Tolerance in Organ Transplantation

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

Tranilast, an analogue of tryptophan catabolites, induces allograft tolerance by CD161+ cells

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Immunosuppressive role of fibrinogen-like protein 2 (FGL2) in CD8+regulatory T cells-mediated long-term graft survival

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In Vitro and In Vivo Assessment of T, B and Myeloid Cells Suppressive Activity and Humoral Responses from Transplant Recipients

International audienceThe main concern in transplantation is to achieve specific tolerance through induction of regulatory cells. The understanding of tolerance mechanisms requires reliable models. Here, we describe models of tolerance to cardiac allograft in rat, induced by blockade of costimulation signals or by upregulation of immunoregulatory molecules through gene transfer. Each of these models allowed in vivo generation of regulatory cells such as regulatory T cells (Tregs), regulatory B cells (Bregs) or regulatory myeloid cells (RegMCs). In this manuscript, we describe two complementary protocols that have been used to identify and define in vitro and in vivo regulatory cell activity to determine their responsibility in tolerance induction and maintenance. First, an in vitro suppressive assay allowed rapid identification of cells with suppressive capacity on effector immune responses in a dose dependent manner, and can be used for further analysis such as cytokine measurement or cytotoxicity. Second, the adoptive transfer of cells from a tolerant treated recipient to a newly irradiated grafted recipient, highlighted the tolerogenic properties of these cells in controlling graft directed immune responses and/or converting new regulatory cells (termed infectious tolerance). These methods are not restricted to cells with known phenotypic markers and can be extended to any cell population. Furthermore, donor directed allospecificity of regulatory cells (an important goal in the field) can be assessed by using third party donor cells or graft either in vitro or in vivo. Finally, to determine the specific tolerogenic capacity of these regulatory cells, we provide protocols to assess the humoral anti-donor antibody responses and the capacity of the recipient to develop humoral responses against new or former known antigens. The models of tolerance described can be used to further characterize regulatory cells, to identify new biomarkers, and immunoregulatory molecules, and are adaptable to other transplantation models or autoimmune diseases in rodent or human

Advances on CD8+ Treg Cells and Their Potential in Transplantation

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Immunoregulatory properties of the cytokine IL-34

International audienceInterleukin-34 is a cytokine with only partially understood functions, described for the first time in 2008. Although IL-34 shares very little homology with CSF-1 (CSF1, M-CSF), they share a common receptor CSF-1R (CSF-1R) and IL-34 has also two distinct receptors (PTP-ζ) and CD138 (syndecan-1). To make the situation more complex, IL-34 has also been shown as pairing with CSF-1 to form a heterodimer. Until now, studies have demonstrated that this cytokine is released by some tissues that differ to those where CSF-1 is expressed and is involved in the differentiation and survival of macrophages, monocytes, and dendritic cells in response to inflammation. The involvement of IL-34 has been shown in areas as diverse as neuronal protection, autoimmune diseases, infection, cancer, and transplantation. Our recent work has demonstrated a new and possible therapeutic role for IL-34 as a Foxp3+ Treg-secreted cytokine mediator of transplant tolerance. In this review, we recapitulate most recent findings on IL-34 and its controversial effects on immune responses and address its immunoregulatory properties and the potential of targeting this cytokine in human

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

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Genetic engineering of human and mouse CD4+ and CD8+ Tregs using lentiviral vectors encoding chimeric antigen receptors

International audienceThe last decade has seen a significant increase of cell therapy protocols using effector T cells (Teffs) in particular, but also, more recently, non-engineered and expanded polyclonal regulatory T cells (Tregs) to control pathological immune responses such as cancer, autoimmune diseases, or transplantation rejection. However, limitations, such as stability, migration, and specificity of the cell products, have been seen. Thus, genetic engineering of these cell subsets is expected to provide the next generation of T cell therapy products. Lentiviral vectors are commonly used to modify Teffs; however, Tregs are more sensitive to mechanical stress and require specific culture conditions. Also, there is a lack of reproducible and efficient protocols to expand and genetically modify Tregs without affecting their growth and function. Due to smaller number of cells and poorer viability upon culture in vitro, mouse Tregs are more difficult to transduce and amplify in vitro than human Tregs. Here we propose a step-by-step protocol to produce both human and mouse genetically modified CD8+ and CD4+ Tregs in sufficient amounts to assess their therapeutic efficacy in humanized immunocompromised mouse models and murine models of disease and to establish pre-clinical proofs of concept. We report, for the first time, an efficient and reproducible method to isolate Tregs from human blood or mouse spleen, transduce with a lentiviral vector, and culture, in parallel, CD8+ and CD4+ Tregs while preserving their function. Beyond chimeric antigen receptor (CAR)-Treg cell therapy, this protocol will promote the development of potential new engineered T cell therapies to treat autoimmune diseases and transplantation rejection

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

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