse effect or negative impact on the outcome of transplant in specific issues, but overall having positive impact and good outcome.CNIs although having negative impact on maintenance of tolerance but the overall outcome of transplant is good with CNIs.
what is needed is a special agent that target Treg and potentiate it’s capability of inducing and maintaining tolerance without compromizing the stability of immunological balance.
Role of Treg in transplant
1) play a role in the maintenance of T Cell homeostasis under different conditions, inhibit effector T cell activation and promoting functional tolerance to allogenic graft.
2)by preventing activation of auto reactive immune response contribute to maintaining self tolerance.
3)T regs produce IL-10 which inhibits directly or indirectly effector T cell activity during autoimmunity.
4) CTLA4 expressing Tregs downregulate the expression of costimulatory molecules CD80 and CD86 on APCs.
5) Tregs may play a role in antagonizing the inflammatory state associated with kidney transplantation and may possibly be considered as a prognostic factor of outcome.
6)Patients who maintained high Treg levels (above 70%) at both 6 and 12 months displayed a better long-term graft survival at 4 and 5 years followup.
7)corticosteroids and rapamycin improve the suppressive activity and survival of Tregs,calcineurin inhibitors (CIs) have affect Treg function.
The analysis of some of the most important recent studies dealing with Tregs used as possible biomarker of acute kidney transplant rejection and/or prognostic factor related to the graft survival (see Table 1) inspires some critical observations. First of all it must be pointed out that most of the times the final assessment of the studies is affected by the modest statistical validity of the analyzed sample due to the small
number of patients included. The consideration that analysis of Foxp3 mRNA and Foxp3+ CD4+ T cells is often performed on bioptic samples
is a critical element to take into account. The use of a graft survival biomarker could be able to improve the prognostic validity of the procedure, also in terms of evaluation of response to immunosuppressive therapies. On the other
hand, it must be considered that renal biopsying for the diagnosing of allograft rejection is an invasive and timeconsuming procedure with some risk of complications and not easily manageable for all patients. Therefore, in the
general followup of transplanted patients, a noninvasive test could be more advantageous, although this option still needs to be confirmed on additional cohorts taking into account all
the aspects considered earlier. Lastly, the different immunosuppressive therapies employed in the available studies and the potential effects on Treg expression and function constitute another critical variable to take into account in the evaluation of Treg function in the allograft outcome. Recent clinical studies have
demonstrated how different immunosuppressive drugs can influence differently the number and function of Tregs, by inducing stimulation, inhibition, or even noninterference. In particular, while corticosteroids and rapamycin have been
shown to improve the suppressive activity and survival of Tregs, other treatments as calcineurin inhibitors (CIs) have been shown to affect Treg function [56]. However, it is difficult to differentiate the effects of different immunosuppressants, although the use of selective pharmacological
treatments able to regulate the suppressive function of Tregs would be attractive in organ transplantation.
Acute rejection (AR) is responsible for up to 12% of graft loss with the highest risk
generally occurring during the first six months after transplantation. AR may be broadly
classified into humoral as well as cellular rejection. Cellular rejection develops when
donor alloantigens, presented by antigen-presenting cells (APCs) through class I or
class II HLA molecules, activate the immune response against the allograft, resulting in
activation of naive T cells that differentiate into subsets including cytotoxic CD8+ and
helper CD4+ T cells type 1 (TH1) and TH2 cells or into cytoprotective immunoregulatory
T cells (Tregs). The immune reaction directed against a renal allograft has been
suggested to be characterized by two major components: a destructive one, mediated by
CD4+ helper and CD8+ cytotoxic T cells, and a protective response, mediated by Tregs.
The balance between these two opposite immune responses can significantly affect the
graft survival. Many studies have been performed in order to define the role of Tregs
either in the immunodiagnosis of transplant rejection or as predictor of the clinical
outcome. However, information available from the literature shows a contradictory
picture that deserves further investigation. .
Please summarise the different roles of T reg in transplantation.
Acute rejection is classified into Antibody mediated ( humoral) and cellular rejection.
Cscade of Cellular rejection starts when APC s present Donors Ag (HLA class I and II) to recipients T lymphocytes resulting in activation of naive T cells that differentiate into subsets including cytotoxic CD8+ and helper CD4+ T cells type 1 (TH1) and TH2 cells or into cytoprotective immunoregulatory T cells (Tregs). (5)
CD4 + and CD8+ are considered the destructive arm of Alloimmune response against the graft, They infiltrate into the transplanted kidney, where they release cytokines and chemokines, causing cell death either directly or indirectly [6]. However T reg cells are the protective arm. The balance between both opposite immuneresponses can significantly affect the graft survival [7].
Tregs were identified as a CD4+ Tcell subpopulation expressing CD25 [14]and cytotoxic T-lymphocyte antigen 4” (CTLA-4)
Originate mainly from the thymus (natural, nTregs) and from the peripheral conversion of naive CD4+ Tcells under appropriate stimulus conditions (induced, iTregs) ( 20].
Treg cells prevent the activation of autoreactive immune responses , induce and mentain tolerance , contribute to maintaining homeostasis of the microbial flora of the gut, and promote the immunogenic escape of cancer cells [11].
Activation pf Treg cells occur after exposure inflamed tissues where the local cytokine In particular TGF-𝛽,IL-10,andIL-2 or play a role in their activation and regulation , or by exposure to environmental conditions such as those produced by tumors [28].
Tregs can control DC activity by multiple mechanisms, and this results in the inhibition of effector T cell activation and promoting of functional tolerance.
Tregs produce IL-10, which is able to inhibit, either directly or indirectly, effector T cell activity during infection, autoimmunity, and cancer [30].
On the other hand Tregs expressing CTLA-4 down regulate the expression of the costimulatory molecules CD80 and CD86 on DC ending in impaired costimulation via CD28 and defective T cell stimulation. [42].
Tregs can also induce perforin-dependent cytolysis of DCs in tumour-draining lymph nodes [45].
Many studies found that higher peripheral Treg levels in blood was associated with better graft survival and outcome, hence it could be used as a prognostic factor assessing and predicting graft outcome
References:
(5) S.Schaub,J.A.Wilkins,D.Rush,andP.Nickerson,“Developing a tool for noninvasive monitoring of renal allografts,” Expert Review of Proteomics,vol.3,no.5,pp.497–509,2006.
[6] B. J. Nankivell and S. I. Alexander, “Rejection of the kidney allograft,” The New England Journal of Medicine,vol.363,no. 15, pp. 1451–1462, 2010.
[7]X.X.Zheng,A.S´anchez-Fueyo,M.Sho,C.Domenig,M.H. Sayegh, andT.B.Strom,“Favorablytippingthebalancebetween cytopathic and regulatory T cells to create transplantation tolerance,” Immunity,vol.19,no.4,pp.503–514,2003.
(11) S. Sakaguchi, T. Yamaguchi, T. Nomura, and M. Ono, “Regulatory T cells and immune tolerance,” Cell,vol.133,no.5,pp. 775–787, 2008.
(14) S. Sakaguchi, N. Sakaguchi, M. Asano, M. Itoh, and M. Toda, “Immunologic self-tolerance maintained by activated T cells expressing IL-2 receptor 𝛼-chains (CD25): breakdown of a single mechanismofself-tolerance causes various autoimmune diseases,” Journal of Immunology, vol. 155, no. 3, pp. 1151–1164, 1995.
(20) M. O. Li, S. Sanjabi, and R. Flavell, “Transforming growth factor-𝛽 controls development, homeostasis, and tolerance of T cells by regulatory T cell-dependent and -independent mechanisms,” Immunity,vol.25,no.3,pp.455–471,2006.
28] M. D. Sharma, B. Baban, P. Chandler et al., “Plasmacytoid dendritic cells from mouse tumor-draining lymph nodes directly activate matureTregsviaindoleamine2,3-dioxygenase,”Journal of Clinical Investigation,vol.117,no.9,pp.2570–2582,2007.
[30] K. Loser, J. Apelt, M. Voskort et al., “IL-10 controls ultravioletinduced carcinogenesis in mice,” Journal of Immunology,vol. 179, no. 1, pp. 365–371, 2007.
[42] O.S.Qureshi,Y.Zheng,K.Nakamuraetal.,“Trans-endocytosis of CD80 and CD86: A molecular basis for the cell-extrinsic function of CTLA-4,” Science,vol.332,no.6029,pp.600–603, 2011.
