Inhibition of thrombin on endothelium enhances recruitment of regulatory T cells during IRI and when combined with adoptive Treg transfer, significantly protects against acute tissue injury and prolongs allograft survival

Ischemia-reperfusion injury (IRI) amplifies T cell alloimmune responses after transplantation with thrombin playing a key pro-inflammatory role. To explore the influence of thrombin on regulatory T cell recruitment and efficacy we used a well-established model of IRI in the native murine kidney. Administration of the cytotopic thrombin inhibitor PTL060 inhibited IRI, and by skewing expression of chemokines (reducing CCL2 and CCL3 but increasing CCL17 and CCL22) increased the infiltration of M2 macrophages and Tregs. When PTL060 was combined with infusion of additional Tregs, these effects were further amplified. To test the benefits of thrombin inhibition in a transplant model, BALB/c hearts were transplanted into B6 mice with or without perfusion with PTL060 in combination with Tregs. Thrombin inhibition or Treg infusion alone led to small increments in allograft survival. However, the combined therapy led to modest graft prolongation by the same mechanisms as in renal IRI; graft survival was accompanied by increased numbers of Tregs and anti inflammatory macrophages, and reduced expression of pro-inflammatory cytokines. While the grafts succumbed to rejection associated with the emergence of alloantibody, these data suggest that thrombin inhibition within the transplant vasculature enhances the efficacy of Treg infusion, a therapy that is currently entering the clinic to promote transplant tolerance

Diversity of gut microflora is required for the generation of B cell with regulatory properties in a skin graft model

B cells have been reported to promote graft rejection through alloantibody production. However, there is growing evidence that B cells can contribute to the maintenance of tolerance. Here, we used a mouse model of MHC-class I mismatched skin transplantation to investigate the contribution of B cells to graft survival. We demonstrate that adoptive transfer of B cells prolongs skin graft survival but only when the B cells were isolated from mice housed in low sterility "conventional" (CV) facilities and not from mice housed in pathogen free facilities (SPF). However, prolongation of skin graft survival was lost when B cells were isolated from IL-10 deficient mice housed in CV facilities. The suppressive function of B cells isolated from mice housed in CV facilities correlated with an anti-inflammatory environment and with the presence of a different gut microflora compared to mice maintained in SPF facilities. Treatment of mice in the CV facility with antibiotics abrogated the regulatory capacity of B cells. Finally, we identified transitional B cells isolated from CV facilities as possessing the regulatory function. These findings demonstrate that B cells, and in particular transitional B cells, can promote prolongation of graft survival, a function dependent on licensing by gut microflora

B lymphocytes contribute to indirect pathway T cell sensitisation via acquisition of extracellular vesicles

B cells have been implicated in transplant rejection via antibody‐mediated mechanisms and more recently by presenting donor‐antigens to T cells. We have shown in patients with chronic antibody‐mediated rejection that B cells control the indirect T cell alloresponses. To understand more about the role of B cells as antigen presenting cells for CD4⁺ T cell with indirect allospecificity, B cells were depleted in C57BL/6 mice, using an anti‐CD20 antibody, prior to receiving MHC‐class I‐mismatched (Kᵈ) skin. The absence of B cells at the time of transplantation prolonged skin graft survival. To study the mechanisms behind this observation, T cells with indirect allospecificity were transferred in mice receiving a Kᵈ skin transplant. T cell proliferation was markedly inhibited in the absence of recipient B cells, suggesting that B cells contribute to indirect pathway sensitisation. Furthermore, we have shown that a possible way in which B cells present alloantigens is via acquisition of MHC‐peptide complexes. Finally, we demonstrate that the addition of B cell depletion to the transfer of Tregs with indirect alloresponse further prolonged skin graft survival. This study supports an important role for B cells in indirect T cell priming and further emphasises the advantage of combination therapies in prolonging transplant survival

Diversity of gut microflora is required for the generation of B cell with regulatory properties in a skin graft model

