Open access peer-reviewed chapter

Tolerance in Organ Transplantation

Written By

Laetitia Boucault, Séverine Bézie, Jason Ossart and Carole Guillonneau

Submitted: October 21st, 2015 Reviewed: February 22nd, 2016 Published: September 7th, 2016

DOI: 10.5772/62653

From the Edited Volume

Frontiers in Transplantology

Edited by Hesham Abdeldayem, Ahmed F. El-Kased and Ahmed El-Shaarawy

Chapter metrics overview

1,793 Chapter Downloads

View Full Metrics

Abstract

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.

Keywords

  • Transplantation
  • Tolerance
  • Costimulation
  • Tregs
  • Immunointervention

1. Introduction

The primary role of the immune system is to protect against foreign antigens without reacting against self-antigens. In this objective, some mechanisms of immune tolerance have been set up. Immune tolerance is defined in general by a total absence of specific reaction against antigens, and particularly self-antigens and a break in immune tolerance can lead to autoimmune disorders. Understanding the mechanisms of immunological tolerance is crucial for the development of strategies to manipulate the immune system in the context of organ transplantation. Here, we provide a comprehensive summary of the immune mechanisms involved in transplant rejection and tolerance induction and the research to date leading to new strategies toward tolerance, as well as their translation to the clinics.

Advertisement

2. Tolerance in organ transplantation

In the context of transplantation, the graft is recognized as foreign antigens and immune responses are triggered. Immunosuppressive treatments can repress total immune responses, including responses against the graft, but these drugs are well known for inducing side effects such as cardiovascular diseases or increased opportunistic infections and malignancies, and lead to high morbidity and mortality, even when avoiding excessive immunosuppression [1]. In addition, current immunosuppressive regimens have marginal effects on long-term allograft survival with for example a half-life of 10 years for kidney transplantation. In fact, these drugs can even be deleterious in the establishment of tolerance. Some cases of tolerance spontaneously acquired by patients who stopped their immunosuppressive treatments because of side effects and noncompliance have been reported [2, 3]. Tolerance in transplantation is defined by the following criteria: the graft must be definitely accepted without any lesions of chronic rejection, and the recipient should not be on treatment at the moment of analysis and should be able to develop immune responses against any other foreign antigen (i.e. immunocompetent), and thus represents the center of immunologist efforts working in the field of transplantation. The most commonly transplanted solid organ is the kidney, but the field of solid organ transplantation also includes the heart, liver, pancreas, lung or intestine. Nowadays, transplantation still remains the best solution for organ failure, even in the face of graft rejection. There are three types of solid graft rejection:

  1. The quickest mechanism of rejection, said hyperacute rejection, takes place between minutes to hours after transplantation. It is mediated by the presence of pre-existent circulating antibodies against A, B molecules expressed by red blood cells [4, 5] and acquired antibodies against the human leukocyte antigen (HLA) [6, 7]. Those antibodies allow the immune system of the grafted patients to strongly recognize the molecules present at the surface of graft endothelium and lead to the destruction of this endothelium through complement cascade, neutrophils, and monocytes. Nowadays, hyperacute rejection is no longer a concern due to the establishment of pre-transplantation tests as cross-match test, where closest HLA compatibility between donor and recipient is ensured (concerning mainly HLA-A, B, and DR) and blood group typing.

  2. The months following transplantation, acute rejection can occur. Two mechanisms can be involved in this process. The cell-mediated rejection is induced by presentation of alloreactive molecules by APCs (Antigen Presenting Cells) to recipient’s T lymphocytes, leading such activated lymphocytes to infiltrate and destroy the grafted organ [8]. The humoral mechanism acts through generation of alloantibodies directed mainly against MHC (major histocompatibility complex) class I by activated alloreactive B lymphocytes leading to antibody-dependent cellular cytotoxicity of endothelial cells (ADCC) [9]. Prevention of acute rejection is now ensured in more than 85% of cases by the current repertoire of immunosuppressive drugs available [10].

  3. Even though, the main problem in transplantation which remains unsolved is the long-term allograft dysfunction or chronic rejection. This phenomenon is slow and progressive but irreversible and cannot be controlled by immunosuppressive drugs. It is characterized by an increase of the thickness of the intima’s layer of graft vessels, leading to the ischemia of the tissue and finally to graft loss. Chronic rejection is mediated by the antigen-specific cellular and humoral immune responses against the graft. These immune responses lead to the recruitment of inflammatory mediators to the graft through the activation of the endothelium, and the secretion of free radicals and damage signals which activate muscle vessels proliferation.

Thus, T cells play an important role in graft rejection. In solid organ transplantation, naive T cells from the recipient are activated by recognition of blood group (ABO), donor major histocompatibility complex (MHC), minor histocompatibility complex (mHC, MICA, MICB, H-Y), or nonpolymorphic peptides (collagen, angiotensin II receptor) presented by professional APCs from the recipient or the donor or directly from endothelial cells of the graft (mostly MHC class I) [11]. Thus, T cells can be primed by three distinct pathways.

The direct allorecognition: when the transplanted organ is reperfused, intact MHC/peptide (MHCp) at the surface of APCs from the donor travel to the lymphoid organs of the recipients where they interact with CD4+ and CD8+ alloreactive naive T cells and active them [8, 12]. This pathway is generally associated with acute rejection because donor’s APCs persist a few months following transplantation. In addition, intact MHCp at the surface of endothelial cells of the graft can activate and maintain allogeneic CD8+ effector T-cell responses [13].

The indirect allorecognition: this pathway involves the presentation of allogeneic peptides derived from donor MHC molecules and presented by APCs of the recipient. Dominant peptides presented by this pathway are generally derived from hypervariable regions. This pathway involves capture, processing, and presentation of alloantigens and is predominantly used by CD4+ T cells and most of the alloantigens are presented by MHC class II. However, cross-presentation on MHC class I can occur and CD8+ T cells can also be activated [1416]. The indirect allopresentation pathway is also necessary for B cells activation, since their activation depends on CD4+ T cells help [17]. The indirect allorecognition is involved in both acute and chronic rejection since the alloantigens are present during all the life of the allograft [1821].

The semi-direct allorecognition: Lechler’s team reported that APCs from the recipient can capture entire intact MHC/peptide complexes expressed at the surface of the donor’s APCs. Those complexes are internalized, processed, and presented directly to CD8+ T cells or indirectly to CD4+ T cells. This presentation pathway involves the phenomenon of trogocytosis, i.e. the exchange of membrane fragments between cells in contact [2224]. Brown and al have reported in vivo, in a model of transplantation in mice, the presence of intact donor MHC-I and MHC-II on the surface of DCs, B cells, and macrophages [25].

2.1. The immune tolerance

To date, two elaborated and complementary mechanisms of immune tolerance have been described as central tolerance and peripheral tolerance (see Figure 1).

Figure 1.

Central and peripheral tolerance. In the thymus, tight interactions between TCRs and self-antigens presented by thymic epithelial cells (TEC) induce thymocytes apoptosis. Four mechanisms induce peripheral tolerance: ignorance, apoptosis, phenotypic skewing and anergy. Appropriate combination of signals results in complete T-cell activation.

2.1.1. Central tolerance

In the context of immune tolerance, the T lymphocyte lineage is particularly important. T lymphocytes, B lymphocytes, and NK cells derive from a common hematopoietic precursor from foetal liver during embryogenesis of from adult bone marrow. The CD3CD4CD8 TCR thymocytes colonize the thymus and undergo different stages of maturation leading to TCR rearrangement. During their migration to the cortex, cells also acquire expression of CD3, CD4, and CD8 molecules and undergo a step of positive selection. All CD4+CD8+cells said double-positive (DP) thymocytes express a complete αβTCR but only 20–25% of them are able to interact with the MHC [26, 27]. Cells that strongly interact with MHC class I become CD8+ simple positive (SP) and the one which interact with MHC class II becomes CD4+ SP [2830]. This interaction provides a survival signal to thymocytes that can pursue their education by migrating into the thymic medulla. In this medulla, SP thymocytes undergo the second step of immune central tolerance called negative selection. After positive selection, the TCR repertoire is very large and uncontrolled; thymocytes are able to recognize a broad range of foreign antigens but also self-antigens. The maturation of thymocytes expressing a TCR against self-antigens can lead to autoimmune disease in the periphery. Negative selection consists in the inhibition of potentially autoreactive thymocytes by clonal deletion or by induction of anergy if receptor editing fail. This selection is mediated by medullary thymic epithelial cells (mTECs) that are the only antigens presenting cells (APCs) expressing a panel of ectopic tissue-specific antigens (TSA). The expression of those TSA is mainly under control of a transcription regulator named Auto-Immune REgulator (AIRE) [31]. Two mechanisms of TSA presentations can occur in the medulla. The first one is the direct presentation by mTEC that can be sufficient to induce negative selection of both CD4+ and CD8+ T cells [32, 33]. The second mechanism of presentation is mediated by thymic dendritic cells which are able to get TSAs from mTECs and to present them to thymocytes [34]. Thymocytes able to strongly recognize a TSA presented by mTECs or DCs receive a signal that leads to apoptosis [35]. After negative selection, approximately 5% of total thymocytes can finally go to the periphery.

2.1.2. Peripheral tolerance

Due to the absence of self-antigen presentation in the thymus [36], or the low affinity of T cells for self-antigens [37], autoreactive T cells escape sometimes from thymic negative selection. To complete the efficacy of central tolerance, the immune system developed many tools to neutralize these cells and avoid autoimmune diseases. These mechanisms are either passive, concerning antigen ignorance, T-cell anergy or apoptosis induction and phenotypic skewing, or active when mediated by regulatory cells [38].

Antigen ignorance allows autoreactive T cells to persist as functional circulating T cells while never primed by any antigen [39]. Indeed, antigens can be masked by anatomical barriers like lens proteins, spermatozoids, or nervous system protein protected by the meninges barrier. Besides, a low amount of antigens can be sufficient to activate cytotoxic T lymphocytes previously primed but not naive T lymphocytes [40].

On the contrary, a high amount of antigen can induce T-cell apoptosis. This mechanism called activation-induced cell death is induced by Fas signaling pathway [41]. Indeed, Fas expression deficiency results in autoimmunity [42]. Autoreactive T-cell peripheral deletion can also result from a lack of costimulatory signal or of growth factor. [4345]. Likewise, the absence of costimulatory molecules induces a Fas-mediated apoptosis of autoreactive B cells [46], but anyway the autoreactive B cells escaping the clonal deletion are unlikely to meet the T cells specific to the same antigen they need to be completely primed [47, 48].

Autoreactive T cells can also be primed but functionally inactivated. This state of anergy is characterized by incapability to proliferate and to produce IL-2 following antigen stimulation [49, 50]. Antigens are required to maintain this inactive state [51], and large amounts of IL-2 or anti-OX40 antibodies can abrogate it [52]. Anergy results from either a lack of costimulatory signal by APCs, a low affinity of TCR for the antigen, or from CTLA4/B7 interaction. Indeed, interactions between CD28 expressed on T-cell surface and CD80-CD86 on antigen-presenting cells are essential for activation and proliferation of alloreactive T cells [53], allow generation of memory T cells and inhibit regulatory T (Tregs) suppressive activity [54, 55]. Without CD28/CD80-CD86 engagement, interactions between TCRs and alloantigens induce the anergy of T cells. CTLA-4 (CD152) has a large structural homology with CD28 and interacts with CD80-CD86 with better affinity than CD28 molecule and functions as a negative regulator of T-cell activation [56]. The expression of these two molecules regulates the balance between activation and inhibition of T cells and allows the control of an over-reaction of the immune system leading to inflammation or autoimmunity [57]. Similarly, the expression of Programmed Death-1 (PD-1) after antigenic stimulation and interaction with its ligand PDL-1 reduces IL-2 synthesis and induces T-cell anergy [58]. Another important co-stimulatory pathway is the CD40/CD40L co-stimulatory pathway. The CD40 molecule is a transmembrane protein that belongs to the TNF receptor family. It is expressed on vascular endothelial cells [59], activated DCs [60], monocytes/macrophages, platelets [61] and B lymphocytes [62]. The CD40L, also called CD154, exists in soluble form or at the cell membrane [63]. It is expressed on activated CD4+ T cells, basophiles, eosinophils [64], DCs from the blood [65], endothelial cells, macrophages [66], and B lymphocytes [67]. The CD40-CD40L interaction is critical for T-cell–dependent effector functions [68]. Indeed, CD40/CD40L interaction acts with IL-12 to induce production of IFN-y by human T lymphocytes stimulated by anti-CD3/anti-CD28, as well as IL-2 production by Th1 and IL-4, IL-5 and IL-10 by Th2 lymphocytes [69]. Besides, interaction with CD40 activates the expression of adhesion molecules by T lymphocytes [70]. Many other co-stimulation pathways are well described such as RANK/RANKL or ICOS/ICOSL. These costimulatory pathways are crucial for T-cell activation inducing rejection, so inhibition of one or more of these pathways may inhibit rejection. Moreover, anergized T cells can inhibit DCs function [71], become IL-10 producing Tregs [72], and induce T-cell apoptosis [73]. Autoreactive B cells also undergo anergy induced by chronic stimulation of BCR(B cell receptor) by antigens [74].

Activated autoreactive T cells can persist in a nonpathogenic state. Indeed, Th2 cytokines expression is linked to lower autoimmunity [75, 76] and tolerance in transplantation [7779], sometimes through Tregs induction [80]. By contrast, Th1 and Th17 are linked to allograft rejection [81]. Therefore, immunosuppressive treatments, like glucocorticoides or sirolimus, aim to inhibit Th1 responses and promote Th2 responses [82, 83].

Peripheral tolerance is also maintained by regulatory cells. Immune cells can acquire a regulatory function during development, such as “natural” Tregs in the thymus, or in periphery under the influence of the microenvironment, such as “induced” Tregs in the allograft or draining lymph nodes. Almost all type of cells have a regulatory counterpart, including T cells, B cells, myeloid cells (MDSCs, M2 macrophages), DCs. These regulatory cells limit effector cell responses to pathogens and self-antigens, acting by contact or by secretion of suppressive cytokines. In transplantation, regulatory cells are targets for therapeutic strategies to control innate immune responses triggered by ischemia/reperfusion of the graft, and adaptive responses triggered by the allograft.

Advertisement

3. Induction of tolerance

3.1. Animal models of tolerance

The immune system complexity is due to a large number of possible interactions and activation pathways. So, in vitroexperiments provide primary results but they need to be confirmed by in vivostudies to overview all the potential effects on the organism. There are lots of rodent models of allograft transplantation and numerous strategies have been used successfully to induce tolerance in these models.

Kidney transplantation is often used between MHC mismatched rodents [84, 85]. General physical condition is observed during all the experiments. Serum creatinine levels and urine quality are measured after transplantation to evaluate kidney activity. Generally, this graft is realized in different steps. First, ablation of one recipient kidney and allograft of MCH mismatched kidney. The transplanted organ is not immediately efficient. So, ablation of the second recipient’s kidney is realized few days after transplantation. At this time, the recipient has only one transplanted kidney. If the kidney is rejected, the rodent dies because of blood toxicity.

Cardiac allograft in rodent is also a good model [8690]. In this case, it is a heterotopic graft. Recipients keep its heart and receive a MHC-mismatched heart in the abdomen. The heart is connected to recipient blood circulation. Heart allograft survival is evaluated by palpation through the abdominal wall and scoring of its beating. Just after transplantation, heart beats strongly. But, if there is activation of the recipient immune system against alloantigens, the heart tissue is stiffened and beating are less intense and frequent until their full arrest. The major advantage of this model is that the recipient survives even if rejection occurred, and thus mechanisms can be analyzed.