[45] A. Boissonnas, A. Scholer-Dahirel, V. Simon-Blancal et al., “Foxp3+ Tcells induce perforin-dependent dendritic cell death in tumor-draining lymph nodes,” Immunity,vol.32,no.2,pp. 266–278, 2010.
Please summarise the different roles of Treg in transplantation.
Regulatory T cells (Treg) are CD4 positive T cells which express CD25 and CTLA4 with low CD127. In aadition, they are positive for demethylated FOXP3. They comprise approximately 5% of total lymphocytes in blood and are very important for tolerance.
Treg may be either natural (nTreg) or induced (iTreg) which remain dormant and get activated by inflammation (through TGF beta, Interleukin 10 and Interleukin 2), malignancy and T Cell receptor (TCR) engagement inhibiting effector T cell activation causing tolerance or helper response.
Treg may also be classified as
a) Naive (resting) Treg cells (FOXP3+ CD45RA+),
b) activated (effector) Treg cells (FOXP3+++ CD45RA-) and
c) FOXP3+ effector (cytokine producing) cells (FOXP3+ CD45RA-): which release proinflammatory cytokines liken IL-2, IL-17, Interferon gamma and have no immunosuppressive function.
Treg release IL-10 inhibiting effector T cell activity associated with infection, autoimmunity and cancers. Through CTLA-4, Treg inhibit co-stimulation on dendritic cells and cause perforin dependent dendritic cell lysis.
Increased urinary FOXP3 in transplant recipients with acute rejection has been shown to be associated with more responsiveness to steroids and decreased rates of graft failure.
In a study involving protocol biopsies, interstitial T lymphocyte infiltration was associated with no acute rejection episodes if it was FOXP3 positive while those with Granzyme B positivity developed acute rejection within one year. Patients with increased circulating Treg levels have been shown to be associated with better graft survival. It has been shown that steroids and mTOR inhibitors increase Treg survival while CNI affect Treg function.
TRACT trial, conducted in US was performed in living kidney transplant recipients receiving Alemtuzumab induction with MMF and Tacrolimus which was converted to sirolimus at day 30 and Treg infusion at day 60. It showed no opportunistic infection and no episode of acute rejection at 2 years in all the patients. (1)
TASK trial, conducted in UK, was performed in patients with subclinical inflammation on 6 month protocol biopsies (Banff i & t <2) showed no inflammation and graft dysfunction at 12 months, after receiving Treg infusion. (1)
Reference:
1) Atif M, Conti F, Gorochov G, et al. Regulatory T cells in solid organ transplantation. Clin Transl Immunology 2020;9:e1099
T reg is crucial for peripheral tolerance.
they are concerned with suppression of immune response.
Principal Mechanisms of T-Cell-Mediated AR
Transplant rejection is the consequence of the recipient’s alloimmune response and consists of manifested deterioration or complete function loss of the transplanted organ
AR classified into humoral and cellular rejections
Different cell types are involved in the graft rejection including T and B cells, macrophages, plasma cells, eosinophils, and neutrophils.,
T cells play a crucial role either in mounting and/or regulating alloreactive responses. T he main targets of cell-mediated damage are the tubular epithelium and the endothelium.
acute allograft rejection starts when the recipient’s T cells recognize the donor alloantigens presented by APCs
T cell infiltration into the graft is mainly at the level of postcapillaryvenuleendothelium.Threemainstepscanbe identified: tethering, adhesion, and transmigration[
Treg and Tolerance
Tregs play a critical role in the maintenance of T cell homeostasis under different immune conditions.
Origin of Tregs. Tregs were identified as a CD4+ Tcell subpopulation expressing CD25 moleculeand“cytotoxic T-lymphocyte antigen 4” (CTLA-4) at a similar extent to that displayed by activated T cells [15, 16].
The presence of CTLA4 and the release of inhibitory cytokines including IL-10 and IL-35 suggestedasuppressorphenotypeforthesecells andcriticalroleincontrollingtheactivationandfunctionof Tlymphocytes as well as of APC and NK cells.
Circulating Pool and Activation of Tregs
Tregs are essential for maintaining peripheral tolerance; nevertheless, they show a quiescent phenotype when isolated from a noninflammatory environment and require functional activation fortheacquisitionofTregfullfunctionalsuppressiveactivity ]thatcanbeachievedfollowingexposuretoself-antigens or to antigens presented at mucosal surfaces where they can be recruited. Tregs can also be functionally activated while migrating through inflamed tissues, or by exposure to environmental conditions such as those produced by tumors
Regulation of Immune Responses by Tregs
Tregs produce IL-10, which is able to inhibit, either directly or indirectly, effector T cell activity during infection, autoimmunity, and cancer
Regulation of immune functions mediated by CTLA-4expressing Tregs depends on the ability of CTLA-4 molecule to downregulate the expression of costimulatory molecules CD80andCD86ondendriticcells(DCs)oflymphoidtissues resulting in impaired costimulation via CD28 and defective Tcell stimulation
Regulatory T Cells in the Immunodiagnosis and Outcome of Kidney Allograft Rejection
T he consideration that analysis of Foxp3 mRNA and Foxp3+ CD4+ T cells is often performed on bioptic samples is a critical element to take into account. The use of a graft survival biomarker could be able to improve the prognostic validity of the procedure, also in terms of evaluation of response to immunosuppressive therapies.
Role in T reg cells
They balance ;through their protective effect ,the destructive effect played by other T cells.
they are subset of CD+ cells and they inhibit pro inflammatory activities of CD4+and CD8+ effector cells , NK cells and APCs .They express CD4,CD25,FOXP3and CTLA-4.
Suppressive T reg activity maintenance is related to inflammatory cytokines like IL-2 &10 and TGF-B.CTLA-4 combats co stimulation targeting CD28 via downregulation of CD80 and 86 expression .Loss of CTLAw-4 in T reg cells leads to severe lymphoproliferative and autoimmune disease. T reg cells have important role in improving graft survival and evolving tolerance .High level of FOXP3 was associated with favorable response to steroids and lower risk of graft failure in patients with acute rejection .It was found that level of circulating T reg is correlated to graft survival ;when more than 70%at 6 and 12 months after Tx are associated with better graft survival at 5 years.
Steroids and rapamycin were found to improve T reg functions. On the other hand, CNI decreased number and function of T reg cells.
Role of T reg in transplantation
Treg is an important component of the immune system and it represent the beneficial arm of immune response .it represents about 5% of total lymphocytes and plays key role in maintenance of T cells homeostasis :
It controls the activation and function of T cells, APCs, & NK cells as well as Control of immune responses in lymphoid and non-lymphoid tissue.
Produces IL-10 ; the inhibitor of the effector T cells activity during infection, auto-immunity, and cancer The CTLA-4 expressing Treg down regulate the expression of co-stimulation molecules in CD80 and CD86 on Dendritic cells resulting in dysfunctional co-stimulation via CD 28 .They induce perforin-dependent cytolysis of the Dendritic cells in tumour-draining lymph node. High levels of FOXP3 are associated with high levels of interstitial inflammation & tubulitis.T reg is opposing the inflammatory states associated with kidney transplantation and this may be considered as a prognostic factor of graft outcome.
T reg is subpopulation of CD4 T helper cells, it represent 5% of circulating T lymphocytes, orignate from the thymus,it has Immun protective effect as the regulatory mechanism . It express CD25 and released IL-10 and CTL-A4 , work by many transcripter like grazymes and FOXP3 to suppress T cells in autoimmune disease and cancers.
The follow up and measurement of those molecules will give a clue about graft status, survival and possibility of Acute or chronic rejection either T cell mediated rejection or antibodies mediated rejection. They contribute to maintain peripheral tolerance.
There are two types of Tregs: one which originate from thymus ( nTregs) and the other one by stimulus from CD4+ T cells (iTregs). Tregs are subtypes of CD4+ T cell that express CD 25 and CTLA-4 and release IL-10 and IL-35 and have suppressor effects for T cells, APC and NK cells. FOXP3 transcription factor causes transforming from naive T cell CD4 + to iTregs. TGF-β, IL10 and IL-2 contribute in function of Tregs. CTLA-4 expressing Tregs down-regulate CD80 costimulatory on DCs. Tregs can induce tolerance to graft. FOXP3 expression could be transient during T cell activation. So these cells can differentiate into cytotoxic cells that have an active role in rejection or into Tregs with regulatory function. Foxp3/IL-17 ratio could be a predictor marker for TX outcome. This idea is attractive but needs more investigation to use these makers. Corticosteroid and rapamycin improve function of Tregs but CNIs can suppress Tregs.
