Tolerance in Organ Transplantation

Transplantation is often the best option to treat organ end stage failure. Transplanted patients need to take long-term immunosuppressive drugs to inhibit rejection and maintain their graft. But those therapies have numerous important side effects such as cancer induction and opportunistic infections. Thus, the development of novel therapies to induce specific rather than general immunosuppression and therefore, tipping the balance between effector and regulatory functions to inhibit transplant rejection is a major goal in the field. One major approach is the blockade of costimulatory signals to abort effector T-cell activation following TCR engagement and to promote regulatory T cells. Here we summarized the research to date that details immune mechanisms involved in tolerance in organ transplantation and strategies toward tolerance

Anti-CD45RC antibody immunotherapy prevents and treats experimental autoimmune polyendocrinopathy-candidiasis- ectodermal dystrophy syndrome

Targeted monoclonal antibody (mAb) therapies show great promise for the treatment of transplant rejection and autoimmune diseases by inducing more specific immunomodulatory effects than broadly immunosuppressive drugs routinely used. We recently described the therapeutic advantage of targeting CD45RC, expressed at high levels by conventional T (Tconv) cells (CD45RC(hi)), their precursors, and terminally differentiated T (TEMRA) cells, but not by regulatory T cells (Tregs; CD45RC(lo/-)). We demonstrated efficacy of anti-CD45RC mAb treatment in transplantation, but its potential has not been examined in autoimmune diseases. Autoimmune polyendocrinopathy-candidiasis-ectodermal dystrophy (APECED) is a rare genetic syndrome caused by loss-of-function mutations of autoimmune regulator (AIRE), a key central tolerance mediator, leading to abnormal autoreactive T cell responses and autoantibody production. Herein, we show that, in a rat model of APECED syndrome, anti-CD45RC mAb was effective for both prevention and treatment of autoimmune manifestations and inhibited autoantibody development. Anti-CD45RC mAb intervention depleted CD45RC(hi) T cells, inhibited CD45RC(hi) B cells, and restored the Treg/Tconv cell ratio and the altered Treg transcriptomic profile. In APECED patients, CD45RC was significantly increased in peripheral blood T cells, and lesioned organs from APECED patients were infiltrated by CD45RC(hi) cells. Our observations highlight the potential role for CD45RC(hi) cells in the pathogenesis of experimental and human APECED syndrome and the potential of anti-CD45RC antibody treatment.Peer reviewe

Generation and analyse of a new model of APECED disease induced by Aire deficiency in rat

Les maladies auto-immunes sont dues à une rupture de la tolérance au soi et donc à un dysfonctionnement du système immunitaire. La protéine auto-immune regulator (Aire) est un régulateur de la transcription exprimé par les cellules épithéliales medullaires thymiques (mTEC) qui joue un rôle très important dans la tolérance centrale en régulant l’expression d’antigènes spécifiques de tissus (TSA) et ainsi la sélection négative des lymphocytes T immatures présentant un TCR de haute affinité pour un auto-antigène. Cependant, le rôle de Aire dans la sélection et la fonction des lymphocytes T régulateurs (Tregs) reste controversé. Nous avons généré un modèle de rats déficients pour Aire en utilisant la technologie des ZFN. En effet, nous avons pu mettre en évidence l’expression chez le rat, tout comme chez l’Homme, de Aire au niveau du messager mais aussi de la protéine dans le thymus et en périphérie. Nous avons décrit que ces rats présentent de forts symptômes auto-immuns comme l’alopécie, le vitiligo et l’ongulo-dystrophie, mais également des lésions histologiques importantes et de nombreux auto-anticorps circulant dans le sérum contre de nombreux organes. Nous avons également pu mettre en évidence un défaut de fonction des Tregs CD4+CD25hiCD127low in vivo dans un modèle de wasting disease mais pas de défaut des TregsCD8+CD45RClow.Autoimmune diseases are due to a break in selftolerance and to a dysfunction of the immune system. The autoimmune regulator protein (Aire) is a transcription regulator expressed by medullary thymic epithelial cells (mTEC). It is playing an important role in central tolerance by the negative selection of highly specific autoreactive T cells through the expression of tissue-specific antigens (TSA). However, the role of Aire in regulatory T cell selection remains unclear and controversial. We generated a model of Aire-deficient rat using the zinc finger nuclease (ZFN) technology. Indeed, we highlighted the same pattern of expression of Aire between rat and human in the thymus as well as in the periphery. We showed that Aire-deficient rats display strong auto-immune symptoms such as alopecia, vitiligo or nail dystrophy but also strong histological lesions and numerous circulating autoantibodies targeting numerous organs. We also evidenced a defect, in vivo, in a model of wasting disease, in the function of CD4+CD25hiCD127low Tregs but not CD8+CD45RClow