But, sometimes, results obtained in rodent models could not be reproduced in larger animal models, such as non-human primates (NHPs) or swine. Rodents are too different from human to serve as preclinical models. Indeed, rodents have 90% similarity with human genome while there are around 99% similarity between NHP and human. Thus, NHPs constitute a more relevant animal transplant model. But, using NHPs is considerably more expansive and restrictive than rodents. Indeed, NHPs need more time for reproduction and development and more place than rodents. Moreover, all protocols conducted on animals have to be approved by an ethical comity. NHPs are ethically largely more controlled than rodents. So, first experiments are generally conducted on rodent models to generate primary results and conclusion. Then, a model with immune system more reflective of the human immune system is essential for testing protocols before moving into clinical studies.

This was the case for anti-CD40L treatment. All results obtained in rodents have demonstrated a great potential for induction of transplant tolerance. However, similar experiments in primate and human have highlighted a major barrier. Indeed, CD40L is a molecule expressed on NHPs, and human platelets. So this treatment resulted in thrombosis in NHPs and could not be used in the clinic [91, 92]. New anti-CD40L antibodies are being engineered as alternatives given the potential of this strategy in multiple diseases [9395].

An alternative possibility that has been developed in the last decade is the engineering of mouse with humanized immune system in which various types of human cells are engrafted and functional [96, 97]. These mice harbor a complete null mutation of the IL-2 receptor gamma chain, NOD/SCID IL-2r γnull (NSG), or Rag 2−/−γnull and are characterized by an impaired development and function of murine T, B and NK cells. These mice can efficiently support the development of a functional human hemato-lymphopoiesis. There are different protocols, more and more efficient, to induce humanization in highly deficient mice, such as injection of CD34+ cells or PBMCs. Mice humanized with PBMCs represent the fastest model of graft versus host disease (GVHD), due to direct injection of adult PBMCs. Indeed, these models allow the analysis of human immunology in vivo[98, 99]. The mice are monitored for weight loss and tissue damages.

Another important model is skin transplantation [100102]. It is possible to graft tailskin on the recipient lateral flank in rodent models. After removal of the bandage, grafts are observed to analyse their evolution. It’s considered as rejected when skin dries and falls, indeed no viable skin remains. This strategy is even more relevant in humanized mice model [103]. In this case, mice are grafted with human skin obtained from abdominal surgery from patients. In this kind of model, skins are left to engraft at least 15 days before rejection is triggered by injection of allogeneic PBMCs.

3.2. Co-stimulation blockade

The aim of transplantation research is to exploit mechanisms of self-tolerance to generate specific tolerance after transplantation. One of the most promising approaches is to inhibit co-stimulatory pathways to abort activation of T cells following TCR engagement. T cells are an essential component of the immune response against allogenic cells inducing allograft rejection. Interaction between TCR and MHC/antigen induces the first signal of stimulation. But this alloantigen recognition only is not sufficient for complete T cell activation. Co-stimulatory signals generated by the interaction between antigen and T cells and cytokine stimulation are also necessary for complete immune system activation [104]. There are 4 different co-stimulation molecules families: immunoglobulins superfamily, TNF receptors, integrin family, and T-cell immunoglobulin and mucin-containing domain (TIM) family.

Blockade of costimulatory pathways has been considered as a good strategy for the prevention of allograft rejection in transplantation by aborting activation following TCR engagement [52, 105]. These strategies have been studied in mice, rat, and NHPs and induces allograft tolerance [106, 107]. Blockade of both CD28/B7 and CD40/CD40L co-stimulatory pathways induces long-term allograft survival. In the ’90s, the first CTLA-4Ig soluble molecule was generated [108]. This molecule corresponds to the fusion between CTLA-4 extracellular domain and a modified IgG1 constant fragment domain [109]. CTLA-4Ig interaction with CD80-CD86 inhibits T-cell activation and prevents rejection of cardiac and renal allografts in rodent models [87, 108, 110] and prolongs survival of human islets xenograft in mice [111]. But CTLA-4Ig is not sufficient to induce tolerance because all allograft were finally rejected. Besides, when this treatment is combined with donor-specific transfusion (DST), allograft tolerance is obtained in heart allograft rodent models [105, 112]. DST corresponds to injection of donor splenocytes during transplantation and induces a state of chimerism. CD28 blockade show interesting results in rodent models, but this strategy is not efficient enough in NHP models [113]. Furthermore, it has been described that CTLA-4 is important for Tregs functions [114] and also for induction of tolerance to allograft [115, 116]. Thus, it would be more benefic to target CD28 molecule on T cell than CD80/CD86. Different groups have demonstrated that specific targeting of CD28 prevented rejection and generated Tregs [115, 117, 118]. FR104 has been developed in our laboratory as a costimulatory inhibitor that target CD28 without altering CD80/CD86 [119]. There are important differences between murine and human CD28 in terms of expression and interactions [120]. Thus, FR104 has been studied in NOD/SCID mice and NHP models. FR104 is safe in vitroand in vivoon human cells and does not play agonistic function on T cells [99]. This point is really important because another anti-CD28 molecule (TGN1412) studied in a phase 1 clinical trial induced important cytokine storm that caused life threatening effects [121].

CD40-CD40L blockade has also been studied for induction of transplantation tolerance. There are different strategies to block this pathway (monoclonal antibodies, CD40Ig). Treatment with monoclonal antibody anti-CD40L induces skin, renal, and cardiac allograft survival in mice [86, 122] and in NHP models [123, 124] but only with long-term repeated injections [123]. Some groups have shown that these monoclonal antibodies deplete activated T cells through cytotoxicity [125] and apoptosis [126], and induce Tregs [102]. These blockades of the CD40-CD40L pathway induce prolongation of allograft survival but without real allograft tolerance. Effect of anti-CD40L treatment has been improved by association with DST in islet graft in mice [127]. Different studies have demonstrated the importance of treatment associated with DST, such as anti-CD4, anti-thymocytes, or anti-CD40L [128130]. Another strategy uses CD40Ig molecule as treatment in allograft models. Our team has demonstrated that treatment with CD40Ig molecule or gene transfer induces allograft acceptance in cardiac allograft rat models [131] mediated by CD8+CD45RClow Tregs [132]. Several approaches use combined protocols. Indeed, anti-CD40L and CTLA-4Ig treatment synergies in heart and skin allograft in rodents [86, 101] and in renal allograft in NHPs [113].

ICOS-ICOSL pathway is another costimulatory pathway. ICOS presents around 40% similarity with CD28 and CTLA-4. ICOSL is constitutively expressed by B lymphocytes and monocytes and induced after T-cell activation [133]. Mice knocked out for ICOS have shown weak humoral responses [134136]. ICOS-ICOSL blockade alone does not really induce significant effect on graft outcomes [137]. Therefore, our team have demonstrated that blockade of both ICOS-ICOSL and CD40-CD40L induce long-term heart allograft survival in rat model and decreases chronic rejection lesions [138]. During acute rejection, RANK and RANKL molecules are increased. Moreover, RANKL blockade induce long-term heart allograft survival in both rats and mice [139], and blockade effect is stronger when associated with CD40 pathway. PD1 is expressed by activated T lymphocytes, B and NK cells and macrophages, while PDL1 and PDL2 are expressed by activated APCs. PD-L1Ig alone does not improve allograft survival but synergizes with cyclosporine A, rapamycin, and anti-CD40L [140]. This pathway seems to play a role in the generation of some Tregs [141, 142].

3.3. Regulatory cells, crucial players in tolerance

In the context of organ transplantation, the findings of the last decades have put lights on regulatory cells as key players in the induction and maintenance of tolerance in organ transplantation. Although it has become evident that several distinct subsets of regulatory cells have the capacity to finely and tightly regulate the anti-donor immune responses in organ transplantation, one subset has attracted most of the research, the CD4+CD25highCD127lowTregs, thanks to the identification of a crucial mastergene necessary for their development, identity, and function, the Foxp3 (Forkhead box P3) transcription factor [143146].

3.3.1. Regulatory T cells (Tregs)

Tregs suppression of immune responses has been unravelled in the ’70s [147]. Several subsets of Tregs have been evidenced including CD4+CD25highCD127low Tregs, but also CD8+ Tregs, among them the CD8+CD45RClow and CD8+CD28- Tregs are the most known, CD4CD8 Tregs, NKT cells and γδ T cells. Tregs can further be subdivided in characteristics (phenotype, repertoire…) and potential in organ transplantation depending of their emergence from the thymus (nTregs) or from the periphery (iTregs). While nTregs developed as a distinct lineage in the thymus, iTregs can be generated from naive cells in the periphery and can be in vitroor in vivoinduced in transplantation under some conditions such as donor-specific blood transfusion, blockade of the CD40/CD40L pathway, or donor MHC-derived peptides [148150].

Since the identification of the CD25 and Foxp3 markers, several other markers have been proposed to better define Tregs, such as for CD4+ Tregs glucocorticoid-induced tumor necrosis factor receptor family-related protein (GITR), CTLA-4, CD62L, CD103 (alpha beta integrin), LAG-3 and CD127 (alpha chain of the IL-7 receptor) [151155]. For CD8+ Tregs, the identification of relevant markers has been more difficult and several markers have been proposed such as CD122, CD28, CD45RC, CD103, and PD-1 [156160]. A major discovery for Tregs biology was the identification of the Foxp3 and its role in CD4+ Tregs development, identity and function [161, 162]. Mutations of the Foxp3 gene lead to a lymphoproliferative pathology in mice and an immune dysregulation polyendocrinopathy enteropathy X linked (IPEX) syndrome in human [163]. To date, this gene remains the best marker to identify CD4+ Tregs, although in human it has been demonstrated that it can be transitory upregulated in T lymphocytes upon activation without providing regulatory capacity [164]. The Helios and neuropilin-1 (Nrp-1) markers have also been proposed to distinguish nTregs from iTregs, and also more recently as an important marker for CD8+ Tregs identity and function [165167]. Indeed, the Cantor group demonstrated that Helios was a key transcription factor that stabilizes CD8+ Tregs in the context of an inflammatory response and that Helios-deficient Tregs developed an unstable phenotype (reduced Foxp3 and increased effector cytokines expression) during inflammatory responses. Antigen specificity has also been proposed to play an important role to distinguish Tregs origins [168]. Tregs originating from the thymus were selected for their specificity toward self-antigens, and thus are susceptible to be continuously stimulated by the self-antigens in periphery, potentially explaining their high expression of activation markers such as CD25, while iTregs generated by environmental conditions (inflammation, tolerance. . .) have a higher affinity toward exogenous antigens and thus are less stable once the antigens have been eliminated. In the context of organ transplantation, the antigens remain and we have demonstrated that CD8+CD45RClow iTregs were maintained and stable for a long time [132, 150].

Tregs use different mechanisms to suppress anti-donor immune responses; they can mediate their activity through cell contact, cytokines secretion, or metabolic disturbance. Suppression through cell contact is mediated by the CTLA-4 and LAG-3 molecules expressed by Tregs. Interaction of CTLA-4 with B7 modulates CD80-86 expression by APCs and tryptophan catabolism in DCs, thus inhibiting T-cell activation [169]. Tregs can also induce effector cells apoptosis by cytolysis mediated by cell contact and secretion of cytotoxic molecules such as granzyme B and perforin [170]. Suppression through metabolic disturbance consists in the modification of the biochemical and cytokine environment, leading to target cell death. Adenosine triphosphate (ATP), cyclic-adenosine-monophosphate (cAMP), or IL-2 deprivation has been shown has strong inhibitor of cell proliferation [171, 172]. Finally, immunosuppressive cytokines play a major role in Treg-mediated suppression. IL-10, TGF-β, IL-34, IL-35, FGL-2, and IFNγ are all involved in CD4+ and/or CD8+ Tregs function [89, 159, 173, 174]. We have demonstrated that IFNγ production by CD8+CD45RClow Tregs in a model of cardiac allograft tolerance in rat resulted in indoleamine 2,3-dioxygenase (IDO) expression by DCs and endothelial cells of the graft [159]. We have shown that CD8+CD45RClow iTregs also produced high levels of FGL-2 [89] and IL-34 in rat and we have demonstrated that IL-34 is a cytokine that is specifically expressed by human Foxp3+ CD4+ and CD8+ Tregs [173].

3.3.2. Other subsets of regulatory cells

Clinical and experimental observations have highlighted the role and potential of non–T cells with regulatory properties, defined as regulatory B cells (Bregs), tolerogenic dendritic cells (Tol-DCs), or regulatory macrophages (Mregs) or myeloid-derived suppressor cells (MDSCs) (nonexhaustive list) [89, 175179].

The role of Bregs has been particularly investigated in allograft models of tolerance by our laboratory and in tolerant transplanted patients. In these patients, high levels of B lymphocytes and B markers have been observed, while these patients were tolerant and displayed an absence of donor-specific antibodies (DSAs) [3, 180, 181]. The phenotypic profile of Bregs remains unclear, in contrast to Tregs, although a few markers have been identified including CD1d, CD21, CD24, and IgM and it has been demonstrated that they mostly display an immature phenotype [182, 183]. A common feature of Bregs is their ability to secrete IL-10 and IL-35, two cytokines playing a major role in their activity and initially demonstrated in autoimmune diseases [184]. Other mechanisms of action resulting in Bregs activation and suppression involve their BCR engagement, cooperation with T lymphocytes, signaling via CD40/CD40L, TLR activation, IFNγ from tolerogenic DCs, or granzyme B secretion [185189]. The engagement of their function results in inhibition of effector CD4+ T-cell proliferation, Th1 differentiation, APCs function, and monocytes activation. In addition, Bregs have been shown as able to induce Tregs and NKT cells [177, 190]. In the context of transplantation, the role of Bregs has been proven in a model of cardiac allograft tolerance in mice treated with anti-CD45RB [191]. In our laboratory, we have demonstrated that IgM+IgG B cells with a regulatory activity accumulated in the cardiac allograft of tolerant rat recipients and can adoptively transfer allograft tolerance to newly grafted recipients [183, 189]. We have shown that those Bregs had a partial defect in CD40 signaling and overexpressed granzyme B. In a similar model of cardiac allograft, we have demonstrated that administration of an adenovirus encoding fibroleukin-2 (FGL-2), a cytokine associated with Treg function, can induce tolerance to the allograft, thought generation of Bregs capable of infectious tolerance [89]. Finally, we have also demonstrated in a model of CD8+ Treg-mediated CD40Ig-induced allograft tolerance, depletion of CD8+ Tregs resulted in maintenance of long-term survival induction through generation of Bregs and RegMCs [176].

Although DCs are mostly known to be immunogenic; they also have the capacity to be tolerogenic. They play a major role in central and peripheral tolerance since they are involved in clonal deletion of autoreactive T lymphocytes in the thymus and correlate with an increased risk of autoimmune diseases and decreased presence of CD4+ Tregs when depleted in periphery [192]. They are defined by their expression of tolerogenic molecules, such as IL-10, indoleamine 2,3-dioxygenase (IDO), TGF-β or heme-oxygenase 1 (HO-1), their low expression of immunostimulatory molecules, such as MHC molecules or CD80 and CD86, and in general their ability to generate Tregs and to inhibit effector T-cell responses. Their tolerogenic properties have been linked with their maturation, exposure to immunosuppressive, or anti-inflammatory treatments and their environment [193]. In the last year, a number of protocols have been developed to generate Tol-DCs as therapeutic tools to induce a specific tolerance to antigens in autoimmune diseases and transplantation, and our laboratory is involved in the first clinical trial in kidney transplanted patients using Tol-DCs in the context of a European “ONE STUDY” funding involving several centers [194, 195].