-Acute rejection (AR) is responsible for up to 12 % of graft loss commonly within the first 6 months after transplantation.AR can be classified into humoral and cellular rejection.
-Cellular rejection develop when donor alloantigen, presented by an antigen-presenting cell (APCs) through class I or class II HLA molecules, activate an immune response against the allograft, resulting in activation of naïve T cell which differentiates into cytotoxic CD8+ and helper CD4+cells (TH1) and TH2 or cytoprotective immunoregulatory T cell (Tregs), also Tregs cell originate from the thymus gland.
-Tregs in CD4+T cell expressing CD25 and T lymphocyte antigen 4 (CTLA-4).
-Treg cells are about 5% of T lymphocytes.
-Tregs maintain T cell homeostasis
-prevent activation of autoreactive immune response
-contribute to maintaining self-tolerance and homeostasis of the microbial gut flora
-promote the immunogenic escape of cancer cells.
-Tregs produce IL- 10 which inhibit, either directly or indirectly effector T cells during infection, autoimmunity, and cancer.
-CTLA-4 –expressing Tregs can down-regulate the expression of costimulatory molecules CD80 and CD86 on dendritic cells of lymphoid tissues resulting in impaired co stimulation via CD 28 and defective T cell stimulation.
-Treg cells can inhibit dendritic cells(DC) by stable Treg-DC contact lead to Tregs- mediated inhibition and also Tregs can induce perforin-dependent cytolysis of DC.
-Foxp3 in the urine analysis was high in patients with acute rejection and associated with better response to steroids and lower risk for graft failure.
-Multivariate analysis revealed that Foxp3/IL-17 ratio was a significant predictor for allograft outcome.
-Patients who maintain high Treg levels at both 6 and 12months display better long-term graft survival at 4qnd 5 years follow up.
-According to Banff classification, higher Foxp3 expression was associated with higher levels of interstitial inflammation and tubulitis.
–
The immune reaction directed against a renal allograft has been suggested to be characterized by two major components: a destructive one, mediated by CD4+ helper and CD8+ cytotoxic T cells, and a protective response, mediated by Tregs. The balance between these two opposite immune responses can significantly affect the graft survival.
Antibody-mediated rejection is characterized by the presence of an antibody infiltration into the transplanted kidney, targeting HLA antigens on the peritubular and glomerular capillary endothelia, which results in complement activation, cytokine and chemokine release, and induction of adhesion molecules.
Cellular rejection develops when donor alloantigens, presented by antigen-presenting cells (APCs) through class I or class II HLA molecules, activate the immune response against the allograft, resulting in activation of naive T cells that differentiate into subsets including
cytotoxic CD8+ and helper CD4+ T cells type 1 (TH1) and TH2 cells or into cytoprotective immunoregulatory T cells (Tregs). CD4+ and CD8+ T cells infiltrate into the transplanted kidney, where they release cytokines and chemokines, causing cell death either directly or indirectly.
Different cell types are involved in the graft rejection including T and B cells, macrophages, plasma cells, eosinophils, and neutrophils. T cells play a crucial role either in mounting and/or regulating alloreactive responses.
T cell infiltration into the graft is mainly at the level of postcapillary venule endothelium. Three main steps can be identified: tethering, adhesion, and transmigration.
Treg and Tolerance
Tregs play a critical role in the maintenance of T cell homeostasis under different immune conditions. They prevent the activation of autoreactive immune responses, contribute to
maintaining self-tolerance and homeostasis of the microbial flora of the gut, and promote the immunogenic escape of cancer cells.
Origin of Tregs: Tregs were identified as a CD4+ T cell subpopulation expressing CD25 molecule and “cytotoxic T-lymphocyte antigen 4” (CTLA-4) at a similar extent to that
displayed by activated T cells. The presence of CTLA-4 and the release of inhibitory cytokines including IL-10 and IL-35 suggested a suppressor phenotype for these cells and critical role in controlling the activation and function of T lymphocytes as well as of APC and NK cells.
Tregs originate mainly from the thymus (natural, nTregs) and from the peripheral conversion of naive CD4+ T cells under appropriate stimulus conditions (induced, iTregs)
Circulating Pool and Activation of Tregs. Circulating Tregs represent 5% of total lymphocytes in blood. Tregs are essential for maintaining peripheral tolerance; nevertheless,
they show a quiescent phenotype when isolated from a noninflammatory environment and require functional activation for the acquisition of Treg full functional suppressive activity that can be achieved following exposure to self-antigens or to antigens presented at mucosal surfaces where they can be recruited. Inflammation plays an important role in driving the local
cytokine milieu. In particular TGF-𝛽, IL-10, and IL-2 have been shown to be critical in regulating activation and/or maintenance of the immunosuppressive functions of Tregs
Regulation of Immune Responses by Tregs.
Tregs produce IL-10, which is able to inhibit, either directly or indirectly, effector T cell activity during infection, autoimmunity, and cancer.
Regulation of immune functions mediated by CTLA-4- expressing Tregs depends on the ability of CTLA-4 molecule to downregulate the expression of costimulatory molecules CD80 and CD86 on dendritic cells (DCs) of lymphoid tissues resulting in impaired costimulation via CD28 and defective T cell stimulation.
Regulatory T Cells in the Immunodiagnosis and Outcome of Kidney Allograft Rejection
In the search of biomarkers for the diagnosis of cell mediated AR and prognosis of renal transplant, an increasing attention has been paid to the role of Tregs.
The analysis of some of the most important recent studies dealing with Tregs used as possible biomarker of acute kidney transplant rejection and/or prognostic factor related to the graft survival inspires some critical observations.
First of all it must be pointed out that most of the times the final assessment of the studies is affected by the modest statistical validity of the analyzed sample due to the small number of patients included.
On the other hand, it must be considered that renal biopsying for the diagnosing of allograft rejection is an invasive and time consuming procedure with some risk of complications and
not easily manageable for all patients.
Lastly, the different immunosuppressive therapies employed in the available studies and the potential effects on Treg expression and function constitute another critical variable to take into account in the evaluation of Treg function in the allograft outcome.
Treg are CD4 T cells with 2 subtypes according to from where they originate : n treg are natural that are originate in the thymus while peripheral treg originate from convertion native T cells peripherally, treg represent 5% of the total lymphocytes and more treg level means better graft outcome because they play important role in controlling immune response and effector T cells activity through IL-10 production ,treg characterized by express CD 25 and cytotoxic T lymphocytes Ag which will help to down regulate co stimulatory molecules on the dendritic cells of lymphoid organs and this will affect on T cell stimulation, there are markers that are used to detect treg activity like FOXP3 and IL-17 and by determining their percentage graft survival and rejection risk can be evaluated .
Treg cells plays an important role in graft tolerance. There are 2 types of Treg : thymus derived Treg and peripheral Treg ( it derived from naïve T cells in the periphery and is also called induced Treg)
Treg had many functions :
The use of Treg in the field of diagnosis has been studied by many studies :
Acute rejection is through different mechanisms one of which is by native T cells. they differentiate into cytotoxic or helper (TH1/TH2) or cytoprotective immunoregulatory T cells (Treg). Balance among these mechanisms is important.
Tregs:
play role in maintaining T cell homeostasis.
prevent activation of autoreactive immune response contributing to the maintenance of self-tolerance
by the production of IL-10 play role in the inhibition of t cell activity
can also induce perforin-dependent cytolysis of denatured cells in tumor-draining lymph nodes.
In a study of 90 patients, the high level of Treg cells was associated with higher graft survival at 4 and 5 years
Naïve T cells after activation differentiate into subsets of cytotoxic CD8+ and helper CD4+ T cells (TH1 and TH2) or into cytoprotective immunoregulatory T cells (Treg).
The immune reaction against a renal allograft has two main components: a destructive one mediated by CD4+ or CD8+ cytotoxic T cells and a protective response mediated by Tregs, and the balance between them identifies the fate of the graft and its survival.
Different roles of regulatory T cells in kidney transplantation:
Tregs and tolerance
Tregs originate mainly from the thymus (nTregs) or form from peripheral naïve T cell differentiation (iTregs).