Rôle clé des Treg CD8 + spécifiques d’un allopeptide en transplantation

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Compensatory Regulatory Networks between CD8 T, B, and Myeloid Cells in Organ Transplantation Tolerance

International audienceIn transplantation tolerance, numerous regulatory populations have the capacity to inhibit allograft rejection; however, their compensatory capacities have never been clearly evidenced. We have previously demonstrated that the tolerogenic effect mediated by CD8+CD45RClow regulatory T cells (Tregs) in a model of organ transplantation with CD40Ig could be abrogated by permanent depletion of CD8+ cells that resulted in allograft rejection in half of the recipients. This result demonstrated that CD8+ Tregs were essential, but also that half of the recipients still survived indefinitely. We also demonstrated that no other regulatory populations, besides CD8+ Tregs, could induce and maintain allograft tolerance in CD40Ig-treated tolerant animals. In the current study, we analyzed the mechanisms that arose following CD8+ Treg depletion and allowed establishment of networks of new regulatory cells to maintain allograft survival. We identified regulatory B cells (Bregs) and regulatory myeloid cells (RegMCs) as being responsible of the maintenance of the long-term allograft survival. We demonstrated that both regulatory cell subsets efficiently inhibited antidonor immune responses in adoptively transferred recipients. Although Bregs were induced, they were not essential for the maintenance of the graft as demonstrated in IgM-deficient recipients. In addition, we showed that RegMCs were the most suppressive and acted alone, whereas Bregs activity was associated with increased suppressive activity of other subsets in adoptively transferred recipients. Altogether, to our knowledge, we demonstrated in this study for the first time the emergence of both Bregs and RegMCs following Tregs depletion and highlighted the importance of regulatory cell networks and their synergistic potential in transplantation

ANTI-CD45RC MABS IMMUNOTHERAPY CONTROLS THE DEVELOPPEMENT OF AUTO-IMMUNE SYMPTOMS IN AN APECED RAT MODEL OF AIRE DEFICIENCY

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Cross-Reactive Donor-Specific CD8+ Tregs Efficiently Prevent Transplant Rejection

International audienceTo reduce the use of non-specific immunosuppressive drugs detrimental to transplant patient health, therapies in development aim to achieve antigen-specific tolerance by promoting antigen-specific regulatory T cells (Tregs). However, identification of the natural antigens recognized by Tregs and the contribution of their dominance in transplantation has been challenging. We identify epitopes derived from distinct major histocompatibility complex (MHC) class II molecules, sharing a 7-amino acid consensus sequence positioned in a central mobile section in complex with MHC class I, recognized by cross-reactive CD8+ Tregs, enriched in the graft. Antigen-specific CD8+ Tregs can be induced in vivo with a 16-amino acid-long peptide to trigger transplant tolerance. Peptides derived from human HLA class II molecules, harboring the rat consensus sequence, also activate and expand human CD8+ Tregs, suggesting its potential in human transplantation. Altogether, this work should facilitate the development of therapies with peptide epitopes for transplantation and improve our understanding of CD8+ Treg recognition

IL-34 is a Treg-specific cytokine and mediates transplant tolerance

International audienceCytokines and metabolic pathway-controlling enzymes regulate immune responses and have potential as powerful tools to mediate immune tolerance. Blockade of the interaction between CD40 and CD40L induces long-term cardiac allograft survival in rats through a CD8+CD45RClo Treg potentiation. Here, we have shown that the cytokine IL-34, the immunoregulatory properties of which have not been previously studied in transplantation or T cell biology, is expressed by rodent CD8+CD45RClo Tregs and human FOXP3+CD45RCloCD8+ and CD4+ Tregs. IL-34 was involved in the suppressive function of both CD8+ and CD4+ Tregs and markedly inhibited alloreactive immune responses. Additionally, in a rat cardiac allograft model, IL-34 potently induced transplant tolerance that was associated with a total inhibition of alloantibody production. Treatment of rats with IL-34 promoted allograft tolerance that was mediated by induction of CD8+ and CD4+ Tregs. Moreover, these Tregs were capable of serial tolerance induction through modulation of macrophages that migrate early to the graft. Finally, we demonstrated that human macrophages cultured in the presence of IL-34 greatly expanded CD8+ and CD4+ FOXP3+ Tregs, with a superior suppressive potential of antidonor immune responses compared with non-IL-34-expanded Tregs. In conclusion, we reveal that IL-34 serves as a suppressive Treg-specific cytokine and as a tolerogenic cytokine that efficiently inhibits alloreactive immune responses and mediates transplant tolerance