Initially, the focus was on the potential of immature conventional DCs (cDCs) expressing low levels of MHC and costimulatory molecules and their potential to induce transplant tolerance to a cardiac graft in mice [196, 197]. Our laboratory has demonstrated that autologous DC combination with suboptimal dose of immunosuppressive drugs induces long-term allograft survival in rat [198]. We have shown that they require TMEM176B, an intracellular protein identified in tolerant recipients, to cross-present donor antigens and induce Tregs and prolong allograft survival [199]. We have also shown that the molecule HO-1 can inhibit DC maturation, while preserving their production of IL-10, and thus leading to inhibition of pro-inflammatory and allogeneic immune responses [200].

Although their tolerogenic properties in transplantation are less well defined, the role of plasmacytoid DCs (pDCs) has been demonstrated for the regulation and the maintenance of bone marrow and organ transplantation [201]. As for cDCs, they can be immunogenic or tolerogenic according to their receptor engagement and maturation status. We have demonstrated their preferential interaction with CD8+ Tregs in a model of cardiac allotransplantation in rat treated with CD40Ig resulting in the superior suppressive potential of CD8+CD45RClow Tregs [159, 202]. A group has shown their involvement in a model of cardiac allograft tolerance in mice treated with DST and anti-CD40L. In this model, pDCs induced tolerance through generation of alloantigen-specific CD4+CD25+Foxp3+ Tregs [203] and depletion of pDCs inhibited Treg development and tolerance induction. In human, pDCs stimulated through certain of their TLR (toll like receptor) or costimulatory molecules efficiently induced CD4+ and CD8+ Tregs inhibiting in vitroallogeneic T-cell stimulation [204206]. Liver-transplanted patients tolerating their allograft displayed significantly more pDCs and CD4+ Tregs [207].

Finally, Tregs can generate tolerogenic DCs, by modifying molecules expression such as inducing tolerogenic molecules expression like IDO, ILT3 or ILT4, changing their function [208]. We have demonstrated in several models of allograft tolerance that DCs were essential for establishment and maintenance of allograft tolerance [202, 209211].

In transplantation, although macrophages activation is often associated with allograft destruction and rejection in the early phases, the existence of an alternative population of Mregs contributing to tissue reparation, activated by Th2-type cytokine such as IL-4 and IL-13 and inhibiting pro-inflammatory cytokines secreted by macrophages [212]. Mregs can be induced by Treg interactions, Tregs depletions, and can even induce in turn Tregs via IL-10 secretion for example [213, 214]. The reduction of macrophages in mice receiving hematopoietic stem cells aggravated the GVHD, whereas expansion of macrophages with CSF-1 resulted in the opposite effect [215]. Mregs isolated from peripheral blood are characterized by their morphology, specific markers, although unstable, and their capacity to inhibit T-cell proliferation in vitro[216]. A clinical pilot study is administering donor-derived Mregs to kidney-transplanted patients, allowing graft survival under minimal immunosuppression one year following administration without clinical signs of graft rejection [217]. We and others have shown the potential of M-CSF and IL-34, two cytokines involved in monocytes survival and differentiation to induce Mregs in vitroand in vivoin human, mice, and rat transplantation models, and that those Mregs induced in turn Tregs capable of tolerance induction [173, 218].

MDSCs are a heterogeneous population of immature hematopoietic progenitor cells presenting numerous suppressive functions, including alloantigen tolerance induction in cardiac and islet allograft model in mice and kidney allograft in rat [219, 220].

3.4. Tipping the balance between effector and regulatory functions

Allograft outcome depends on the balance between effectors, which attack alloantigenic tissues, and regulators, which are essential for regulation/inhibition of alloresponses and induction of tolerance [221]. Induction of tolerance might be induced by the diminution of alloreactive T cells to allow Tregs to suppress the immune system activation. A large number of protocols have been studied with more or less efficacy.

Several approaches have been based on the expression amount of CD45 molecule on T cells allowing to distinguish effector and Tregs [222]. Strategies using monoclonal antibodies have been tested in animal models, notably in mice models of transplantation targeting CD45RB, as CD4+CD45RChigh T cells from untreated mice have been shown as capable of inducing colitis, diabetes, and thyroiditis [223]. In all cases where CD4+CD45RBhigh T cells have been shown to cause autoimmunity, their counterpart CD4+CD45RBlow T cells have been shown to prevent the induction of the disease. Anti-CD45RB antibody (MB23G2) caused transitory decrease of circulating lymphocytes expressing CD45RB and induced allograft survival with normal kidney allograft function [85]. This antibody induces also upregulation of CTLA-4 on lymphocytes [224]. This treatment has been studied in kidney, pancreatic islets, and heart allograft models. Lazarovits et al. have studied two different CD45RB mAb (MB23G2 and MB4B4). They have shown that the nondepleting MB4B4 is therapeutically ineffective while MB23G2 depletes CD45RBhigh lymphocytes and induces renal and islets allograft tolerance in mice model [85, 225].

Tipping the balance to favor regulatory functions is an interesting alternative to effector cells depletion. In our laboratory, we have developed and demonstrated the efficacy of different therapeutic strategies to modify the balance in favor of regulatory functions, such as CD40Ig, anti-CD28 (FR104), HO-1, FGL-2, or IL-34, for example [55, 89, 131, 173, 226]. Our team studied CD40Ig treatment in a cardiac allograft rat model. We have demonstrated that this treatment induces long-term survival by generation of CD8+CD45RClow[131]. CD45RC has been shown in rats, mice, and humans to be a marker of both CD4+ and CD8+ Tregs [98, 102106]. Moreover, this cell population is able to transfer infectious tolerance to naive transplanted rats[159]. Anti-CD28 is a good candidate to prevent rejection in the clinic [115, 231]. Zhang and al have shown that anti-CD28 inhibits lymphocytes activation and increases the proportion of cells expressing Foxp3 in the allograft. Our team and others have proved that treatment with anti-CD28 acts through the increase of the proportion of Tregs [117, 118, 178]. Actually, FR104 is the most known molecule targeting CD28. This humanized molecule has no agonist activity on human T cells in vitroand it does not induce cytokine storm in NOD/SCID mice reconstituted with human PBMCs. Moreover, Poirier and al have demonstrated the potential of FR104 in GVHD humanized mice model. They have also administrated FR104 to NHPs. Their results indicated a good tolerance in NHP and excluded cytokines release [99]. Several nondepleting antibodies, such as anti-CD4 and anti-CD8 mAb, are efficient to induce tolerance [232] and have permitted the first proof of the possibility of infectious tolerance [233]. Moreover, different strategies should be combined to improve their effects. Indeed, anti-CD45RB mAb and anti-CD40L mAb synergized and improved long-term allograft survival in islets and skin allografts [234].

All these examples confirm the importance of the balance between effector and regulatory cells for graft outcome.

Advertisement

4. From the bench to the clinic

Regulatory cells are essential for tolerance in transplantation. Many animal models have highlighted the potential of such tools for preventing allograft rejection and GVHD development. Their human counterparts are a promising issue for following immune status and inducing tolerance in transplanted patients.

4.1. New biomarkers for a real-time adapted treatment

A biomarker is “a characteristic that is objectively measured and evaluated as an indicator of normal biological processes, pathogenic processes, or pharmacologic responses to a therapeutic intervention” [235]. Nowadays, the reliability of the prognosis to predict allograft survival/rejection is low. For pancreas and liver transplantation, the measurement of lipase/amylase and liver enzymes respectively is recommended as routine post transplantation monitoring. The monitoring of cardiac enzymes is not recommended because of the poor sensitivity of these markers in the diagnosis of acute rejection, thus patients have to suffer endomyocardial biopsies 15 times during the first year after transplantation [236]. Echocardiography, diastolic function analysis, and quantitative measurement of changes of the transverse relaxation time T2 in the myocardium by magnetic resonance imaging are considered to improve cardiac allograft rejection prediction [237]. For renal allograft, the prognosis is generally based on creatinemia evolution and glomerular filtration. This prediction can be improved by calculating the kidney transplant failure score (KTFS) considering not only the creatinemia at 3 and 12 months post graft, but also the proteinuria at 12 months, the number of previous transplantations, the age and sex of the donor, the creatinemia of the donor at the harvesting time, and the incidence of an acute graft rejection in first year post transplantation [238].

Noncompliant patients spontaneously developing an operational tolerance to their graft are useful to identify new biomarkers and adapt in real time the care of patients. By comparing phenotypes of cells and cytokines from tolerant patients with healthy volunteers and patients rejecting their graft, we should be able to identify markers correlating with the immune status toward the graft. However, studies are limited to blood and urine analysis because of the ethical question of performing a biopsy of a tolerated graft. Kidney-grafted spontaneous operational tolerant patients are defined as having ceased all immunosuppressive drugs for more than one year, with no increase in serum creatinine during the last 12 months (CRT < 10%). Using microarray analysis, Brouard, Newell, and Sagoo compared genes differentially expressed in tolerant recipients with patients exhibiting chronic rejection [181, 239, 240]. Tolerant patients showed a reduction of activation markers of proinflammatory T cells, a down-regulation of pro-inflammatory cytokines [239], a GATA3 upregulation suggesting a Th2 deviation [241], and an increase in CD4+CD45RA-Foxp3hi memory Tregs versus patients with chronic rejection [3, 242, 243]. Interestingly, the three distinct studies and cohorts converge also with an increase of B cells in blood and CD20 transcript in urine in tolerant patients [180, 181, 240]. However, the phenotype of B cells named Bregs they described diverges [180, 181, 240, 244]. In liver-grafted spontaneous operational tolerant patients, higher numbers of CD4+CD25+CD127 T cells, Vδ1+ T cells, and NK cells were detected [245, 246].

The heterogeneity of treatments, in terms of dose and type of immunosuppressors administered to patients during chronic rejection episodes, and the heterogeneity of the parameters selected to monitor regulatory cells activity in the recent trials, prevents comparison of the results. To define general tolerance signatures, consortiums as The ONE Study and EU COST Action “BM1305: action to focus and accelerate cell-based tolerance-inducing therapies,” standardized immune monitoring of patients included in clinical trial [247]. Six panels of 7–9 markers designed are now standardized within 8 international laboratories to monitor T cells, B cells, and DCs [247].

Newly described cytokines associated with regulatory cells should be considered as prognostic markers. Recently, IL-34 has been closely associated with Tregs and M2 macrophages [173]. FGL2, produced by Tregs and generating Bregs, could also reflecting immune status of the graft [248]. Furthermore, nucleic acid analysis suggests new biomarkers for allograft rejection, such as donor-derived cell-free DNA (ddcfDNA) [249], OX40 [250], OX40L [250], PD-1 [250], Foxp3 [250] mRNA levels in urinary cells, and A20 [251], HO-1 [251], granzyme B [251], perforin [251], and Tim-3 mRNA [252] in both urinary cells and PBLs.

4.2. From patients observation to action

Many immunosuppressive drugs were developed these last decades. By targeting many cell types at different levels/pathways, their association largely contains the immune responses against the allograft. Briefly, glucocorticoids and calcineurin inhibitors (ciclosporin, tacrolimus) inhibit cytokine transcription in T lymphocytes and macrophages; mTOR inhibitors (rapamycin, everolimus [253]) inhibit expression of costimulatory molecules on APCs and T lymphocytes proliferation; cytostatics (cyclosphosphamide, methotrexate, azathioprine) and purines inhibitors (mycophenolate mofetil) inhibit T and B cell divisions; antibodies targeting thymocytes (ATG, thymoglobulin), CD3 or CD52 (Campath-1H) deplete T lymphocytes, CD25 (basiliximab, daclizumab) inhibit T lymphocytes activation, and CD20 (rituximab) and CD52 deplete B lymphocytes; sphingosine 1 phosphate inhibitor FTY720 (Fingolimod) retain lymphocytes in lymphoid organs and decrease their circulation in blood; efalizumab inhibits LFA-1 functions.However, drawbacks and side effects they induce are still unresolved.

The identification of new immunoregulatory mediators and the recent findings regarding regulatory cells over-represented in tolerant patients whereas lacking in graft-rejecting ones suggest new therapeutic strategies to control the immune balance. Several cytokines and antibodies have shown promising results in animal models. It has recently been shown that the cytokine IL-34 is able to induce Tregs through conversion of regulatory macrophages [173].Similarly, FGL2 can induce Bregs [248]. In addition, antibodies blocking costimulatory pathway like CD28 antagonist (FR104) or antibodies targeting TCR-associated signaling (CD45RC [254]) or DR3 [255] marker seem efficient to decrease T-cell function whereas promoting Tregs [55, 99, 256]. The promotion of regulatory cells is likely to induce lower drawback than classical broad-spectrum drugs.

Immunoregulatory cell therapy may be able to support peripheral tolerance and aims to induce a donor-specific unresponsiveness. This personalized method consists in harvesting blood cells from a patient, isolating and expanding ex vivoregulatory cells before re-infusing them to the patient in order to control allogeneic response against the graft in solid organ transplantation, or to control allogeneic response against the recipient infused with hematopoietic stem cells (HSCT) to avoid a GVHD reactions.

The first clinical trial was realized in 2009 by Trzonkowski et al, using 105 Tregs/kg expanded CD4+CD25+CD127 Tregs to reduce chronic GVHD symptoms [257]. In 2011, Brunstein began a phase I clinical trial and to date showed that until 3 × 106 expanded Tregs would be safe and efficient to reduce the incidence of grade II–IV aGVHD [258]. The same year, Di anni showed that freshly purified CD4+CD25+ Tregs counteracts the GVHD potential of a high number of donor Tcons in HLA-haploidentical HSCT [259]. In 2014, Martelli confirmed in a phase II clinical trial that co-infusion of freshly purified CD4+CD25+ Tregs significantly reduces GVHD incidence without affecting GVL (graft versus leukemia) effect [260]. In 2014, Bacchetta infused 105 donor T lymphocytes pretreated with IL-10/kg into recipient of HSCT and showed the protective effect of TR1 cells against GVHD [261]. Whereas these first clinical studies focused on Tregs in HSCT, several alternative regulatory cell types have been identified as potential sources for immunotherapies in solid organ transplantation. The EU-funded international ONE study consortium considers several immunoregulatory cell-based therapies for clinical management of solid organ transplant recipients and shares a common clinical protocol design. The ONE Study project titled “A Unified Approach to Evaluating Cellular Immunotherapy in Solid Organ Transplantation” aims to compare the feasibility and the potential of cell therapy by using MDSCs, Mregs, DC-10, Tol-DCs [262], rapa-DCs, monocytes conditioned with mesenchymal stem cells [263], Tr1 [264], and CD4+ Tregs [265]. CD8+ Tregs are now approaching clinical tests [266268] and Bregs are also considered as a tool for cell therapy [269].

Success of cell therapy to control allogeneic immune responses against the donor depends on regulatory properties of cells and on the number of regulatory cells infused into the recipient. Based on animal models and preclinical models of humanized mice, about 7 to 11 × 108 Tregs/kg would be necessary to control allogeneic response [270]. However, we have to consider the in vivoproliferation of Tregs after infusion [271]. Thus, the maximal infusible dose approved by The ONE Study for safety is 107 Tregs/kg [265]. Nowadays, Tregs from patients can be 100 to 1000 fold short-term expanded ex vivowhile keeping their suppressive properties [272274].