Tregs prevent the activation of autoreactive immune responses and play a critical role in the maintenance of T cell homeostasis. Tregs express CD25 and CTLA-4 and release inhibitory cytokines including IL-10 and IL-35 that suggests a suppressor phenotype for these cells and a critical role in controlling the activation and function of T lymphocytes as well as of APC and NK cells.
Circulating Tregs present 5% of total lymphocytes in the blood. For the acquisition of full functional suppressive activity, Tregs need to be exposed to self-antigens or inflammation milieu. Inflammation plays an important role in the production of cytokines such as IL-10, TGF-beta, and Il-2, which are critical in the regulation of the immunosuppressive activity of Tregs.
Several mechanisms have been proposed to explain the role of Tregs in modulating immune response, such as:
IL-10 production that inhibits effector T cell activity.
The ability of CTLA-4 molecule to down regulate the expression of costimulatory molecules CD80 and CD86 on DCs, and as a result, inhibition of their activity.
Induction of perforin-dependent cytolysis of DCs
Therefore, Tregs can control DC activity by multiple mechanisms, and this results in the inhibition of effector T cell activation and promoting of functional tolerance.
Regulatory T Cells in the Immunodiagnosis and Outcome of Kidney Allograft Rejection
Identification of biomarkers to be able to discriminate between rejection and other causes of inflammation as well as correlating with outcome is a research challenge, and attention has been paid to the role of Tregs.
Induction of allograft tolerance by Tregs are not necessarily associated with reduction of response to the pathogens, so it is a promising approach in clinical transplantation.
FOXP3 transcripts, as a specific marker of Tregs, can be used as a prognostic marker of rejection reversal.
In one study, the higher level of FOXP3 transcripts in the urine sample of patients with acute rejection was observed. Indeed, transient expression of FOXP3 can be normal consequence of T cell activation without acquisition of the Treg phenotype. In addition, acute rejection with higher level of urinary FOXP3 correlated better with steroid responsiveness and better graft survival. In another study, correlation between FOXP3 and acute rejection showed the highest significance (94% sensitivity and 95% specificity).
A study reported that acute rejection was less common in the regulatory group of recipients (Foxp3+-infiltrating T lymphocytes in biopsies) than cytotoxic phenotype (dominated by Granzyme B+-T lymphocytes).
By an increasing the IL-17 to FOXP3 ratio, the allograft function significantly decreased in the acute cell mediated rejection setting.
In addition, patients with a higher levels of circulating Treg were associated with better long-term survival.
Tregs may play a role in antagonizing the inflammatory state associated with kidney transplantation. However, there are controversy in different studies about this vision.
Following exposure to antigens and activation of costimulatory molecules, peripheral naive CD4+ T cells can differentiate into different subpopulations : T helper 17 (Th17), Th1, Th2, and iTregs . Several transcription factors contribute to the functional specialization of these subsets, including Foxp3, ROR𝛾t, T-bet, and GATA3, which activate genes involved in the control of T cell function .
Tregs play a critical role in the maintenance of T cell homeostasis under different immune conditions. They prevent the activation of autoreactive immune responses, contribute to maintaining self-tolerance and homeostasis of the microbial flora of the gut, and promote the immunogenic escape of cancer cells .
In the search of biomarkers for the diagnosis of cell- mediated AR and prognosis of renal transplant, an increasing attention has been paid to the role of Tregs.
Inflammation plays an important role in driving the local cytokine milieu. In particular TGF-𝛽, IL-10, and IL-2 have been shown to be critical in regulating activation and/or maintenance of the immunosuppressive functions of Tregs
Tregs can control DC activity by multiple mechanisms, and this results in the inhibition of effector T cell activation and promoting of functional tolerance.
Foxp3/IL-17 ratio was a significant predictor for allograft outcome.
The level of circulating Tregs at peripheral blood level are associated with good long-term graft survival
In this case a combination of Foxp3 transcripts and creatinine levels proved to be a better prognosticator of rejection reversal than Foxp3 transcripts or serum creatinine levels alone.
Tregs may play a role in antagonizing the inflammatory state associated with kidney transplantation and may possibly be considered as a prognostic factor of outcome.
Different role of T reg in transplantation ; T reg is important component of the immune system and it represent the beneficial arm of rejection .They are about 5% of total lymphocytes and plays key tole in maintenance of T cells homeostasis and microbial flora of the gut homeostasis. Their role are summarised below ;
Regulatory T Cells in the Immunodiagnostic and Outcome of Kidney Allograft Rejection
Introduction:
Tregs represent 5% of total lymphocytes in blood. essential for maintaining peripheral tolerance:Tregs have cytoprotective and immune modulating effect Tregs play a critical role in the maintenance of T cell hemostasis under different immune conditions. their role in the immunodiagnostic of the acute rejection and the transplant outcome is diverse and need more understanding.
Aim of this study:
to identify the Treg cells effect in acute cellular rejection and assess their role as immunological biomarker that can predict the clinical transplant outcome.
Treg types:
1- (natural, nTregs) originated mainly from the thymus
2-(induced, iTregs) from CD4 subset activation and proliferation in secondary lymphoid tissue as part of costimulatory signal of Tcell activation.
Tregs effect on immune response.
Treg cells control the immune system in lymphoid and non-lymphoid tissues by many different mechanisms.
Inflammation triggers the expression of many local cytokines like TGF-𝛽, IL-10, and IL-2 which have very critical role in regulating activation and/or maintenance of the immunosuppressive functions of Treg cells soTreg cells can control the DCs activation by many mechanisms that lead to immune modulation and tolerance induction, for example the Treg cells expressing IL10 have direct and indirect inhibitory effectonthe T effector cells during infection , cancer and autoimmunity .while selective deletion of IL10 in Treg results in the development of spontaneous colitis, and activated immune responses at the skin level and lung interfaces.
Treg effect on immune function:
CTLA-4-expressing Tregs depends on the ability of CTLA-4 molecule to inhibit the expression of the CD80 / CD86 on dendritic cells (DCs) of lymphoid tissues resulting in impaired costimulation via CD28 and defective T- cell stimulation, Tregs can also induce perforin-dependent cytolysis of DCs in tumor-draining lymph nodes studies show stable contacts between Treg cells and APCs dendritic cells, confirming Treg cells mediated downregulation of these cells. and this results in the inhibition of effector T cell activation and enhance the functional immune tolerance and now on going clinical trails on using mAB to block some of the these costimaltory pathways .
Regulatory T Cells in the Immunodiagnosis and Outcome of Kidney Allograft Rejection
Nowadays there is increase interest about the role of Treg cells molecular markers for the diagnosis of T- cell mediated AR and as prognostic indicator of renal transplant outcome.
a direct and active involvement of Treg-mediated T cell suppression at the site of the tolerated transplants has been demonstrated, the specificity for donor antigens has not been fully evidenced.
In this review article, of total 8 studies with small numbers of patients range of 30-125 by using different Treg expressing markers including Foxp3 using real-time PCR from urinary cells or Treg FOXP3, m RNA, FOXP3 /1L17 expression cytolytic markers (perforin, granzyme B, and fas-ligand), peripheral blood mononuclear cell. All analyzed Treg -transcripts markers were higher in AR groups from different reported studies.
Muthu Kumar et al. in his study of 89 KT recipients assess the urinary FOXP3 as predictor for AR and found higher urinary Terg FOXP3 in the AR group (36 patients) as compared with the other two groups in addition patients who displayed both AR and higher urinary Foxp3 level showed better responsiveness to steroid treatment in 26 patients with significantly lower risk for graft failure as compared with subjects with lower levels of the transcription factor.
In another recent study from same author (Muthukumar et al), report that the urinary Foxp3 ,mRNA profiles and other molecules where able to associate with an early steroid withdrawal regimen with antithymocyte globulin induction, with excellent graft and patient outcomes in HIV-infected recipients of kidney allografts.
Another study by Mansour et al. [38] measured mRNA levels of Foxp3, Granzyme B, IFN-𝛾, IL-23, and ROR𝛾t in renal tissue of 46 untreated subjects with renal allografts with borderline rejection by Banff score Twenty-five patients were considered “nonprogressive,” as defined by serum creatinine
level below 110% of baseline during the 40 days following biopsy. While 21 patients were considered “progressive, as defined by an increase in serum creatinine level more than110% of baseline and by repeated histologic examinations showing AR,Ithe higher levels of Foxp3 mRNA were found in the nonprogressive group as compared with those observed in the progressive group.
Chung et al, assess the clinical significance of the ratio between IL-17-secreting cells and Treg infiltration in renal allograft tissues with acute T-cell-mediated rejection (ATCMR) in 56 patients and he confirm significant reduction in graft function in the groups with 1L17 higher ratio, with more sever IFTA, and lower 1-year and 5-year graft survival rates compared with patients with FOXP3 high ratio. with Multivariate analysis confirm that Foxp3/IL-17 ratio was a significant predictor for allograft outcome.
Tregs level at peripheral blood and the association with long-term graft survival were analyzed by flow cytometry in 90 kidney transplant recipients [41]. Patients who maintained high Treg levels (above 70%) at both 6 and 12 months shows a better long-term graft survival at 4- and 5-years follow-up.
Another study by Veronese et al. [35] he analyzes 73 graft biopsies and he reported that Tregs cells significantly higher in ACR type I and type II, with significant lower survival rate upon two years FU with higher Foxp3 score as compared with that observed in AHR and CNI toxicity; 96%Foxp3+ cells were CD4+ T lymphocytes aggregated within renal tubules.
CD4 positivity, and not Foxp3 mRNA expression, was independently associated with graft survival.as per Bunnag et al, study (36).
Concluding marks:
1-Small sample size in most of the reviewed studies can affect the final assessment and the validity of analyzed data.
2-Use the graft biopsy for diagnosis of rejection is rather invasive, and not without risk of complications
3-Moving toward a noninvasive molecular test could be more beneficial but still need more studies to confirm their validity
4-The use of a graft survival biomarker could be able to improve the prognostic validity of the procedure.
5-The effect of the different Immunosuppressive therapy used and its effect of the expression / function of Treg and CD 4 its very important variable to be reconsider in the evaluation of Treg function in the allograft outcome for example the rapamycin and steroid known to enhance and maintain the suppressive activity of Treg as compared to CNI effect. However, still difficult to differentiate the effects of different immunosuppressants,
One of the future goals is to use selective immunosuppressive agents that maintain and stabilize the suppressive activity of Treg
Tregs have a suppressive role, they control activation and function of T lymphocytes, APC and NK cells
Tregs are classified into natural Treg originating from thymus and induced TReg induced from stimulated peripheral conversion of naïve CD4+ T cells and are essential for maintaining peripheral tolerance.
Regulation of the immune response by Treg occur via several mechanisms:
produce IL-10 which inhibit effector T cell activity during infection, autoimmunity and cancer
CTLA-4 expressing Tregs regulate immune function as it decrease the expression of costimulatory molecules CD80 and CD86 on dendritic cells (DC) leading to impaired costimulation via CD28 and inhibited T cell stimuli.
Studies showed that Treg could control DC activity resulting in inhibited effector T cells activation and increased functional tolerance.
Regulatory T cells and the outcome of kidney allograft rejection
Direct role of Treg in T cell suppression was demonstrated at the site of tolerated transplant but the specificity for donor antigen wasn’t evidenced.
Allograft tolerance mediated by Treg don’t necessarily impair the response to invading pathogens encouraging the development of tolerance induction protocols in clinical transplant
A study showed that level of Foxp3 transcripts (used as specific marker of Treg) and creatinine level could be predictors of rejection reversal with considering the heterogenous nature of cellular components of rejection as Foxp3 could be derived from T cell activation without gaining regulatory function.
Another study analyzed biopsies having interstitial T lymphocyte infiltration between tubules and showed that patients with Foxp3 infiltrating T lymphocytes in biopsies didn’t develop acute rejection during 5 years of follow up
Also patients who had high level of Treg in peripheral blood at 6 and 12 months, had better graft survival at 4 and 5 years of follow up
However other studies showed that number of Tregs was significantly higher in acute cellular rejection, intragraft expression of Foxp3 mRNA wasn’t associated with better allograft outcome and and Foxp3 expression was higher in kidneys with cellular, humoral and mixed rejection than in kidneys without rejection.
Recent studies showed that immunosuppressive drugs have different effect on number and function of graft, corticosteroids and rapamycin improve the suppressive activity and survival of Treg while calcineurins inhibitor affect Treg function, However it is difficult to differentiate the effect of different immunosuppression.
T reg are suppressor CD4 T lymphocytes with high expression of both CD25 and transcription factor FoxP3. They are either natural T reg (thymus derived )or induced peripheral T regs (iT reg). T reg are essential for identifying self from non self Ags, inducing natural tolerance through controlling alloreactive T cells , tissue repair and restrict cancer initiation .
The role of T reg in kidney transplantation rejection was evalutated in several study as
1- Muthukumar et study who found significantly higher urinary levels of FOXP3 in patients with graft dysfunction and it was higher also in patients who responded better to immune suppression after acute graft rejection attack that may high light the role of FOXP3 as a diagnostic and prognostic marker for graft function .
2- The ration between IL17 producing cell and T reg cells ( represented by FOXP3 level ) in patients with acute T cell mediated rejection ,revealed more advanced histological changes specially tubulointerstitial injury and poorer graft function and outcome I group with higher IL17 producing T cell infilteration.
3- The peripheral T reg cell examined by flowmetry correlated with better short term graft outcome.
However , other studies reveled the reverse as Kaplan-Meier study showed poor graft outcome in patients with higher FOXP3 levels. While Bunnag et al. reveleaded more aggressive histological changes in high FOXP3 group compared to normal graft function group
These differences may be attributed to different immunesuppression protocols used in these studies with their variable effects on T reg number and functions, so further studies are necessary to establish the use of T reg as diagnostic and prognostic marker for graft function.
Treg are originate fromTcell .Their role is to suppress the immune destrcution of Tc ,APC and NK through IL10,IL35 .
Treg are two types
Natural {nTreg} from the thymus and induced {iTreg }converted from naive Tcell peripherally .
principal mechanisms of T-cell- mediated AR
Antigen will be express in APC so can be recognize by T cell This lead to activation and differentiation of Tcell in to TH1,TH2,TH17 AND i Treg,this induce cellular rejection .Their site of action is the endothelium through integrin LFA-1 and transmigration .Infiltration of T cell in to interstium lead to destruction .The damege can be mediated
1- directly through TNF and INF .
2-Indirectly Tc cell .
Treg are associated with abetter response to therapy and low risk of graft failure .
Investigation of Treg done through many techniques ,estimation of Foxp3 in urine or renal tissue and peripheral blood or mRNA of Foxp3 in urine cell or renal biopsy .Also ratio between Treg in renal tissue and IL-17.
Some study found that cellular rejection associated with high level of Treg leading to poor survival rate and graft outcome .
To over come this differance large pt must be enrolled with universal immunosuppressive protocol and use of non invasive markers rather than biopsy .
Treg are CD4 subpopulation expressing both CD25 molecule and CTLA-4 (cytotoxic T lymphocyte antigen) . Tregs originate mainly from the thymus (natural, nTregs) and from the peripheral conversion of naive CD4+ T cells under appropriate stimulus conditions (induced, iTregs). Circulating Tregs represent 5% of total lymphocytes in blood.
Treg regulate the immune response through production of IL-10,which is able to inhibit the effector T-cell activity . CTLA-4- expressing Tregs down regulate the expression of co stimulatory molecules CD80 and CD86 on dendritic cells (DCs) of lymphoid tissues resulting in impaired co stimulation via CD28 and defective T cell stimulation . Tregs can control DC activity by multiple mechanisms, and this results in the inhibition of effector T cell activation and promoting of functional tolerance.
Treg can be used as a biomarker of acute kidney transplant rejection and prognostic factor of graft survival . The use of a graft survival biomarker could be able to improve evaluation of response to immunosuppressive therapies.
Effects of immunosuppressive on Treg expression and function constitute another account in the evaluation of the allograft outcome. Corticosteroids and rapamycin have been shown to improve the suppressive activity and survival of Tregs.
.
Roles of Treg in Transplantation.
Tregs were identified as a CD4+ T cell subpopulation expressing CD25 [14] molecule and “cytotoxic T-lymphocyte antigen 4” (CTLA-4) at a similar extent to that displayed by activated T cells.The presence of CTLA- 4 and the release of inhibitory cytokines including IL-10 and IL-35 suggested a suppressor phenotype for these cells and critical role in controlling the activation and function of T lymphocytes as well as of APC and NK cells.