Importantly, clinical protocols also consider specificity of therapeutic cells against the graft donor. Indeed, antigen-specific Tregs have been shown more efficient in inhibiting anti-donor immune response [275]. The frequency of direct alloreactive Tregs has been estimated to 1–10% of total Tregs [276]. Injecting more donor-specific cells would amount to inject fewer cells, and to reduce nonspecific unwanted drawbacks. For Tang and Bluestone, the effect induced by 5 × 109 polyclonal CD4+ Tregs would be equivalent to the effect induced by 1.5 × 108 to 1 × 109 allogeneic Tregs [277]. That is why processes have been developed to expand Tregs specifically with APCs or antigen derived from the HLA donor. Indeed, CD4+ Tregs expanded with donor DCs or B cells, or by indirect presentation of donor cell lysate antigen onto recipient APCs [276], showed a higher suppressive activity compared to polyclonally expanded Tregs [275, 278280]. Similar protocols were used to generate donor-specific CD8+ Tregs [266]. Whereas TCR repertoire of donor APCs-expanded Tregs is still diverse, Tregs relatively efficiently reduce alloreactive T cell response without compromising general immunity according to mice models [266, 279]. Based on their capacity of infectious tolerance, Ag-specific Tregs can exert dominant tolerance to alloantigen in vivoby inducing regulatory properties in alloreactive T cells [281]. The identification of a unique shared peptide is of crucial interest today. Tregs with a unique antigen specificity can also be isolated and then expanded for cell therapy [282], or selected during the expansion by indirect presentation of one peptide [150, 267, 283]. Genetic engineering used to confer a TCR specificity to lymphocytes to redirect T cells in cancer immunotherapy [284, 285] offers new possibilities to obtain Tregs with an artificial specificity toward the graft donor Ag.

As cells will be re-infuse into the patient, all reagents used to culture cells have to be validated for “clinical grade,” and after expansion, cells are analyzed for purity and stability. Tregs are phenotypically characterized for expression of helios [167], DNA methylation status of the TSDR (Treg specific demethylated region) [286], while Foxp3 expression is no more sufficient [287], and tested in in vitrosuppression assay.

Cell therapy strategy would allow reducing the use of conventional immunosuppression in organ transplant recipients; nevertheless, clinical trials are rarely totally free of drugs for patients’ safety. This could affect regulatory cells survival and functions. Indeed, tacrolimus, mycophenolate mofetil (MMF), and methylprednisolone do not affect phenotype, function, or stability of Tregs, but reduce their proliferative capacity, whereas rapamycin did not [288290]. Moreover, rapamycin is sometimes used to maintain regulatory properties of Tregs during expansion culture and also to convert conventional CD4+ T cells into Tregs ex vivo[291]. By targeting upstream IL-2 synthesis, cyclosporine A compromises the homeostatic behaviour of CD4+ Tregs in peripheral immune compartments [292]. On the contrary, FTY720 synergizes with rapamycin for the conversion of CD4+ Tregs [293]. Thus, the choice of drugs combined with cell therapy has to be considered.

Advertisement

5. Conclusion

Research in transplantation has made considerable progresses improving transplantation outcomes, but important obstacles remain. Induction of tolerance is considered as the key to reduce the impact of toxic side effects of general immunosuppressive drugs. Better definition of immune tolerance mechanisms in human should lead to a better understanding of the potential effects of targeting strategies.