Origin of Treg : Tregs originate mainly from the thymus (natural, nTregs) and from the peripheral conversion of naive CD4+ T cells under appropriate stimulus conditions (induced, iTregs).
The immune reaction directed against a renal allograft has been suggested to be characterized by two major components: a destructive one mediated by CD4+ helper and CD8+ cytotoxic T cells and a protective response mediated by Tregs. The balance between these two opposite immune responses can significantly affect the graft survival.
Circulating Pool and Activation of Tregs: Circulating Tregs represent 5% of total lymphocytes in blood and they show a quiescent phenotype when isolated from a noninflammatory environment.
Tregs require functional activation for the acquisition of Treg full functional suppressive activity and that can be achieved following:
Inflammation plays an important role in driving the local cytokine milieu. In particular TGF–𝛽, IL-10, and IL-2 have been shown to be critical in regulating activation and/or maintenance of the immunosuppressive functions of Tregs.
The role of Tregs either:
(i) in the immunodiagnosis of transplant rejection. or
(ii) as predictor of the clinical outcome.
Treg and Tolerance
Tregs play a critical role in the maintenance of T cell homeostasis under different immune conditions.
1.Regulation of Immune Responses by Tregs:
2.Regulatory T Cells in the Immunodiagnosis and Outcome of Kidney Allograft Rejection
(i) One of the most important studies dealing with the role of Tregs in renal transplantation is the work of Muthukumar et al. :
(ii) In 2008, Aquino-Dias et al. analyzed the expression of perforin, granzyme B, and fas-ligand, together with Foxp3 using real-time PCR from urinary cells, peripheral blood mononuclear cells.
(iii) Mansour et al. measured mRNA levels of Foxp3, Granzyme B, IFN-𝛾, IL-23, and ROR𝛾t in renal tissue obtained from 46 untreated subjects with renal allografts with borderline lymphocytic infiltrates according to Banff scheme (changes insufficient for diagnosis of AR, including foci of tubulitis with mild to moderate cortical infiltration and without intimal arteritis):
(iv) In a retrospective study, Xu et al.:
(v) Chung et al. investigated the clinical significance of the ratio between IL-17- secreting cells and Treg infiltration in renal allograft tissues with acute T-cell-mediated rejection (ATCMR) on 56 patients with biopsy-proven ATCMR.
(vi)D.SanSegundo et al ; using flow cytometry in 90 kidney transplant recipients,analyzed the level of circulating Tregs at peripheral blood level and the association with long-term graft survival.
(vii) Veronese et al. analyzed 73 renal transplant biopsies selected for the diagnosis of acute cellular rejection (ACR) type I or type II, acute humoral rejection (AHR), or calcineurin inhibitor toxicity (CNI).
(viii) Bunnag et al. analyzed Foxp3 mRNA expression in 83 renal transplant biopsies for causes linked to histopathology.
(ix)Batsford et al. found no association between Foxp3 T cell expression and graft function one year after transplantation.
(x) Dummer et al. have recently observed that intragraft expression of both Foxp3 mRNA and protein was not associated with a better allograft outcome, analysed in terms of graft function and survival at 5 years after transplantation in 96 kidney transplants.
Tregs are CD4+CD25 high T lymphocytes expressing FoxP3 transcription factor either constitutively (thymic Tregs or tTregs) or after peripheral recognition of antigens (peripheral Tregs or pTregs).
1-role in self-antigen tolerance
2- suppress inflammatory alloreactive T cells in vitro and in vivo. They
3- inhibit alloreactivity in MLR in vitro and are thought to
4- mediate transplant tolerance elicited via leukocyte costimulation blockade, donor-specific transfusion.
CLINCAL IMPORTANCE OF Treg monitoring in clinical transplantation:
The importance of regulatory T-cells (Treg) in tolerance models makes their surface or intracellular markers obvious candidates to provide a biomarker for transplantation.Unfortunately, a definitive marker for Treg in humans is yet to be found.
Application of cell-based immunotherapy in organ transplantation to minimize the burden of immunosuppressive medication and promote allograft tolerance has expanded significantly over the past decade.
The classic Treg are enriched within the CD4+CD25+ T-cell population. To date, the most reliable marker available is forkhead box p3 (FOXP3), a member of the forkhead
winged helix family of transcription factors. In mice, Foxp3 is a specific marker of Treg , however in humans this transcription factor is also transiently expressed in nonregulatory T-cells upon activation. Other markers used to identify Treg include CD45RB CTLA-4, GITR, CD122, CD103, and galectin-10, and the absence of CD127 can also indicate a regulatory phenotype. A combination of these markers may be the best way of identifying Treg.
Foxp3+ CD4+ T cells are typically analyzed on bioptic samples.
Prognostic validity might be improved by using a graft survival biomarker, which could also be used to monitor immunosuppressive therapy responses.
To diagnose allograft rejection, renal biopsying is an invasive, time-consuming, and sometimes dangerous operation not suitable for everyone. To be sure, this strategy has to be tested on larger cohorts of transplanted patients taking into consideration all the factors discussed above.
For the assessment of Treg function in allograft outcome, it is important to consider the numerous immunosuppressive treatments used and their possible impact on Treg expression and function.
Some immunosuppressive medicines have been shown to increase the amount of Tregs while others reduce their activity.
T-reg function has been demonstrated to be affected by calcineurin inhibitors (CIs), although corticosteroids and rapamycin improved their suppressive efficacy and survival. In organ transplantation, however, it is difficult to distinguish between various immunosuppressants’ effects.
Thanks All
I just was stressing the importance of Treg in transplant immunology. I want to see more reflection on the paper.
I want to reassure you that we are moving towards clinical transplant immunology based on what we have studied in the past 5 weeks.
Regulatory T Cells in the Immunodiagnosis and Outcome of
Kidney Allograft Rejection
T reg are originally a subset of T cells which get activated upon encounter with the antigens. Their role is to suppress the immune destruction role of Tc, APC& NK through IL10 IL35.They have CD25 &CTLA-4. CTLA-4 down -regulate CD80&CD86 on dendretic cells preventing their encounter with CD28 .
There are two types :n Treg(natural) from the thymus and iTreg Tregs(induced;converted from naive t cells peripherally)
Principal Mechanisms of T-Cell-Mediated AR:
APC with the antigen will travel to lymphoid tissues where they underwent allorecognition by Tcells. This will result in T cells activation and differentiation into TH1.TH2,TH17 and iTreg. They will return to the graft to induce celluar rejection. Their main site of action is the endothelium of post capillary venules where tethering(through selectin to attach and increase the time of t cell encounter with the endothelium),adhesion to endothelium (through integrin LFA-1) and transmigration( infiltration of t cells into the interstium through gap junctions using diapedesis) .t cells will then destruct the interstisium through metalloproteases. The damage will destruct tubular epithelium and the endothelium and can be mediated :
1-indirectly through Tc cell(cytotoxic CD8+ T) and macropages .(Tc will destruct through perforin, granzyme B, granulolysins & Fas. Macrophages uses TNFα & NO)
2-directly through TNF & INF 𝛾 .
Many studies suggest that T reg are associated with a better response to therapy and lowe risk of graft failure . Treg were investigated through many techniques involving estimation of Foxp3 either in urinary cells , renal tissues and peripheral blood ,or mRNA profile of Foxp3in urine cells or renal tissue . ratio between IL-17- secreting cells and Treg infiltration in renal allograft tissues was also utilized.
On the other hand. Some studies contradict these findings . cases with cellular rejection were found to have higher level of Tregs ,survival rate and allograft outcome are less with higher Foxp3 scores , interstitial inflammation and tubulitis were associated with higher level of Foxp3 .
To overcome these variation in the future, large number of patients need to be enrolled, the need for biopsy samples should be replaced by non invasive markers and a universal protocol to avoid the effect of different immunosuppressive on Treg expression and function.
CMR process start when APC presented donor Ag to HLA I& II molecule, this will activate response against allograft causing activation of naive T cells which can differentiate into special subsets( destructive as CD4 & CD8, protective as Treg). So balance between protective & destructive T cells is very important for graft outcome.
Acute rejection can result from both cellular & Ab mediated immunity, & there are different types of cells participate in rejection as T cells, B cells, macrophages, plasma cells, eosinophils & neutrophils, but T cells are the central key in regulation of immune response. CD4 T cells can causing graft injury indirectly by activation of CD8 T cells & macrophages or/& directly through production of TNF & INF-gama.