References

  1. 1. Marcén R. Immunosuppressive drugs in kidney transplantation: impact on patient survival, and incidence of cardiovascular disease, malignancy and infection. Drugs 2009;69(16):2227–43.
  2. 2. Ashton-Chess J, Giral M, Brouard S, Soulillou J-P. Spontaneous operational tolerance after immunosuppressive drug withdrawal in clinical renal allotransplantation. Transplantation 2007;84(10):1215–9.
  3. 3. Sagoo P, Perucha E, Sawitzki B, Tomiuk S, Stephens DA, Miqueu P, et al. Development of a cross-platform biomarker signature to detect renal transplant tolerance in humans. J Clin Invest. 2010;120(6):1848–61.
  4. 4. Porter KA. Morphological aspects of renal homograft rejection. Br Med Bull. 1965;21:171–5.
  5. 5. Kissmeyer-Nielsen F, Olsen S, Petersen VP, Fjeldborg O. Hyperacute rejection of kidney allografts, associated with pre-existing humoral antibodies against donor cells. Lancet 1966;2(7465):662–5.
  6. 6. Halloran PF, Wadgymar A, Ritchie S, Falk J, Solez K, Srinivasa NS. The significance of the anti-class I antibody response. I. Clinical and pathologic features of anti-class I-mediated rejection. Transplantation 1990;49(1):85–91.
  7. 7. Halloran PF, Schlaut J, Solez K, Srinivasa NS. The significance of the anti-class I response. II. Clinical and pathologic features of renal transplants with anti-class I-like antibody. Transplantation 1992;53(3):550–5.
  8. 8. Lechler RI, Batchelor JR. Restoration of immunogenicity to passenger cell-depleted kidney allografts by the addition of donor strain dendritic cells. J Exp Med. 1982;155(1):31–41.
  9. 9. Hippen BE, DeMattos A, Cook WJ, Kew CE, Gaston RS. Association of CD20+ infiltrates with poorer clinical outcomes in acute cellular rejection of renal allografts. Am J Transplant Off J Am Soc Transplant Am Soc Transpl Surg. 2005;5(9):2248–52.
  10. 10. Nankivell BJ, Kuypers DRJ. Diagnosis and prevention of chronic kidney allograft loss. Lancet Lond Engl. 2011;378(9800):1428–37.
  11. 11. Zhang Q, Reed EF. Non-MHC antigenic targets of the humoral immune response in transplantation. Curr Opin Immunol. 2010;22(5):682–8.
  12. 12. Larsen CP, Morris PJ, Austyn JM. Migration of dendritic leukocytes from cardiac allografts into host spleens. A novel pathway for initiation of rejection. J Exp Med. 1990;171(1):307–14.
  13. 13. Kreisel D, Krupnick AS, Balsara KR, Riha M, Gelman AE, Popma SH, et al. Mouse vascular endothelium activates CD8+ T lymphocytes in a B7-dependent fashion. J Immunol Baltim Md 1950. 2002;169(11):6154–61.
  14. 14. Celli S, Albert ML, Bousso P. Visualizing the innate and adaptive immune responses underlying allograft rejection by two-photon microscopy. Nat Med. 2011;17(6):744–9.
  15. 15. He C, Heeger PS. CD8 T cells can reject major histocompatibility complex class I-deficient skin allografts. Am J Transplant Off J Am Soc Transplant Am Soc Transpl Surg. 2004;4(5):698–704.
  16. 16. Joffre OP, Segura E, Savina A, Amigorena S. Cross-presentation by dendritic cells. Nat Rev Immunol. 2012;12(8):557–69.
  17. 17. Steele DJ, Laufer TM, Smiley ST, Ando Y, Grusby MJ, Glimcher LH, et al. Two levels of help for B cell alloantibody production. J Exp Med. 1996;183(2):699–703.
  18. 18. Auchincloss H, Lee R, Shea S, Markowitz JS, Grusby MJ, Glimcher LH. The role of “indirect” recognition in initiating rejection of skin grafts from major histocompatibility complex class II-deficient mice. Proc Natl Acad Sci U S A 1993;90(8):3373–7.
  19. 19. Morón G, Dadaglio G, Leclerc C. New tools for antigen delivery to the MHC class I pathway. Trends Immunol. 2004;25(2):92–7.
  20. 20. Fluck N, Witzke O, Morris PJ, Wood KJ. Indirect allorecognition is involved in both acute and chronic allograft rejection. Transplant Proc. 1999;31(1–2):842–3.
  21. 21. Dalchau R, Fangmann J, Fabre JW. Allorecognition of isolated, denatured chains of class I and class II major histocompatibility complex molecules. Evidence for an important role for indirect allorecognition in transplantation. Eur J Immunol. 1992;22(3):669–77.
  22. 22. Issa F, Schiopu A, Wood KJ. Role of T cells in graft rejection and transplantation tolerance. Expert Rev Clin Immunol. 2010;6(1):155–69.
  23. 23. Herrera OB, Golshayan D, Tibbott R, Salcido Ochoa F, James MJ, Marelli-Berg FM, et al. A novel pathway of alloantigen presentation by dendritic cells. J Immunol Baltim Md 1950. 2004;173(8):4828–37.
  24. 24. Jiang S, Herrera O, Lechler RI. New spectrum of allorecognition pathways: implications for graft rejection and transplantation tolerance. Curr Opin Immunol. 2004;16(5):550–7.
  25. 25. Brown K, Sacks SH, Wong W. Coexpression of donor peptide/recipient MHC complex and intact donor MHC: evidence for a link between the direct and indirect pathways. Am J Transplant Off J Am Soc Transplant Am Soc Transpl Surg. 2011;11(4):826–31.
  26. 26. Huesmann M, Scott B, Kisielow P, von Boehmer H. Kinetics and efficacy of positive selection in the thymus of normal and T cell receptor transgenic mice. Cell 1991;66(3):533–40.
  27. 27. Merkenschlager M, Graf D, Lovatt M, Bommhardt U, Zamoyska R, Fisher AG. How many thymocytes audition for selection? J Exp Med. 1997;186(7):1149–58.
  28. 28. Cosgrove D, Chan SH, Waltzinger C, Benoist C, Mathis D. The thymic compartment responsible for positive selection of CD4+ T cells. Int Immunol. 1992;4(6):707–10.
  29. 29. Laufer TM, DeKoning J, Markowitz JS, Lo D, Glimcher LH. Unopposed positive selection and autoreactivity in mice expressing class II MHC only on thymic cortex. Nature 1996;383(6595):81–5.
  30. 30. Capone M, Romagnoli P, Beermann F, MacDonald HR, van Meerwijk JP. Dissociation of thymic positive and negative selection in transgenic mice expressing major histocompatibility complex class I molecules exclusively on thymic cortical epithelial cells. Blood 2001;97(5):1336–42.
  31. 31. Anderson MS, Venanzi ES, Klein L, Chen Z, Berzins SP, Turley SJ, et al. Projection of an immunological self shadow within the thymus by the aire protein. Science 2002;298(5597):1395–401.
  32. 32. Gallegos AM, Bevan MJ. Central tolerance to tissue-specific antigens mediated by direct and indirect antigen presentation. J Exp Med. 2004;200(8):1039–49.
  33. 33. Hinterberger M, Aichinger M, Prazeres da Costa O, Voehringer D, Hoffmann R, Klein L. Autonomous role of medullary thymic epithelial cells in central CD4(+) T cell tolerance. Nat Immunol. 2010;11(6):512–9.
  34. 34. Koble C, Kyewski B. The thymic medulla: a unique microenvironment for intercellular self-antigen transfer. J Exp Med. 2009;206(7):1505–13.
  35. 35. Liu GY, Fairchild PJ, Smith RM, Prowle JR, Kioussis D, Wraith DC. Low avidity recognition of self-antigen by T cells permits escape from central tolerance. Immunity 1995;3(4):407–15.
  36. 36. Klein L, Klugmann M, Nave KA, Tuohy VK, Kyewski B. Shaping of the autoreactive T-cell repertoire by a splice variant of self protein expressed in thymic epithelial cells. Nat Med. 2000;6(1):56–61.
  37. 37. Bouneaud C, Kourilsky P, Bousso P. Impact of negative selection on the T cell repertoire reactive to a self-peptide: a large fraction of T cell clones escapes clonal deletion. Immunity 2000;13(6):829–40.
  38. 38. Walker LSK, Abbas AK. The enemy within: keeping self-reactive T cells at bay in the periphery. Nat Rev Immunol. 2002;2(1):11–9.
  39. 39. Ohashi PS, Oehen S, Buerki K, Pircher H, Ohashi CT, Odermatt B, et al. Ablation of “tolerance” and induction of diabetes by virus infection in viral antigen transgenic mice. Cell 1991;65(2):305–17.
  40. 40. Kurts C, Miller JF, Subramaniam RM, Carbone FR, Heath WR. Major histocompatibility complex class I-restricted cross-presentation is biased towards high dose antigens and those released during cellular destruction. J Exp Med. 1998;188(2):409–14.
  41. 41. Dhein J, Walczak H, Bäumler C, Debatin KM, Krammer PH. Autocrine T-cell suicide mediated by APO-1/(Fas/CD95). Nature 1995;373(6513):438–41.
  42. 42. Rieux-Laucat F, Le Deist F, Hivroz C, Roberts IA, Debatin KM, Fischer A, et al. Mutations in Fas associated with human lymphoproliferative syndrome and autoimmunity. Science 1995;268(5215):1347–9.
  43. 43. Ferber I, Schönrich G, Schenkel J, Mellor AL, Hämmerling GJ, Arnold B. Levels of peripheral T cell tolerance induced by different doses of tolerogen. Science 1994;263(5147):674–6.
  44. 44. Förster I, Hirose R, Arbeit JM, Clausen BE, Hanahan D. Limited capacity for tolerization of CD4+ T cells specific for a pancreatic beta cell neo-antigen. Immunity 1995;2(6):573–85.
  45. 45. Alexander-Miller MA, Leggatt GR, Sarin A, Berzofsky JA. Role of antigen, CD8, and cytotoxic T lymphocyte (CTL) avidity in high dose antigen induction of apoptosis of effector CTL. J Exp Med. 1996;184(2):485–92.
  46. 46. Rathmell JC, Townsend SE, Xu JC, Flavell RA, Goodnow CC. Expansion or elimination of B cells in vivo: dual roles for CD40- and Fas (CD95)-ligands modulated by the B cell antigen receptor. Cell 1996;87(2):319–29.
  47. 47. Russell DM, Dembić Z, Morahan G, Miller JF, Bürki K, Nemazee D. Peripheral deletion of self-reactive B cells. Nature 1991;354(6351):308–11.
  48. 48. Cyster JG, Hartley SB, Goodnow CC. Competition for follicular niches excludes self-reactive cells from the recirculating B-cell repertoire. Nature 1994;371(6496):389–95.
  49. 49. Jenkins MK, Schwartz RH. Antigen presentation by chemically modified splenocytes induces antigen-specific T cell unresponsiveness in vitro and in vivo. J Exp Med. 1987;165(2):302–19.
  50. 50. Schwartz RH. A cell culture model for T lymphocyte clonal anergy. Science 1990;248(4961):1349–56.
  51. 51. Schwartz RH. T cell anergy. Annu Rev Immunol. 2003;21:305–34.
  52. 52. Schwartz RH. T cell anergy. Annu Rev Immunol. 2003;21:305–34.
  53. 53. Greenfield EA, Nguyen KA, Kuchroo VK. CD28/B7 costimulation: a review. Crit Rev Immunol. 1998;18(5):389–418.
  54. 54. Zheng Y, Manzotti CN, Liu M, Burke F, Mead KI, Sansom DM. CD86 and CD80 differentially modulate the suppressive function of human regulatory T cells. J Immunol Baltim Md 1950. 2004;172(5):2778–84.
  55. 55. Poirier N, Azimzadeh AM, Zhang T, Dilek N, Mary C, Nguyen B, et al. Inducing CTLA-4-dependent immune regulation by selective CD28 blockade promotes regulatory T cells in organ transplantation. Sci Transl Med. 2010;2(17):17ra10.
  56. 56. Walunas TL, Lenschow DJ, Bakker CY, Linsley PS, Freeman GJ, Green JM, et al. CTLA-4 can function as a negative regulator of T cell activation. Immunity 1994;1(5):405–13.
  57. 57. Wood KJ, Goto R. Mechanisms of rejection: current perspectives. Transplantation 2012;93(1):1–10.
  58. 58. Chikuma S, Terawaki S, Hayashi T, Nabeshima R, Yoshida T, Shibayama S, et al. PD-1-mediated suppression of IL-2 production induces CD8+ T cell anergy in vivo. J Immunol Baltim Md 1950. 2009;182(11):6682–9.
  59. 59. Hollenbaugh D, Mischel-Petty N, Edwards CP, Simon JC, Denfeld RW, Kiener PA, et al. Expression of functional CD40 by vascular endothelial cells. J Exp Med. 1995;182(1):33–40.
  60. 60. McLellan AD, Sorg RV, Williams LA, Hart DN. Human dendritic cells activate T lymphocytes via a CD40: CD40 ligand-dependent pathway. Eur J Immunol. 1996;26(6):1204–10.
  61. 61. Inwald DP, McDowall A, Peters MJ, Callard RE, Klein NJ. CD40 is constitutively expressed on platelets and provides a novel mechanism for platelet activation. Circ Res. 2003;92(9):1041–8.
  62. 62. Kehry MR. CD40-mediated signaling in B cells. Balancing cell survival, growth, and death. J Immunol Baltim Md 1950. 1996;156(7):2345–8.
  63. 63. Ludewig B, Henn V, Schröder JM, Graf D, Kroczek RA. Induction, regulation, and function of soluble TRAP (CD40 ligand) during interaction of primary CD4+ CD45RA+ T cells with dendritic cells. Eur J Immunol. 1996;26(12):3137–43.
  64. 64. Gauchat JF, Henchoz S, Fattah D, Mazzei G, Aubry JP, Jomotte T, et al. CD40 ligand is functionally expressed on human eosinophils. Eur J Immunol. 1995;25(3):863–5.
  65. 65. Pinchuk LM, Klaus SJ, Magaletti DM, Pinchuk GV, Norsen JP, Clark EA. Functional CD40 ligand expressed by human blood dendritic cells is up-regulated by CD40 ligation. J Immunol Baltim Md 1950. 1996;157(10):4363–70.
  66. 66. Mach F, Schönbeck U, Sukhova GK, Bourcier T, Bonnefoy JY, Pober JS, et al. Functional CD40 ligand is expressed on human vascular endothelial cells, smooth muscle cells, and macrophages: implications for CD40-CD40 ligand signaling in atherosclerosis. Proc Natl Acad Sci U S A. 1997;94(5):1931–6.
  67. 67. Grammer AC, Bergman MC, Miura Y, Fujita K, Davis LS, Lipsky PE. The CD40 ligand expressed by human B cells costimulates B cell responses. J Immunol Baltim Md 1950. 1995;154(10):4996–5010.
  68. 68. Grewal IS, Flavell RA. The role of CD40 ligand in costimulation and T-cell activation. Immunol Rev. 1996;153:85–106.
  69. 69. Peng X, Kasran A, Warmerdam PA, de Boer M, Ceuppens JL. Accessory signaling by CD40 for T cell activation: induction of Th1 and Th2 cytokines and synergy with interleukin-12 for interferon-gamma production. Eur J Immunol. 1996;26(7):1621–7.
  70. 70. Barrett TB, Shu G, Clark EA. CD40 signaling activates CD11a/CD18 (LFA-1)-mediated adhesion in B cells. J Immunol Baltim Md 1950. 1991;146(6):1722–9.
  71. 71. Vendetti S, Chai JG, Dyson J, Simpson E, Lombardi G, Lechler R. Anergic T cells inhibit the antigen-presenting function of dendritic cells. J Immunol Baltim Md 1950. 2000;165(3):1175–81.
  72. 72. Buer J, Lanoue A, Franzke A, Garcia C, von Boehmer H, Sarukhan A. Interleukin 10 secretion and impaired effector function of major histocompatibility complex class II-restricted T cells anergized in vivo. J Exp Med. 1998;187(2):177–83.
  73. 73. Chai JG, Bartok I, Scott D, Dyson J, Lechler R. T:T antigen presentation by activated murine CD8+ T cells induces anergy and apoptosis. J Immunol Baltim Md 1950. 1998;160(8):3655–65.
  74. 74. Gauld SB, Benschop RJ, Merrell KT, Cambier JC. Maintenance of B cell anergy requires constant antigen receptor occupancy and signaling. Nat Immunol. 2005;6(11):1160–7.
  75. 75. Bradley LM, Asensio VC, Schioetz LK, Harbertson J, Krahl T, Patstone G, et al. Islet-specific Th1, but not Th2, cells secrete multiple chemokines and promote rapid induction of autoimmune diabetes. J Immunol Baltim Md 1950. 1999;162(5):2511–20.
  76. 76. Young DA, Lowe LD, Booth SS, Whitters MJ, Nicholson L, Kuchroo VK, et al. IL-4, IL-10, IL-13, and TGF-beta from an altered peptide ligand-specific Th2 cell clone down-regulate adoptive transfer of experimental autoimmune encephalomyelitis. J Immunol Baltim Md 1950. 2000;164(7):3563–72.
  77. 77. Karczewski J, Karczewski M, Glyda M, Wiktorowicz K. Role of TH1/TH2 cytokines in kidney allograft rejection. Transplant Proc. 2008;40(10):3390–2.
  78. 78. Yin H, Li X-Y, Jin X-B, Zhang B-B, Gong Q, Yang H, et al. IL-33 prolongs murine cardiac allograft survival through induction of TH2-type immune deviation. Transplantation 2010;89(10):1189–97.
  79. 79. Amarnath S, Chen H, Foley JE, Costanzo CM, Sennesh JD, Solomon MA, et al. Host-based Th2 cell therapy for prolongation of cardiac allograft viability. PLoS One 2011;6(4):e18885.
  80. 80. Zhang D, Sanchez-Fueyo A, Kawamoto K, Alexopoulos SP, Zhang W, Zheng XX. Th1 to Th2 immune deviation facilitates, but does not cause, islet allograft tolerance in mice. Cytokine 2010;51(3):311–9.
  81. 81. Xie A, Wang S, Zhang K, Wang G, Ye P, Li J, et al. Treatment with interleukin-12/23p40 antibody attenuates acute cardiac allograft rejection. Transplantation 2011;91(1):27–34.
  82. 82. Franchimont D. Overview of the actions of glucocorticoids on the immune response: a good model to characterize new pathways of immunosuppression for new treatment strategies. Ann N Y Acad Sci. 2004;1024:124–37.
  83. 83. Libetta C, Sepe V, Zucchi M, Portalupi V, Meloni F, Rampino T, et al. The effect of sirolimus- or cyclosporine-based immunosuppression effects on T-cell subsets in vivo. Kidney Int. 2007;72(1):114–20.
  84. 84. Sayegh MH, Akalin E, Hancock WW, Russell ME, Carpenter CB, Linsley PS, et al. CD28-B7 blockade after alloantigenic challenge in vivo inhibits Th1 cytokines but spares Th2. J Exp Med. 1995;181(5):1869–74.
  85. 85. Lazarovits AI, Poppema S, Zhang Z, Khandaker M, Le Feuvre CE, Singhal SK, et al. Prevention and reversal of renal allograft rejection by antibody against CD45RB. Nature 1996;380(6576):717–20.
  86. 86. Hancock WW, Sayegh MH, Zheng XG, Peach R, Linsley PS, Turka LA. Costimulatory function and expression of CD40 ligand, CD80, and CD86 in vascularized murine cardiac allograft rejection. Proc Natl Acad Sci U S A. 1996;93(24):13967–72.
  87. 87. Baliga P, Chavin KD, Qin L, Woodward J, Lin J, Linsley PS, et al. CTLA4Ig prolongs allograft survival while suppressing cell-mediated immunity. Transplantation 1994;58(10):1082–90.
  88. 88. Chen L, Wang T, Zhou P, Ma L, Yin D, Shen J, et al. TLR engagement prevents transplantation tolerance. Am J Transplant Off J Am Soc Transplant Am Soc Transpl Surg. 2006;6(10):2282–91.
  89. 89. Bézie S, Picarda E, Tesson L, Renaudin K, Durand J, Ménoret S, et al. Fibrinogen-like protein 2/fibroleukin induces long-term allograft survival in a rat model through regulatory B cells. PloS One 2015;10(3):e0119686.
  90. 90. Lin H, Bolling SF, Linsley PS, Wei RQ, Gordon D, Thompson CB, et al. Long-term acceptance of major histocompatibility complex mismatched cardiac allografts induced by CTLA4Ig plus donor-specific transfusion. J Exp Med. 1993;178(5):1801–6.
  91. 91. Kawai T, Andrews D, Colvin RB, Sachs DH, Cosimi AB. Thromboembolic complications after treatment with monoclonal antibody against CD40 ligand. Nat Med. 2000;6(2):114.
  92. 92. Boumpas DT, Furie R, Manzi S, Illei GG, Wallace DJ, Balow JE, et al. A short course of BG9588 (anti-CD40 ligand antibody) improves serologic activity and decreases hematuria in patients with proliferative lupus glomerulonephritis. Arthritis Rheum. 2003;48(3):719–27.
  93. 93. Shock A, Burkly L, Wakefield I, Peters C, Garber E, Ferrant J, et al. CDP7657, an anti-CD40L antibody lacking an Fc domain, inhibits CD40L-dependent immune responses without thrombotic complications: an in vivo study. Arthritis Res Ther. 2015;17:234.
  94. 94. Tocoian A, Buchan P, Kirby H, Soranson J, Zamacona M, Walley R, et al. First-in-human trial of the safety, pharmacokinetics and immunogenicity of a PEGylated anti-CD40L antibody fragment (CDP7657) in healthy individuals and patients with systemic lupus erythematosus. Lupus 2015;24(10):1045–56.
  95. 95. Xie JH, Yamniuk AP, Borowski V, Kuhn R, Susulic V, Rex-Rabe S, et al. Engineering of a novel anti-CD40L domain antibody for treatment of autoimmune diseases. J Immunol Baltim Md 1950. 2014;192(9):4083–92.
  96. 96. Shultz LD, Ishikawa F, Greiner DL. Humanized mice in translational biomedical research. Nat Rev Immunol. 2007;7(2):118–30.
  97. 97. Legrand N, Cupedo T, van Lent AU, Ebeli MJ, Weijer K, Hanke T, et al. Transient accumulation of human mature thymocytes and regulatory T cells with CD28 superagonist in “human immune system” Rag2(-/-)gammac(-/-) mice. Blood 2006;108(1):238–45.
  98. 98. Ji M, Jin X, Phillips P, Yi S. A humanized mouse model to study human immune response in xenotransplantation. Hepatobiliary Pancreat Dis Int HBPD INT. 2012;11(5):494–8.
  99. 99. Poirier N, Mary C, Dilek N, Hervouet J, Minault D, Blancho G, et al. Preclinical efficacy and immunological safety of FR104, an antagonist anti-CD28 monovalent Fab’ antibody. Am J Transplant Off J Am Soc Transplant Am Soc Transpl Surg. 2012;12(10):2630–40.
  100. 100. Kingsley CI, Karim M, Bushell AR, Wood KJ. CD25+CD4+ regulatory T cells prevent graft rejection: CTLA-4- and IL-10-dependent immunoregulation of alloresponses. J Immunol Baltim Md 1950. 2002;168(3):1080–6.
  101. 101. Larsen CP, Elwood ET, Alexander DZ, Ritchie SC, Hendrix R, Tucker-Burden C, et al. Long-term acceptance of skin and cardiac allografts after blocking CD40 and CD28 pathways. Nature 1996;381(6581):434–8.
  102. 102. Honey K, Cobbold SP, Waldmann H. CD40 ligand blockade induces CD4+ T cell tolerance and linked suppression. J Immunol Baltim Md 1950. 1999;163(9):4805–10.
  103. 103. Feng G, Nadig SN, Bäckdahl L, Beck S, Francis RS, Schiopu A, et al. Functional regulatory T cells produced by inhibiting cyclic nucleotide phosphodiesterase type 3 prevent allograft rejection. Sci Transl Med. 2011;3(83):83ra40.
  104. 104. Lafferty KJ, Woolnough J. The origin and mechanism of the allograft reaction. Immunol Rev. 1977;35:231–62.
  105. 105. Turka LA, Linsley PS, Lin H, Brady W, Leiden JM, Wei RQ, et al. T-cell activation by the CD28 ligand B7 is required for cardiac allograft rejection in vivo. Proc Natl Acad Sci U S A. 1992;89(22):11102–5.
  106. 106. Ford ML, Larsen CP. Translating costimulation blockade to the clinic: lessons learned from three pathways. Immunol Rev. 2009;229(1):294–306.
  107. 107. Li XC, Strom TB, Turka LA, Wells AD. T cell death and transplantation tolerance. Immunity 2001;14(4):407–16.
  108. 108. Linsley PS, Brady W, Urnes M, Grosmaire LS, Damle NK, Ledbetter JA. CTLA-4 is a second receptor for the B cell activation antigen B7. J Exp Med. 1991;174(3):561–9.
  109. 109. Lenschow DJ, Walunas TL, Bluestone JA. CD28/B7 system of T cell costimulation. Annu Rev Immunol. 1996;14:233–58.
  110. 110. Azuma H, Chandraker A, Nadeau K, Hancock WW, Carpenter CB, Tilney NL, et al. Blockade of T-cell costimulation prevents development of experimental chronic renal allograft rejection. Proc Natl Acad Sci U S A 1996;93(22):12439–44.
  111. 111. Lenschow DJ, Zeng Y, Thistlethwaite JR, Montag A, Brady W, Gibson MG, et al. Long-term survival of xenogeneic pancreatic islet grafts induced by CTLA4lg. Science 1992;257(5071):789–92.
  112. 112. Sayegh MH, Zheng XG, Magee C, Hancock WW, Turka LA. Donor antigen is necessary for the prevention of chronic rejection in CTLA4Ig-treated murine cardiac allograft recipients. Transplantation 1997;64(12):1646–50.
  113. 113. Kirk AD, Harlan DM, Armstrong NN, Davis TA, Dong Y, Gray GS, et al. CTLA4-Ig and anti-CD40 ligand prevent renal allograft rejection in primates. Proc Natl Acad Sci U S A 1997;94(16):8789–94.
  114. 114. Wing K, Onishi Y, Prieto-Martin P, Yamaguchi T, Miyara M, Fehervari Z, et al. CTLA-4 control over Foxp3+ regulatory T cell function. Science 2008;322(5899):271–5.
  115. 115. Zhang T, Fresnay S, Welty E, Sangrampurkar N, Rybak E, Zhou H, et al. Selective CD28 blockade attenuates acute and chronic rejection of murine cardiac allografts in a CTLA-4-dependent manner. Am J Transplant Off J Am Soc Transplant Am Soc Transpl Surg. 2011;11(8):1599–609.
  116. 116. Markees TG, Phillips NE, Gordon EJ, Noelle RJ, Shultz LD, Mordes JP, et al. Long-term survival of skin allografts induced by donor splenocytes and anti-CD154 antibody in thymectomized mice requires CD4(+) T cells, interferon-gamma, and CTLA4. J Clin Invest. 1998;101(11):2446–55.
  117. 117. Guillonneau C, Séveno C, Dugast A-S, Li X-L, Renaudin K, Haspot F, et al. Anti-CD28 antibodies modify regulatory mechanisms and reinforce tolerance in CD40Ig-treated heart allograft recipients. J Immunol Baltim Md 1950. 2007;179(12):8164–71.
  118. 118. Haspot F, Séveno C, Dugast A-S, Coulon F, Renaudin K, Usal C, et al. Anti-CD28 antibody-induced kidney allograft tolerance related to tryptophan degradation and TCR class II B7 regulatory cells. Am J Transplant Off J Am Soc Transplant Am Soc Transpl Surg. 2005;5(10):2339–48.
  119. 119. Mary C, Coulon F, Poirier N, Dilek N, Martinet B, Blancho G, et al. Antagonist properties of monoclonal antibodies targeting human CD28. mAbs 2013;5(1):47–55.
  120. 120. Yao S, Zhu Y, Zhu G, Augustine M, Zheng L, Goode DJ, et al. B7-H2 Is a Costimulatory ligand for CD28 in human. Immunity 2011;34(5):729–40.
  121. 121. Suntharalingam G, Perry MR, Ward S, Brett SJ, Castello-Cortes A, Brunner MD, et al. Cytokine storm in a phase 1 trial of the anti-CD28 monoclonal antibody TGN1412. N Engl J Med. 2006;355(10):1018–28.
  122. 122. Markees TG, Phillips NE, Noelle RJ, Shultz LD, Mordes JP, Greiner DL, et al. Prolonged survival of mouse skin allografts in recipients treated with donor splenocytes and antibody to CD40 ligand. Transplantation 1997;64(2):329–35.
  123. 123. Kirk AD, Burkly LC, Batty DS, Baumgartner RE, Berning JD, Buchanan K, et al. Treatment with humanized monoclonal antibody against CD154 prevents acute renal allograft rejection in nonhuman primates. Nat Med. 1999;5(6):686–93.
  124. 124. Elster EA, Xu H, Tadaki DK, Montgomery S, Burkly LC, Berning JD, et al. Treatment with the humanized CD154-specific monoclonal antibody, hu5C8, prevents acute rejection of primary skin allografts in nonhuman primates. Transplantation 2001;72(9):1473–8.
  125. 125. Monk NJ, Hargreaves REG, Marsh JE, Farrar CA, Sacks SH, Millrain M, et al. Fc-dependent depletion of activated T cells occurs through CD40L-specific antibody rather than costimulation blockade. Nat Med. 2003;9(10):1275–80.
  126. 126. Blair PJ, Riley JL, Harlan DM, Abe R, Tadaki DK, Hoffmann SC, et al. Cd40 ligand (Cd154) triggers a short-term Cd4+ T cell activation response that results in secretion of immunomodulatory cytokines and apoptosis. J Exp Med. 2000;191(4):651–60.
  127. 127. Parker DC, Greiner DL, Phillips NE, Appel MC, Steele AW, Durie FH, et al. Survival of mouse pancreatic islet allografts in recipients treated with allogeneic small lymphocytes and antibody to CD40 ligand. Proc Natl Acad Sci U S A 1995;92(21):9560–4.
  128. 128. Omoto K, Nishimura Y, Nomoto K, Kong YY, Umesue M, Murakami Y, et al. Anti-CD4 monoclonal antibody reduces the dose of cyclophosphamide required to induce tolerance to H-2 haplotype identical skin allografts in mice. Immunobiology 1996;195(1):16–32.
  129. 129. Mayumi H, Good RA. The necessity of both allogeneic antigens and stem cells for cyclophosphamide-induced skin allograft tolerance in mice. Immunobiology 1989;178(4-5):287–304.
  130. 130. Seung E, Mordes JP, Rossini AA, Greiner DL. Hematopoietic chimerism and central tolerance created by peripheral-tolerance induction without myeloablative conditioning. J Clin Invest. 2003;112(5):795–808.
  131. 131. Guillot C, Guillonneau C, Mathieu P, Gerdes CA, Ménoret S, Braudeau C, et al. Prolonged blockade of CD40-CD40 ligand interactions by gene transfer of CD40Ig results in long-term heart allograft survival and donor-specific hyporesponsiveness, but does not prevent chronic rejection. J Immunol Baltim Md 1950. 2002;168(4):1600–9.
  132. 132. Guillonneau C, Hill M, Hubert F-X, Chiffoleau E, Hervé C, Li X-L, et al. CD40Ig treatment results in allograft acceptance mediated by CD8CD45RC T cells, IFN-gamma, and indoleamine 2,3-dioxygenase. J Clin Invest. 2007;117(4):1096–106.
  133. 133. Yoshinaga SK, Whoriskey JS, Khare SD, Sarmiento U, Guo J, Horan T, et al. T-cell co-stimulation through B7RP-1 and ICOS. Nature 1999;402(6763):827–32.
  134. 134. Dong C, Juedes AE, Temann UA, Shresta S, Allison JP, Ruddle NH, et al. ICOS co-stimulatory receptor is essential for T-cell activation and function. Nature 2001;409(6816):97–101.
  135. 135. Dong C, Temann UA, Flavell RA. Cutting edge: critical role of inducible costimulator in germinal center reactions. J Immunol Baltim Md 1950. 2001;166(6):3659–62.
  136. 136. Tafuri A, Shahinian A, Bladt F, Yoshinaga SK, Jordana M, Wakeham A, et al. ICOS is essential for effective T-helper-cell responses. Nature 2001;409(6816):105–9.
  137. 137. Salama AD, Yuan X, Nayer A, Chandraker A, Inobe M, Uede T, et al. Interaction between ICOS-B7RP1 and B7-CD28 costimulatory pathways in alloimmune responses in vivo. Am J Transplant Off J Am Soc Transplant Am Soc Transpl Surg. 2003;3(4):390–5.
  138. 138. Guillonneau C, Aubry V, Renaudin K, Séveno C, Usal C, Tezuka K, et al. Inhibition of chronic rejection and development of tolerogenic T cells after ICOS-ICOSL and CD40-CD40L co-stimulation blockade. Transplantation 2005;80(4):546–54.
  139. 139. Guillonneau C, Louvet C, Renaudin K, Heslan J-M, Heslan M, Tesson L, et al. The role of TNF-related activation-induced cytokine–receptor activating NF-κB interaction in acute allograft rejection and CD40L-independent chronic allograft rejection. J Immunol. 2004;172(3):1619–29.
  140. 140. Ozkaynak E, Wang L, Goodearl A, McDonald K, Qin S, O’Keefe T, et al. Programmed death-1 targeting can promote allograft survival. J Immunol Baltim Md 1950. 2002;169(11):6546–53.
  141. 141. Aramaki O, Shirasugi N, Takayama T, Shimazu M, Kitajima M, Ikeda Y, et al. Programmed death-1-programmed death-L1 interaction is essential for induction of regulatory cells by intratracheal delivery of alloantigen. Transplantation 2004;77(1):6–12.
  142. 142. Wang L, Pino-Lagos K, de Vries VC, Guleria I, Sayegh MH, Noelle RJ. Programmed death 1 ligand signaling regulates the generation of adaptive Foxp3+CD4+ regulatory T cells. Proc Natl Acad Sci U S A 2008;105(27):9331–6.
  143. 143. Sakaguchi S, Sakaguchi N, Asano M, Itoh M, Toda M. Immunologic self-tolerance maintained by activated T cells expressing IL-2 receptor alpha-chains (CD25). Breakdown of a single mechanism of self-tolerance causes various autoimmune diseases. J Immunol Baltim Md 1950. 1995;155(3):1151–64.
  144. 144. Shevach EM. The resurrection of T cell-mediated suppression. J Immunol Baltim Md 1950. 2011;186(7):3805–7.
  145. 145. Fontenot JD, Rasmussen JP, Williams LM, Dooley JL, Farr AG, Rudensky AY. Regulatory T cell lineage specification by the forkhead transcription factor foxp3. Immunity 2005;22(3):329–41.
  146. 146. Hori S, Nomura T, Sakaguchi S. Control of regulatory T cell development by the transcription factor Foxp3. Science 2003;299(5609):1057–61.
  147. 147. Gershon RK, Kondo K. Cell interactions in the induction of tolerance: the role of thymic lymphocytes. Immunology 1970;18(5):723–37.
  148. 148. Paiva RS, Lino AC, Bergman M-L, Caramalho I, Sousa AE, Zelenay S, et al. Recent thymic emigrants are the preferential precursors of regulatory T cells differentiated in the periphery. Proc Natl Acad Sci U S A 2013;110(16):6494–9.
  149. 149. Curotto de Lafaille MA, Lafaille JJ. Natural and adaptive foxp3+ regulatory T cells: more of the same or a division of labor? Immunity 2009;30(5):626–35.
  150. 150. Picarda E, Bézie S, Venturi V, Echasserieau K, Mérieau E, Delhumeau A, et al. MHC-derived allopeptide activates TCR-biased CD8+ Tregs and suppresses organ rejection. J Clin Invest. 2014;124(6):2497–512.
  151. 151. Shimizu J, Yamazaki S, Takahashi T, Ishida Y, Sakaguchi S. Stimulation of CD25(+)CD4(+) regulatory T cells through GITR breaks immunological self-tolerance. Nat Immunol. 2002;3(2):135–42.
  152. 152. Takahashi T, Tagami T, Yamazaki S, Uede T, Shimizu J, Sakaguchi N, et al. Immunologic self-tolerance maintained by CD25(+)CD4(+) regulatory T cells constitutively expressing cytotoxic T lymphocyte-associated antigen 4. J Exp Med. 2000;192(2):303–10.