Reg Cells are derived from CD4T cells ( with expression of CD25 & CTL4-A) , it secret inhibitory cytokines as IL-10 & IL-35 that have important role in controlling the function of T cells, NK & APC. T cells subsets have several transcription factors include Foxp2, RORyt, T bet & GATA3, these factors activate genes that can control T cell function. IL10 ( secreted by Treg) can inhibit the activity of effector T cells in infection, autoimmunity & cancer, while CTL4-A that expressed on Treg can inhibit expression co-stimulatory molecule CD80 & CD86 on DC leading to impaired CD28 & inhibit T cell function. In summary DC can be controlled by different mechanisms resulting in T cell inhibition & promoting of functional tolerance.
Several studies show that presence of Foxp3 & Foxp3 expression in transplanted kidney & urine in patients with acute rejection associated with good response to steroids & reversal of rejection & subsequent better graft survival. The result of other studies show no association between Foxp3 expression & better graft outcome.
Acute rejection is responsible for up to 12% of graft loss with the highest risk generally occurring during the first six months after transplantation. AR is classified into humoral and cellular rejections.
Recognition of donor allograft by recipient T lymphocyte results in activation of naive T cells that differentiate into subsets including cytotoxic CD8+ and helper CD4+ T cells type 1 (TH1) and TH2 cells or into regulatory T cells.
The immune reaction directed against a renal allograft has been suggested to be characterized by two major components: a destructive one mediated by CD4+ helper and CD8+ cytotoxic T cells and a protective response mediated by Tregs. Many studies have been performed in order to define the role of Tregs either in the immunodiagnosis of transplant rejection or as predictor of the clinical outcomeRegulatory T cells(Tregs) are a subset of CD4+ T cells. Tregs produced by a normal thymus are termed ‘natural’; nTreg. Treg formed by differentiation of naïve T cells outside the thymus, i.e. the periphery, or in cell culture are called ‘adaptive’ or inducible ; iTreg.
Natural Treg are characterised as expressing both the CD4 T cell co-receptor and CD25, which is a component of the IL-2 receptor. Treg are thus CD4+ CD25+. Expression of the nuclear transcription factor Forkhead box P3 (FoxP3) the determines natural Treg development and function. FoxP3 is essential for maintaining suppression of the immune system.
Regulatory suppressive mechanisms of T reg
Direct mechanisms by secreting cytokines such as IL-10, TGFβ and IL-35 and producing granzyme and perforin, leading to apoptosis or inhibition of effector cells
Indirect mechanisms b expression of CD39/CD73, which depletes the microenvironment of extracellular ATP via the generation of adenosine and AMP, molecules with implicated in immunosuppressive effects
They can sequester, by the high expression of CD25, IL-2, reducing effector T cells proliferation and differentiation
IL-2 starvation reduces NKs from proliferating and exhibiting effector functions
Some studies showed that higher urinary level of FoxP3 was associated with better response to corticosteroids, less rise in serum creatinine and better allograft outcome.
In a retrospective study evaluating protocol biopsies demonstrated that biopsy infiltrated with T reg (FoxP3+T lymphocytes) did not show any form of AR during 5 y period after biopsy while those infiltrated with cytotoxic T cells (Granzyme B+T lymphocytes) developed AR within 1 year after biopsy.
A study evaluating the correlation between ATCMR and the Tregs/Th17 ratio in the biopsy, found that graft rejection is associated with lower ratio.
Higher serum Treg is correlated with better graft survival. The level of peripheral circulating Treg was associated with better graft survival, patients with peripheral Treg of > 70% at 6, 12 m after transplantation are associated with better graft survival at 5 years.
Other studies demonstrated severity of kidney damage in the presence of Treg. Urinary FoxP3 was found to be higher in patients with acute rejection comparing to than patients without AR. In kidney biopsies for patients with acute rejection, higher number of Treg cells and FoxP3 was associated with more interstitial inflammation, tubulitis and lower graft survival
The immune reaction involved in the renal allograft is elicited by two major arms a destructive one mediated by CD4+ helper and CD8+ cytotoxic T cells and a defensive one mediated by Tregs.
Allograft rejection starts when the recipient’s T cells recognize the donor antigen on Antigen presenting cells , leads to T cell activation followed by differentiation.
Tregs was assed if possible to be used as possible biomarker of acute kidney transplant rejection and/or prognostic factor related to the graft survival
T reg induces tolerance by preventing the activation of autoreactive immune responses,
T reg represent a CD4+ T cell subpopulation expressing CD25 molecule and “cytotoxic T-lymphocyte antigen 4” (CTLA-4) suppressing the activation of T lymphocyte , APC ,NK cells .
Tregs produce IL-10, which inhibits, effector T cell activity during infection, autoimmunity, and cancer while CTLA-4 loss can cause severe lymphoproliferative disease and multiorgan autoimmunity.
Tregs can control Denderitic cell activity by multiplepathways , leading to inhibition of effector T cell and enhancing functional tolerance.
A study demonstrated that the levels of Foxp3 transcripts, as a specific marker of Tregs in cells obtained from urine samples of patients with AR were higher as compared with those in other groups analyzed; opposing expectations, this was justified by assuming that cells infiltrating the graft include both graft-destructive cells such as cytotoxic T cells and graft-protective Foxp3-expressing Tregs.
Another study concluded that combination of Foxp3 transcripts and creatinine levels together proved to be a better prognostic marker of rejection reversal then each one separately .
It was demonstrated that patients who displayed rejection and higher levels of urinary Foxp3 showed better response to steroid treatment with lower risk for graft failure in comparison to those with lower levels of Foxp3.
Multivariate analysis revealed that the Foxp3/IL-17 ratio was an important predictor for allograft outcome.
Authors published that high Treg levels at both 6 and 12 months revealed a better long-term graft survival at 4 and 5 years suggesting that Tregs can play a role in opposing the inflammatory state associated with kidney transplantation and can be considered as a prognostic marker.
Acute rejection is either humoral or cell mediated and It is responsible for 12% graft loss within the first 6 months.
Cellular rejection occurs when , APCs ptesents donor alloantigens through class I or class II HLA molecules, to naive T cells to initiate immune response, resulting in activation of naive T cells that differentiate into subsets including cytotoxic CD8+ and helper CD4+ T cells type 1 (TH1) and TH2 cells or into cytoprotective immunoregulatory T cells (Tregs).
several transactions factors contribute to the functional specification of this subsets including Foxp3, ROR𝛾t, T-bet, and GATA3, which activate genes involved on the control of T cell function.
immune reaction is either destructive mediated by CD4+ helper and CD8+ cytotoxic T cells or a protective mediated by T reg cells .
balanc between these two opposite responses affect the graft survival.
Treg and Tolerance
Regulatory T (Treg) cells are a subset of CD4+ T cells that is involved in maintaining immune homeostasis and self-tolerance by inhibiting the pro-inflammatory activities of CD4+ and CD8+ effector T cells, natural killer cells, and antigen-presenting cells.
It is either thymus derived( tTregs) or peripheral derived (pTregs) from the peripheral conversion of naïve CD4+ T cell
T reg cells Characterized by expression of CD4, CD25, FOXP3 (CD4+CD25+FoxP3+) and CTLA-4
Inflammatory cytokines like IL-10, TGF-β, and IL-2 have important role in maintenance of suppressive activity/function of Treg.
CTLA-4 cause defective co stimulation via CD28 through downregulation of expression of CD80 and CD86 on dendritic cells of lymphoid tissues
They can also induce perforin-dependent cytolysis of dendritic cells In tumor draining lymph nodes
loss of CTLA-4 in Ttreg cells lead to the development of severe lymphoproliferative and autoimmune disease.
Regulatory T Cells in the Immunodiagnosis and Outcome of Kidney Allograft Rejection
Number of studies have demonstrated the importance of T reg in inducing tolerance and improving graft survival
One of most important studies was based on the measurement of FOXP3 in urine sample of transplant patients and found that FOXP3 level was high in patients with acute rejection & a combination of FOXP3 transcripts and creatinine level proved to be better prognosticators of rejection reversal than FOXP3 or creatinine alone.
Patients who displayed acute rejection and high level of FOXP3 showed better response to steroids and lower risk of graft failure.