  153. 153. Szanya V, Ermann J, Taylor C, Holness C, Fathman CG. The subpopulation of CD4+CD25+ splenocytes that delays adoptive transfer of diabetes expresses L-selectin and high levels of CCR7. J Immunol Baltim Md 1950. 2002;169(5):2461–5.
  154. 154. Huang C-T, Workman CJ, Flies D, Pan X, Marson AL, Zhou G, et al. Role of LAG-3 in regulatory T cells. Immunity 2004;21(4):503–13.
  155. 155. Liu W, Putnam AL, Xu-Yu Z, Szot GL, Lee MR, Zhu S, et al. CD127 expression inversely correlates with FoxP3 and suppressive function of human CD4+ T reg cells. J Exp Med. 2006;203(7):1701–11.
  156. 156. Ligocki AJ, Niederkorn JY. Advances on Non-CD4 + Foxp3+ T regulatory cells: CD8+, type 1, and double negative t regulatory cells in organ transplantation. Transplantation 2015;99(8):1553–9.
  157. 157. Ménoret S, Guillonneau C, Bezié S, Caron L, Anegon I, Li X-L. Phenotypic and functional characterization of CD8(+) T regulatory cells. Methods Mol Biol Clifton NJ. 2011;677:63–83.
  158. 158. Niederkorn JY. Emerging concepts in CD8(+) T regulatory cells. Curr Opin Immunol. 2008;20(3):327–31.
  159. 159. Guillonneau C, Hill M, Hubert F-X, Chiffoleau E, Hervé C, Li X-L, et al. CD40Ig treatment results in allograft acceptance mediated by CD8CD45RC T cells, IFN-gamma, and indoleamine 2,3-dioxygenase. J Clin Invest. 2007;117(4):1096–106.
  160. 160. Guillonneau C, Picarda E, Anegon I. CD8+ regulatory T cells in solid organ transplantation. Curr Opin Organ Transplant. 2010;15(6):751–6.
  161. 161. Fontenot JD, Gavin MA, Rudensky AY. Foxp3 programs the development and function of CD4+CD25+ regulatory T cells. Nat Immunol. 2003;4(4):330–6.
  162. 162. Hori S, Takahashi T, Sakaguchi S. Control of autoimmunity by naturally arising regulatory CD4+ T cells. Adv Immunol. 2003;81:331–71.
  163. 163. Bacchetta R, Passerini L, Gambineri E, Dai M, Allan SE, Perroni L, et al. Defective regulatory and effector T cell functions in patients with FOXP3 mutations. J Clin Invest. 2006;116(6):1713–22.
  164. 164. Morgan ME, van Bilsen JHM, Bakker AM, Heemskerk B, Schilham MW, Hartgers FC, et al. Expression of FOXP3 mRNA is not confined to CD4+CD25+ T regulatory cells in humans. Hum Immunol. 2005;66(1):13–20.
  165. 165. Thornton AM, Korty PE, Tran DQ, Wohlfert EA, Murray PE, Belkaid Y, et al. Expression of Helios, an Ikaros transcription factor family member, differentiates thymic-derived from peripherally induced Foxp3+ T regulatory cells. J Immunol Baltim Md 1950. 2010;184(7):3433–41.
  166. 166. Yadav M, Louvet C, Davini D, Gardner JM, Martinez-Llordella M, Bailey-Bucktrout S, et al. Neuropilin-1 distinguishes natural and inducible regulatory T cells among regulatory T cell subsets in vivo. J Exp Med. 2012;209(10):1713–22, S1–19.
  167. 167. Kim H-J, Barnitz RA, Kreslavsky T, Brown FD, Moffett H, Lemieux ME, et al. Stable inhibitory activity of regulatory T cells requires the transcription factor Helios. Science 2015;350(6258):334–9.
  168. 168. Lee WT, Prasad A, Watson ARO. Anergy in CD4 memory T lymphocytes. II. Abrogation of TCR-induced formation of membrane signaling complexes. Cell Immunol. 2012;276(1-2):26–34.
  169. 169. Mellor AL, Munn DH. IDO expression by dendritic cells: tolerance and tryptophan catabolism. Nat Rev Immunol. 2004;4(10):762–74.
  170. 170. Grossman WJ, Verbsky JW, Tollefsen BL, Kemper C, Atkinson JP, Ley TJ. Differential expression of granzymes A and B in human cytotoxic lymphocyte subsets and T regulatory cells. Blood. 2004;104(9):2840–8.
  171. 171. Deaglio S, Dwyer KM, Gao W, Friedman D, Usheva A, Erat A, et al. Adenosine generation catalyzed by CD39 and CD73 expressed on regulatory T cells mediates immune suppression. J Exp Med. 2007;204(6):1257–65.
  172. 172. Pandiyan P, Zheng L, Ishihara S, Reed J, Lenardo MJ. CD4+CD25+Foxp3+ regulatory T cells induce cytokine deprivation-mediated apoptosis of effector CD4+ T cells. Nat Immunol. 2007;8(12):1353–62.
  173. 173. Bézie S, Picarda E, Ossart J, Tesson L, Usal C, Renaudin K, et al. IL-34 is a Treg-specific cytokine and mediates transplant tolerance. J Clin Invest. 2015;125(10):3952–64.
  174. 174. Chaturvedi V, Collison LW, Guy CS, Workman CJ, Vignali DAA. Cutting edge: human regulatory T cells require IL-35 to mediate suppression and infectious tolerance. J Immunol Baltim Md 1950. 2011;186(12):6661–6.
  175. 175. Chesneau M, Michel L, Dugast E, Chenouard A, Baron D, Pallier A, et al. Tolerant kidney transplant patients produce b cells with regulatory properties. J Am Soc Nephrol JASN. 2015;26(10):2588–98.
  176. 176. Bézie S, Picarda E, Ossart J, Martinet B, Anegon I, Guillonneau C. Compensatory regulatory networks between CD8 T, B, and myeloid cells in organ transplantation tolerance. J Immunol Baltim Md 1950. 2015;195(12):5805–15.
  177. 177. Durand J, Chiffoleau E. B cells with regulatory properties in transplantation tolerance. World J Transplant. 2015;5(4):196–208.
  178. 178. Dugast A-S, Haudebourg T, Coulon F, Heslan M, Haspot F, Poirier N, et al. Myeloid-derived suppressor cells accumulate in kidney allograft tolerance and specifically suppress effector T cell expansion. J Immunol Baltim Md 1950. 2008;180(12):7898–906.
  179. 179. Dilek N, Poirier N, Usal C, Martinet B, Blancho G, Vanhove B. Control of transplant tolerance and intragraft regulatory T cell localization by myeloid-derived suppressor cells and CCL5. J Immunol Baltim Md 1950. 2012;188(9):4209–16.
  180. 180. Pallier A, Hillion S, Danger R, Giral M, Racapé M, Degauque N, et al. Patients with drug-free long-term graft function display increased numbers of peripheral B cells with a memory and inhibitory phenotype. Kidney Int. 2010;78(5):503–13.
  181. 181. Newell KA, Asare A, Kirk AD, Gisler TD, Bourcier K, Suthanthiran M, et al. Identification of a B cell signature associated with renal transplant tolerance in humans. J Clin Invest. 2010;120(6):1836–47.
  182. 182. Mauri C, Blair PA. Regulatory B cells in autoimmunity: developments and controversies. Nat Rev Rheumatol. 2010;6(11):636–43.
  183. 183. Le Texier L, Thebault P, Lavault A, Usal C, Merieau E, Quillard T, et al. Long-term allograft tolerance is characterized by the accumulation of B cells exhibiting an inhibited profile. Am J Transplant Off J Am Soc Transplant Am Soc Transpl Surg. 2011;11(3):429–38.
  184. 184. Bouaziz J-D, Le Buanec H, Saussine A, Bensussan A, Bagot M. IL-10 producing regulatory B cells in mice and humans: state of the art. Curr Mol Med. 2012;12(5):519–27.
  185. 185. Qian L, Qian C, Chen Y, Bai Y, Bao Y, Lu L, et al. Regulatory dendritic cells program B cells to differentiate into CD19hiFcγIIbhi regulatory B cells through IFN-β and CD40L. Blood. 2012;120(3):581–91.
  186. 186. Fillatreau S, Gray D, Anderton SM. Not always the bad guys: B cells as regulators of autoimmune pathology. Nat Rev Immunol. 2008;8(5):391–7.
  187. 187. Yanaba K, Bouaziz J-D, Matsushita T, Tsubata T, Tedder TF. The development and function of regulatory B cells expressing IL-10 (B10 cells) requires antigen receptor diversity and TLR signals. J Immunol Baltim Md 1950. 2009;182(12):7459–72.
  188. 188. Blair PA, Noreña LY, Flores-Borja F, Rawlings DJ, Isenberg DA, Ehrenstein MR, et al. CD19(+)CD24(hi)CD38(hi) B cells exhibit regulatory capacity in healthy individuals but are functionally impaired in systemic Lupus Erythematosus patients. Immunity 2010;32(1):129–40.
  189. 189. Durand J, Huchet V, Merieau E, Usal C, Chesneau M, Remy S, et al. Regulatory B Cells with a Partial Defect in CD40 Signaling and Overexpressing Granzyme B Transfer Allograft Tolerance in Rodents. J Immunol Baltim Md 1950. 2015;195(10):5035–44.
  190. 190. Kim JI, Rothstein DM, Markmann JF. Role of B cells in tolerance induction. Curr Opin Organ Transplant. 2015;20(4):369–75.
  191. 191. Deng S, Moore DJ, Huang X, Lian M-M, Mohiuddin M, Velededeoglu E, et al. Cutting edge: transplant tolerance induced by anti-CD45RB requires B lymphocytes. J Immunol Baltim Md 1950. 2007 May 15;178(10):6028–32.
  192. 192. Darrasse-Jèze G, Deroubaix S, Mouquet H, Victora GD, Eisenreich T, Yao K, et al. Feedback control of regulatory T cell homeostasis by dendritic cells in vivo. J Exp Med. 2009;206(9):1853–62.
  193. 193. Manicassamy S, Pulendran B. Dendritic cell control of tolerogenic responses. Immunol Rev. 2011;241(1):206–27.
  194. 194. Maldonado RA, von Andrian UH. How tolerogenic dendritic cells induce regulatory T cells. Adv Immunol. 2010;108:111–65.
  195. 195. Moreau A, Varey E, Bouchet-Delbos L, Cuturi M-C. Cell therapy using tolerogenic dendritic cells in transplantation. Transplant Res. 2012;1(1):13.
  196. 196. Fu F, Li Y, Qian S, Lu L, Chambers F, Starzl TE, et al. Costimulatory molecule-deficient dendritic cell progenitors (MHC class II+, CD80dim, CD86-) prolong cardiac allograft survival in nonimmunosuppressed recipients. Transplantation 1996;62(5):659–65.
  197. 197. Lutz MB, Suri RM, Niimi M, Ogilvie AL, Kukutsch NA, Rössner S, et al. Immature dendritic cells generated with low doses of GM-CSF in the absence of IL-4 are maturation resistant and prolong allograft survival in vivo. Eur J Immunol. 2000;30(7):1813–22.
  198. 198. Hill M, Thebault P, Segovia M, Louvet C, Bériou G, Tilly G, et al. Cell therapy with autologous tolerogenic dendritic cells induces allograft tolerance through interferon-gamma and epstein-barr virus-induced gene 3. Am J Transplant Off J Am Soc Transplant Am Soc Transpl Surg. 2011;11(10):2036–45.
  199. 199. Segovia M, Louvet C, Charnet P, Savina A, Tilly G, Gautreau L, et al. Autologous dendritic cells prolong allograft survival through Tmem176b-dependent antigen cross-presentation. Am J Transplant Off J Am Soc Transplant Am Soc Transpl Surg. 2014;14(5):1021–31.
  200. 200. Chauveau C, Rémy S, Royer PJ, Hill M, Tanguy-Royer S, Hubert F-X, et al. Heme oxygenase-1 expression inhibits dendritic cell maturation and proinflammatory function but conserves IL-10 expression. Blood 2005;106(5):1694–702.
  201. 201. Rogers NM, Isenberg JS, Thomson AW. Plasmacytoid dendritic cells: no longer an enigma and now key to transplant tolerance? Am J Transplant Off J Am Soc Transplant Am Soc Transpl Surg. 2013;13(5):1125–33.
  202. 202. Li XL, Ménoret S, Bezie S, Caron L, Chabannes D, Hill M, et al. Mechanism and localization of CD8 regulatory T cells in a heart transplant model of tolerance. J Immunol Baltim Md 1950. 2010;185(2):823–33.
  203. 203. Ochando JC, Homma C, Yang Y, Hidalgo A, Garin A, Tacke F, et al. Alloantigen-presenting plasmacytoid dendritic cells mediate tolerance to vascularized grafts. Nat Immunol. 2006;7(6):652–62.
  204. 204. Moseman EA, Liang X, Dawson AJ, Panoskaltsis-Mortari A, Krieg AM, Liu Y-J, et al. Human plasmacytoid dendritic cells activated by CpG oligodeoxynucleotides induce the generation of CD4+CD25+ regulatory T cells. J Immunol Baltim Md 1950. 2004;173(7):4433–42.
  205. 205. Boor PPC, Metselaar HJ, Jonge S de, Mancham S, van der Laan LJW, Kwekkeboom J. Human plasmacytoid dendritic cells induce CD8+ LAG-3+ Foxp3+ CTLA-4+ regulatory T cells that suppress allo-reactive memory T cells. Eur J Immunol. 2011;41(6):1663–74.
  206. 206. Gilliet M, Liu Y-J. Generation of human CD8 T regulatory cells by CD40 ligand-activated plasmacytoid dendritic cells. J Exp Med. 2002;195(6):695–704.
  207. 207. Tokita D, Mazariegos GV, Zahorchak AF, Chien N, Abe M, Raimondi G, et al. High PD-L1/CD86 ratio on plasmacytoid dendritic cells correlates with elevated T-regulatory cells in liver transplant tolerance. Transplantation 2008;85(3):369–77.
  208. 208. Manavalan JS, Kim-Schulze S, Scotto L, Naiyer AJ, Vlad G, Colombo PC, et al. Alloantigen specific CD8+CD28- FOXP3+ T suppressor cells induce ILT3+ ILT4+ tolerogenic endothelial cells, inhibiting alloreactivity. Int Immunol. 2004;16(8):1055–68.
  209. 209. Chiffoleau E, Bériou G, Dutartre P, Usal C, Soulillou J-P, Cuturi MC. Role for thymic and splenic regulatory CD4+ T cells induced by donor dendritic cells in allograft tolerance by LF15-0195 treatment. J Immunol Baltim Md 1950. 2002;168(10):5058–69.
  210. 210. Degauque N, Lair D, Dupont A, Moreau A, Roussey G, Moizant F, et al. Dominant tolerance to kidney allografts induced by anti-donor MHC class II antibodies: cooperation between T and non-T CD103+ cells. J Immunol Baltim Md 1950. 2006;176(7):3915–22.
  211. 211. Josien R, Heslan M, Brouard S, Soulillou JP, Cuturi MC. Critical requirement for graft passenger leukocytes in allograft tolerance induced by donor blood transfusion. Blood 1998;92(12):4539–44.
  212. 212. Broichhausen C, Riquelme P, Geissler EK and Hutchinson JA. Regulatory macrophages as therapeutic targets and therapeutic agents in solid organ transplantation. Curr. Opin. Organ Transplant. 2012;17(4):332–342.
  213. 213. Elhage R, Cheraï M, Levacher B, Darrasse-Jeze G, Baillou C, Zhao X, et al. C-terminal cleavage of human Foxp3 at a proprotein convertase motif abrogates its suppressive function. Scand J Immunol. 2015;81(4):229–39.
  214. 214. Liu G, Duan K, Ma H, Niu Z, Peng J, Zhao Y. An instructive role of donor macrophages in mixed chimeras in the induction of recipient CD4(+)Foxp3(+) Treg cells. Immunol Cell Biol. 2011;89(8):827–35.
  215. 215. Hashimoto D, Chow A, Greter M, Saenger Y, Kwan W-H, Leboeuf M, et al. Pretransplant CSF-1 therapy expands recipient macrophages and ameliorates GVHD after allogeneic hematopoietic cell transplantation. J Exp Med. 2011;208(5):1069–82.
  216. 216. Wood KJ, Bushell A, Hester J. Regulatory immune cells in transplantation. Nat Rev Immunol. 2012;12(6):417–30.
  217. 217. Darrasse-Jèze G, Darasse-Jèze G, Klatzmann D, Charlotte F, Salomon BL, Cohen JL. CD4+CD25+ regulatory/suppressor T cells prevent allogeneic fetus rejection in mice. Immunol Lett. 2006;102(1):106–9.
  218. 218. Taieb J, Chaput N, Schartz N, Roux S, Novault S, Ménard C, et al. Chemoimmunotherapy of tumors: cyclophosphamide synergizes with exosome based vaccines. J Immunol Baltim Md 1950. 2006;176(5):2722–9.
  219. 219. Dilek N, Vuillefroy de Silly R, Blancho G, Vanhove B. Myeloid-derived suppressor cells: mechanisms of action and recent advances in their role in transplant tolerance. Front Immunol. 2012;3:208.
  220. 220. Dilek N, van Rompaey N, Le Moine A, Vanhove B. Myeloid-derived suppressor cells in transplantation. Curr Opin Organ Transplant. 2010;15(6):765–8.
  221. 221. Jiang S, Lechler RI, He X-S, Huang J-F. Regulatory T cells and transplantation tolerance. Hum Immunol. 2006;67(10):765–76.
  222. 222. Ordonez L, Bernard I, L’faqihi-Olive F-E, Tervaert JWC, Damoiseaux J, Saoudi A. CD45RC isoform expression identifies functionally distinct T cell subsets differentially distributed between healthy individuals and AAV patients. PloS One 2009;4(4):e5287.
  223. 223. Kamanaka M, Huber S, Zenewicz LA, Gagliani N, Rathinam C, O’Connor W, et al. Memory/effector (CD45RB(lo)) CD4 T cells are controlled directly by IL-10 and cause IL-22-dependent intestinal pathology. J Exp Med. 2011;208(5):1027–40.
  224. 224. Fecteau S, Basadonna GP, Freitas A, Ariyan C, Sayegh MH, Rothstein DM. CTLA-4 up-regulation plays a role in tolerance mediated by CD45. Nat Immunol. 2001;2(1):58–63.
  225. 225. Auersvald LA, Rothstein DM, Oliveira SC, Khuong CQ, Basadonna GP. Anti-CD45RB treatment prolongs islet allograft survival in mice. Transplant Proc. 1997;29(1–2):771.
  226. 226. Moreau A, Hill M, Thébault P, Deschamps JY, Chiffoleau E, Chauveau C, et al. Tolerogenic dendritic cells actively inhibit T cells through heme oxygenase-1 in rodents and in nonhuman primates. FASEB J. 2009;23(9):3070–7.
  227. 227. Spickett GP, Brandon MR, Mason DW, Williams AF, Woollett GR. MRC OX-22, a monoclonal antibody that labels a new subset of T lymphocytes and reacts with the high molecular weight form of the leukocyte-common antigen. J Exp Med. 1983;158(3):795–810.
  228. 228. Xystrakis E, Bernard I, Dejean AS, Alsaati T, Druet P, Saoudi A. Alloreactive CD4 T lymphocytes responsible for acute and chronic graft-versus-host disease are contained within the CD45RChigh but not the CD45RClow subset. Eur J Immunol. 2004;34(2):408–17.
  229. 229. Xystrakis E, Dejean AS, Bernard I, Druet P, Liblau R, Gonzalez-Dunia D, et al. Identification of a novel natural regulatory CD8 T-cell subset and analysis of its mechanism of regulation. Blood 2004;104(10):3294–301.
  230. 230. Powrie F, Mason D. OX-22high CD4+ T cells induce wasting disease with multiple organ pathology: prevention by the OX-22low subset. J Exp Med. 1990;172(6):1701–8.
  231. 231. Laskowski IA, Pratschke J, Wilhelm MJ, Dong VM, Beato F, Taal M, et al. Anti-CD28 monoclonal antibody therapy prevents chronic rejection of renal allografts in rats. J Am Soc Nephrol JASN. 2002;13(2):519–27.
  232. 232. Cobbold SP, Adams E, Marshall SE, Davies JD, Waldmann H. Mechanisms of peripheral tolerance and suppression induced by monoclonal antibodies to CD4 and CD8. Immunol Rev. 1996;149:5–33.
  233. 233. Qin S, Cobbold SP, Pope H, Elliott J, Kioussis D, Davies J, et al. “Infectious” transplantation tolerance. Science 1993;259(5097):974–7.
  234. 234. Rothstein DM, Livak MF, Kishimoto K, Ariyan C, Qian HY, Fecteau S, et al. Targeting signal 1 through CD45RB synergizes with CD40 ligand blockade and promotes long term engraftment and tolerance in stringent transplant models. J Immunol Baltim Md 1950. 2001;166(1):322–9.
  235. 235. Biomarkers Definitions Working Group. Biomarkers and surrogate endpoints: preferred definitions and conceptual framework. Clin Pharmacol Ther. 2001;69(3):89–95.
  236. 236. Costanzo MR, Dipchand A, Starling R, Anderson A, Chan M, Desai S, et al. The International Society of Heart and Lung Transplantation Guidelines for the care of heart transplant recipients. J Heart Lung Transplant Off Publ Int Soc Heart Transplant. 2010;29(8):914–56.
  237. 237. Bonnemains L, Cherifi A, Girerd N, Odille F, Felblinger J. Design of the DRAGET Study: a multicentre controlled diagnostic study to assess the detection of acute rejection in patients with heart transplant by means of T2 quantification with MRI in comparison to myocardial biopsies. BMJ Open. 2015;5(10):e008963.
  238. 238. Foucher Y, Daguin P, Akl A, Kessler M, Ladrière M, Legendre C, et al. A clinical scoring system highly predictive of long-term kidney graft survival. Kidney Int. 2010;78(12):1288–94.
  239. 239. Brouard S, Mansfield E, Braud C, Li L, Giral M, Hsieh S, et al. Identification of a peripheral blood transcriptional biomarker panel associated with operational renal allograft tolerance. Proc Natl Acad Sci U S A 2007;104(39):15448–53.
  240. 240. Sagoo P, Perucha E, Sawitzki B, Tomiuk S, Stephens DA, Miqueu P, et al. Development of a cross-platform biomarker signature to detect renal transplant tolerance in humans. J Clin Invest. 2010;120(6):1848–61.
  241. 241. Moraes-Vieira PMM, Takenaka MCS, Silva HM, Monteiro SM, Agena F, Lemos F, et al. GATA3 and a dominant regulatory gene expression profile discriminate operational tolerance in human transplantation. Clin Immunol Orlando Fla. 2012;142(2):117–26.
  242. 242. Braza F, Dugast E, Panov I, Paul C, Vogt K, Pallier A, et al. Central role of CD45RA- Foxp3hi memory regulatory T cells in clinical kidney transplantation tolerance. J Am Soc Nephrol JASN. 2015;26(8):1795–805.
  243. 243. Moraes-Vieira PMM, Silva HM, Takenaka MCS, Monteiro SM, Lemos F, Saitovitch D, et al. Differential monocyte STAT6 activation and CD4(+)CD25(+)Foxp3(+) T cells in kidney operational tolerance transplanted individuals. Hum Immunol. 2010;71(5):442–50.
  244. 244. Martínez-Llordella M, Puig-Pey I, Orlando G, Ramoni M, Tisone G, Rimola A, et al. Multiparameter immune profiling of operational tolerance in liver transplantation. Am J Transplant Off J Am Soc Transplant Am Soc Transpl Surg. 2007;7(2):309–19.
  245. 245. Braza F, Soulillou J-P, Brouard S. Gene expression signature in transplantation tolerance. Clin Chim Acta Int J Clin Chem. 2012;413(17–18):1414–8.
  246. 246. Bohne F, Martínez-Llordella M, Lozano J-J, Miquel R, Benítez C, Londoño M-C, et al. Intra-graft expression of genes involved in iron homeostasis predicts the development of operational tolerance in human liver transplantation. J Clin Invest. 2012;122(1):368–82.
  247. 247. Streitz M, Miloud T, Kapinsky M, Reed MR, Magari R, Geissler EK, et al. Standardization of whole blood immune phenotype monitoring for clinical trials: panels and methods from the ONE study. Transplant Res. 2013;2(1):17.
  248. 248. Bézie S, Picarda E, Tesson L, Renaudin K, Durand J, Ménoret S, et al. Fibrinogen-like protein 2/fibroleukin induces long-term allograft survival in a rat model through regulatory B cells. PloS One 2015;10(3):e0119686.
  249. 249. Gielis EM, Ledeganck KJ, De Winter BY, Del Favero J, Bosmans J-L, Claas FHJ, et al. Cell-Free DNA: An Upcoming Biomarker in Transplantation. Am J Transplant Off J Am Soc Transplant Am Soc Transpl Surg. 2015;15(10):2541–51.
  250. 250. Afaneh C, Muthukumar T, Lubetzky M, Ding R, Snopkowski C, Sharma VK, et al. Urinary cell levels of mRNA for OX40, OX40L, PD-1, PD-L1, or PD-L2 and acute rejection of human renal allografts. Transplantation 2010;90(12):1381–7.
  251. 251. Bodonyi-Kovacs G, Strom TB, Putheti P. A20--a biomarker of allograft outcome: a showcase in kidney transplantation. Adv Exp Med Biol. 2014;809:103–16.
  252. 252. Manfro RC, Aquino-Dias EC, Joelsons G, Nogare AL, Carpio VN, Gonçalves LFS. Noninvasive Tim-3 messenger RNA evaluation in renal transplant recipients with graft dysfunction. Transplantation 2008;86(12):1869–74.
  253. 253. Bertoni E, Larti A, Rosso G, Zanazzi M, Di Maria L, Salvadori M. Good outcomes with cyclosporine very low exposure with everolimus high exposure in renal transplant patients. J Nephrol. 2011;24(5):613–8.
  254. 254. Guillonneau C, Hill M, Hubert F-X, Chiffoleau E, Hervé C, Li X-L, et al. CD40Ig treatment results in allograft acceptance mediated by CD8CD45RC T cells, IFN-gamma, and indoleamine 2,3-dioxygenase. J Clin Invest. 2007;117(4):1096–106.
  255. 255. Kim B-S, Nishikii H, Baker J, Pierini A, Schneidawind D, Pan Y, et al. Treatment with agonistic DR3 antibody results in expansion of donor Tregs and reduced graft-versus-host disease. Blood 2015;126(4):546–57.
  256. 256. Vincenti F, Larsen C, Durrbach A, Wekerle T, Nashan B, Blancho G, et al. Costimulation blockade with belatacept in renal transplantation. N Engl J Med. 2005;353(8):770–81.
  257. 257. Trzonkowski P, Bieniaszewska M, Juścińska J, Dobyszuk A, Krzystyniak A, Marek N, et al. First-in-man clinical results of the treatment of patients with graft versus host disease with human ex vivo expanded CD4+CD25+CD127- T regulatory cells. Clin Immunol Orlando Fla. 2009;133(1):22–6.
  258. 258. Brunstein CG, Miller JS, Cao Q, McKenna DH, Hippen KL, Curtsinger J, et al. Infusion of ex vivo expanded T regulatory cells in adults transplanted with umbilical cord blood: safety profile and detection kinetics. Blood 2011;117(3):1061–70.
  259. 259. Di Ianni M, Falzetti F, Carotti A, Terenzi A, Castellino F, Bonifacio E, et al. Tregs prevent GVHD and promote immune reconstitution in HLA-haploidentical transplantation. Blood 2011;117(14):3921–8.
  260. 260. Martelli MF, Di Ianni M, Ruggeri L, Falzetti F, Carotti A, Terenzi A, et al. HLA-haploidentical transplantation with regulatory and conventional T-cell adoptive immunotherapy prevents acute leukemia relapse. Blood 2014;124(4):638–44.
  261. 261. Bacchetta R, Lucarelli B, Sartirana C, Gregori S, Lupo Stanghellini MT, Miqueu P, et al. Immunological outcome in haploidentical-HSC transplanted patients treated with IL-10-anergized donor T cells. Front Immunol. 2014;5:16.
  262. 262. Moreau A, Varey E, Bouchet-Delbos L, Cuturi M-C. Cell therapy using tolerogenic dendritic cells in transplantation. Transplant Res. 2012;1(1):13.
  263. 263. Tobin LM, Healy ME, English K, Mahon BP. Human mesenchymal stem cells suppress donor CD4(+) T cell proliferation and reduce pathology in a humanized mouse model of acute graft-versus-host disease. Clin Exp Immunol. 2013;172(2):333–48.
  264. 264. Petrelli A, Tresoldi E, Mfarrej BG, Paganelli A, Spotti D, Caldara R, et al. Generation of donor-specific T regulatory type 1 cells from patients on dialysis for cell therapy after kidney transplantation. Transplantation 2015;99(8):1582–9.
  265. 265. Geissler EK. The ONE Study compares cell therapy products in organ transplantation: introduction to a review series on suppressive monocyte-derived cells. Transplant Res. 2012;1(1):11.
  266. 266. Zheng J, Liu Y, Liu Y, Liu M, Xiang Z, Lam K-T, et al. Human CD8+ regulatory T cells inhibit GVHD and preserve general immunity in humanized mice. Sci Transl Med. 2013;5(168):168ra9.
  267. 267. Picarda É, Ossart J, Bézie S, Guillonneau C. [Key role of allopeptide-specific CD8(+) Tregs in transplantation]. Médecine Sci MS. 2015;31(1):22–4.
  268. 268. Dai Z, Zhang S, Xie Q, Wu S, Su J, Li S, et al. Natural CD8+CD122+ T cells are more potent in suppression of allograft rejection than CD4+CD25+ regulatory T cells. Am J Transplant Off J Am Soc Transplant Am Soc Transpl Surg. 2014;14(1):39–48.
  269. 269. Nouël A, Simon Q, Jamin C, Pers J-O, Hillion S. Regulatory B cells: an exciting target for future therapeutics in transplantation. Front Immunol. 2014;5:11.
  270. 270. Tang Q, Lee K. Regulatory T-cell therapy for transplantation: how many cells do we need? Curr Opin Organ Transplant. 2012;17(4):349–54.
  271. 271. Nguyen VH, Zeiser R, Dasilva DL, Chang DS, Beilhack A, Contag CH, et al. In vivo dynamics of regulatory T-cell trafficking and survival predict effective strategies to control graft-versus-host disease following allogeneic transplantation. Blood 2007;109(6):2649–56.
  272. 272. Nadig SN, Wieckiewicz J, Wu DC, Warnecke G, Zhang W, Luo S, et al. In vivo prevention of transplant arteriosclerosis by ex vivo-expanded human regulatory T cells. Nat Med. 2010;16(7):809–13.
  273. 273. Issa F, Hester J, Goto R, Nadig SN, Goodacre TE, Wood K. Ex vivo-expanded human regulatory T cells prevent the rejection of skin allografts in a humanized mouse model. Transplantation 2010;90(12):1321–7.
  274. 274. Wu DC, Hester J, Nadig SN, Zhang W, Trzonkowski P, Gray D, et al. Ex vivo expanded human regulatory T cells can prolong survival of a human islet allograft in a humanized mouse model. Transplantation 2013;96(8):707–16.
  275. 275. Sagoo P, Ali N, Garg G, Nestle FO, Lechler RI, Lombardi G. Human regulatory T cells with alloantigen specificity are more potent inhibitors of alloimmune skin graft damage than polyclonal regulatory T cells. Sci Transl Med. 2011;3(83):83ra42.
  276. 276. Veerapathran A, Pidala J, Beato F, Yu X-Z, Anasetti C. Ex vivo expansion of human Tregs specific for alloantigens presented directly or indirectly. Blood 2011;118(20):5671–80.
  277. 277. Tang Q, Bluestone JA. Regulatory T-cell therapy in transplantation: moving to the clinic. Cold Spring Harb Perspect Med. 2013;3(11) a015552
  278. 278. Cheraï M, Hamel Y, Baillou C, Touil S, Guillot-Delost M, Charlotte F, et al. Generation of human alloantigen-specific regulatory T-cells under good manufacturing practice-compliant conditions for cell therapy. Cell Transplant 2015;24(12):2527–40.
  279. 279. Putnam AL, Safinia N, Medvec A, Laszkowska M, Wray M, Mintz MA, et al. Clinical grade manufacturing of human alloantigen-reactive regulatory T cells for use in transplantation. Am J Transplant Off J Am Soc Transplant Am Soc Transpl Surg. 2013;13(11):3010–20.
  280. 280. Peters JH, Hilbrands LB, Koenen HJPM, Joosten I. Ex vivo generation of human alloantigen-specific regulatory T cells from CD4(pos)CD25(high) T cells for immunotherapy. PloS One 2008;3(5):e2233.
  281. 281. Qin S, Cobbold SP, Pope H, Elliott J, Kioussis D, Davies J, et al. “Infectious” transplantation tolerance. Science 1993;259(5097):974–7.
  282. 282. Noyan F, Lee Y-S, Zimmermann K, Hardtke-Wolenski M, Taubert R, Warnecke G, et al. Isolation of human antigen-specific regulatory T cells with high suppressive function. Eur J Immunol. 2014;44(9):2592–602.
  283. 283. Veerapathran A, Pidala J, Beato F, Betts B, Kim J, Turner JG, et al. Human regulatory T cells against minor histocompatibility antigens: ex vivo expansion for prevention of graft-versus-host disease. Blood 2013;122(13):2251–61.
  284. 284. Sangiolo D. Redirected T cells in cancer therapy. Expert Opin Biol Ther. 2015;15(12):1667–70.
  285. 285. Duong CPM, Yong CSM, Kershaw MH, Slaney CY, Darcy PK. Cancer immunotherapy utilizing gene-modified T cells: From the bench to the clinic. Mol Immunol. 2015;67(2 Pt A):46–57.
  286. 286. Baron U, Floess S, Wieczorek G, Baumann K, Grützkau A, Dong J, et al. DNA demethylation in the human FOXP3 locus discriminates regulatory T cells from activated FOXP3(+) conventional T cells. Eur J Immunol. 2007;37(9):2378–89.
  287. 287. Allan SE, Crome SQ, Crellin NK, Passerini L, Steiner TS, Bacchetta R, et al. Activation-induced FOXP3 in human T effector cells does not suppress proliferation or cytokine production. Int Immunol. 2007;19(4):345–54.
  288. 288. Scottà C, Fanelli G, Hoong SJ, Romano M, Lamperti EN, Sukthankar M, et al. Impact of immunosuppressive drugs on the therapeutic efficacy of ex vivo expanded human regulatory T cells. Haematologica. 2016;101(1):91–100.
  289. 289. Hester J, Schiopu A, Nadig SN, Wood KJ. Low-dose rapamycin treatment increases the ability of human regulatory T cells to inhibit transplant arteriosclerosis in vivo. Am J Transplant Off J Am Soc Transplant Am Soc Transpl Surg. 2012;12(8):2008–16.
  290. 290. Scottà C, Esposito M, Fazekasova H, Fanelli G, Edozie FC, Ali N, et al. Differential effects of rapamycin and retinoic acid on expansion, stability and suppressive qualities of human CD4(+)CD25(+)FOXP3(+) T regulatory cell subpopulations. Haematologica 2013;98(8):1291–9.
  291. 291. Hippen KL, Merkel SC, Schirm DK, Nelson C, Tennis NC, Riley JL, et al. Generation and large-scale expansion of human inducible regulatory T cells that suppress graft-versus-host disease. Am J Transplant Off J Am Soc Transplant Am Soc Transpl Surg. 2011;11(6):1148–57.
  292. 292. Coenen JJA, Koenen HJPM, van Rijssen E, Kasran A, Boon L, Hilbrands LB, et al. Rapamycin, not cyclosporine, permits thymic generation and peripheral preservation of CD4+ CD25+ FoxP3+ T cells. Bone Marrow Transplant. 2007;39(9):537–45.
  293. 293. Wu T, Zhang L, Xu K, Sun C, Lei T, Peng J, et al. Immunosuppressive drugs on inducing Ag-specific CD4(+)CD25(+)Foxp3(+) Treg cells during immune response in vivo. Transpl Immunol. 2012;27(1):30–8.

Written By

Laetitia Boucault, Séverine Bézie, Jason Ossart and Carole Guillonneau

Submitted: October 21st, 2015 Reviewed: February 22nd, 2016 Published: September 7th, 2016