And another study showed that level of peripheral circulating Treg detected by FCM is correlated to graft survival, patients with peripheral Treg of > 70% at 6, 12 m after transplantation are associated with better graft survival at 5 years.
Although some studies didn’t show the same results and it was found that patients with acute rejection higher number of Treg cels and Foxp 3 score in biopsy are associated with more interstitial inflammation, tubulitis and lower graft survival.
The role of immunosuppressive drugs on number and function of Tregs is important as some studies showed that steroids and rapamycin improved its functions while CNI decreased its number and functions
Tregs represents 5% of total lymphocytes in the blood.
Tregs are essential for developing tolerance and this role has been demonstrated in tolerated skin allografts.
Many studies has been done to evaluate the role of Tregs in renal transplantation, one of the most important studies was based on the measurement of FOXP3 in urine sample of transplant patients and found that FOXP3 level was high in patients with acute rejection & a combination of FOXP3 transcripts and creatinine level proved to be better prognosticators of rejection reversal than FOXP3 or creatinine alone. Patients who displayed acute rejection and high level of FOXP3 showed better response to steroids and lower risk of graft failure.
Another study compared the level of FOXP3 to some molecules that are expressed by the cytolytic attack to the graft and found that FOXP3 level was higher in patients with rejection than those with acute tubular necrosis.
Another study found that urinary cell mRNA profiles for FOXP3 and other molecules were able to associate with an early steroid withdrawal regimen with ATG induction with excellent graft and patient outcomes in HIV infected recipients of kidney transplantation.
Another study to described the relation between FOXP3 level and disease progression in patients with boarderline rejection and found that higher level of FOXP3 found in non progressive disease.
Another study demonstrated the relation between the type of T cells infiltrating the graft( regulatory or cytotoxic) and the development of rejection and found that no patient with Tregs infiltration developed acute rejection during 5 years of follow up.
Multivariate analysis showed that the FOXP3/IL-17 ratio was a significant predictor of allograft outcome.
patients who maintained high level Tregs at 6&12 months displayed a better long term graft survival.
The number of Tregs was found to be significantly higher in acute TCM rejection type I&II as compared to ABMR and CNI toxicity however lower survival rate in patients with higher FOXP3.
kidneys with acute TCM rejection, ABMR and mixed rejection showed higher FOXP3 level as compared to kidneys without rejection.
higher expression of FOXP3 was associated with high level of inflammation and tubulitis.
Stimulation of T cell (naiive CD4) upon exposure to antigen, it will differentiate into many subsets different in function, T cell CD4 which express CD25 and CTLA-4 (cytotoxic T lymphocyte antigen 4 ) and has transcription factor Fox3p is called Treg (induced Treg iTreg).
There is also nTreg, which is natural Treg originate from thymus directly.
Treg is very important to maintain T cell homeostasis and control immune response, especially for self-antigens.
Treg represent 5% from circulating T lymphocytes and responsiple for peripheral tolerance , and it is recruited at mucosal surface when exposed to antigen there and also when exposed to self antigens.
Inflammatory cytokines like IL-10, TGF-β, and IL-2 have important role in maintenance of suppressive activity/function of Treg.
Treg produce IL-10 which inhibits T cell activation in cancer, autoimmune condition and infection.
Expression of CTLA-4 on Treg cells can impair co-stimulation pathway through CD28/CD86 on APCs, so impair T cell activation.
Treg can contact DC (dendritic cell) and induce its lysis and this will inhibit T cell activation and promote tolerance.
Graft biopsy is invasive procedure, and is operator dependent , so we should search for another marker or indicator to diagnose acute rejection as Treg or Fox3p level in the urine, but still need a lot of studies and research to reach the goal.
Immune response to allograft begins when donor antigens are carried out in complexes with HLA class I, II by APCS (immature dendritic cells) which then migrate to lymph node and spleen where they become mature, Mature APCS present antigen (either intact in case of donor APCS or processed in case of recipient APCS) to naïve T cells which differentiate into
1- CD4+ T helper which activate B cells, macrophages (delayed type hypersensitivity), CD8+ T cells, and produce inflammatory cytokines like TNF and IFN-𝛾 that cause direct injury to the graft.
2- CD8+ cytotoxic t cells with subsequent cell mediated cytotoxicity
3- T regulatory cells that suppress immune system
T regulatory (Treg) cells are a subclass of CD4 T cells that is responsible for suppression of immune response
It constitute 5% of CD4 positive T cell population
Characterized by expression of CD4, CD25, FOXP3 (CD4+CD25+FoxP3+)
It is either thymus derived( tTregs) or peripheral derived (pTregs) from the peripheral conversion of naïve CD4+ T cells
Transformation of naive CD4+ T cell to pTreg occur due to repeated stimulation to non- self antigen or exposure to certain cytokines (IL10, TGF-β)
Treg is important in initiating and maintaining peripheral tolerance as they suppress immune response by the following mechanisms :
A- Contact inhibition through surface expression of CTLA-4 medicated by Foxp 3
⦁ CTLA-4 cause defective co stimulation via CD28 through downregulation of expression of CD80 and CD86 on dendritic cells of lymphoid tissues
⦁ It was found that loss of CTLA-4 in Ttreg cells lead to the development of severe lymphoproliferative and autoimmune disease.
⦁ Tregs can also induce
B- Contact perforin-dependent cytolysis of dendritic cells
⦁ In tumor draining lymph nodes cytolysis of DCS occur under the effect of Treg
C- Non contact inhibition through the release of IL10 , TGF-β
⦁ It was found that selective deletion of IL10 in Tregs lead to the development of spontaneous colitis with marked skin and lung immune responses
The net result is :
⦁ Suppression CD4 T cell
⦁ Suppression of CD8+ T cells
⦁ May suppress B cells and dendritic cells
Several studies demonstrated beneficial effect of Treg cells in kidney allograft rejection
⦁ In patients with acute rejection the higher the urinary level of Foxp 3 the better is the response to corticosteroids, the less is the rise of serum creatinine and and the better is the outcome
⦁ In a retrospective study involving protocol biopsies which demonstrate no significant pathology based on Banff classification, biopsies were either infiltrated mainly by T reg (Foxp3+Tlymphocytes) or by cytotoxic T cells (Granzyme B+T lymphocytes). regulatory phenotype group did not show any form of AR during 5 y period after biopsy while cytotoxic phenotype group developed AR within 1 year after biopsy
⦁ A study addressing the relation between ATCMR and the Tregs/Th17 ratio in the biopsy of these patients found that graft rejection is associated with lower ratio
⦁ The level of peripheral circulating Treg detected by FCM is correlated to graft survival, patients with peripheral Treg of > 70% at 6, 12 m after transplantation are associated with better graft survival at 5 years
Other studies failed to demonstrated beneficial effect of Treg in kidney allograft rejection
⦁ In patients with acute rejection the level of urinary Foxp 3 was found to be higher than patients without AR
⦁ In patients with acute rejection the level of urinary Foxp 3 was found to be higher than patients without AR,
⦁ In patients with acute rejection higher number of Treg cels and Foxp 3 score in biopsy are associated with more interstitial inflammation, tubulitis and lower graft survival
An important part in this paper is this paragraph;
Recent clinical studies have demonstrated how different immunosuppressive drugs can influence differently the number and function of Tregs, by inducing stimulation, inhibition, or even noninterference. In particular, while corticosteroids and rapamycin have been shown to improve the suppressive activity and survival of Tregs, other treatments as calcineurin inhibitors (CIs) have been shown to affect Treg function
Thanks Rehab
Why it is important?
Dear Rehab
I’m still waiting for your reply
Role of Treg in transplant
1) play a role in the maintenance of T Cell homeostasis under different conditions, inhibit effector T cell activation and promoting functional tolerance to allogenic graft.
2)by preventing activation of auto reactive immune response contribute to maintaining self tolerance.
3)T regs produce IL-10 which inhibits directly or indirectly effector T cell activity during autoimmunity.
4) CTLA4 expressing Tregs downregulate the expression of costimulatory molecules CD80 and CD86 on APCs.
5) Tregs may play a role in antagonizing the inflammatory state associated with kidney transplantation and may possibly be considered as a prognostic factor of outcome.
6)Patients who maintained high Treg levels (above 70%) at both 6 and 12 months displayed a better long-term graft survival at 4 and 5 years followup.
7)corticosteroids and rapamycin improve the suppressive activity and survival of Tregs,calcineurin inhibitors (CIs) have affect Treg function.