B cells have been reported to promote grafft rejectfion through alloantfibody productfion. However, there fis growfing evfidence that B cells can contrfibute to the mafintenance off tolerance. Here, we used a mouse model off MHC-class I mfismatched skfin transplantatfion to finvestfigate the contrfibutfion off B cells to grafft survfival. We demonstrate that adoptfive transffer off B cells prolongs skfin grafft survfival but only when the B cells were fisolated ffrom mfice housed fin low sterfilfity “conventfional” (CV) ffacfilfitfies and not ffrom mfice housed fin pathogen ffree ffacfilfitfies (SPF). However, prolongatfion off skfin grafft survfival was lost when B cells were fisolated ffrom IL-10 deficfient mfice housed fin CV ffacfilfitfies. The suppressfive ffunctfion off B cells fisolated ffrom mfice housed fin CV ffacfilfitfies correlated wfith an antfi-finlammatory envfironment and wfith the presence off a dfifferent gut mficrolora compared to mfice mafintafined fin SPF ffacfilfitfies. Treatment off mfice fin the CV ffacfilfity wfith antfibfiotfics abrogated the regulatory capacfity off B cells. Ffinally, we fidentfified transfitfional B cells fisolated ffrom CV ffacfilfitfies as possessfing the regulatory ffunctfion. These findfings demonstrate that B cells, and fin partficular transfitfional B cells, can promote prolongatfion off grafft survfival, a ffunctfion dependent on lficensfing by gut mficrolora

Impact of immunosuppressive drugs on the therapeutic efficacy of ex vivo expanded human regulatory T cells

Immunosuppressive drugs in clinical transplantation are necessary to inhibit the immune response to donor antigens. Although they are effective in controlling acute rejection, they do not prevent long-term transplant loss from chronic rejection. In addition, immunosuppressive drugs have adverse side effects, including increased rate of infections and malignancies. Adoptive cell therapy with human Tregs represents a promising strategy for the induction of transplantation tolerance. Phase I/II clinical trials in transplanted patients are already underway, involving the infusion of Tregs alongside concurrent immunosuppressive drugs. However, it remains to be determined whether the presence of immunosuppressive drugs negatively impacts Treg function and stability. We tested in vitro and in vivo the effects of tacrolimus, mycophenolate and methylprednisolone (major ISDs used in transplantation) on ex vivo expanded, rapamycin-treated human Tregs. The in vitro results showed that these drugs had no effect on phenotype, function and stability of Tregs, although tacrolimus affected the expression of chemokine receptors and IL-10 production. However, viability and proliferative capacity were reduced in a dose-dependent manner by all the three drugs. The in vivo experiments using a humanized mouse model confirmed the in vitro results. However, treatment of mice with only rapamycin maintained the viability, function and proliferative ability of adoptively transferred Tregs. Taken together, our results suggest that the key functions of ex vivo expanded Tregs are not affected by a concurrent immunosuppressive therapy. However, the choice of the drug combination and their timing and dosing should be considered as an essential component to induce and maintain tolerance by Treg

The Potency of Allospecific Tregs Cells Appears to Correlate With T Cell Receptor Functional Avidity

CD4(+) CD25(+) regulatory T cells (T(reg) cells) are an attractive adoptive cell therapy in mediating transplantation tolerance. T-cell receptor (TcR) activation is critical for T(reg) function, suggesting that the TcR avidity of T(reg) cells used in therapy may affect the therapeutic outcome. To address this, we compared the regulatory capacity of T(reg) lines expressing TcRs derived from two TcR transgenic mice shown to have the same specificity but different functional avidities. T(reg) lines generated from CD4(+)CD25(+) T cells from C57BL/6 mice were transduced with one of either of these TcRs. The antigen specificity of the transduced T(reg) lines was confirmed in vitro. T(reg) lines expressing the TcR with higher functional avidity showed stronger suppressive capacity in a linked suppression model in vitro. Furthermore, the same T(reg) lines demonstrated a stronger proliferation in vivo following antigen exposure. Pretreatment of recipient BL/6 mice with these T(reg) cells, together with anti-CD8 antibody and Rapamycin therapies, prolonged survival of BALB/c skins, as compared with mice that received T(reg) lines with lower TcR avidity. Taken together, these data suggest that the TcR functional avidity may be important for T(reg) function. It highlights the fact that strategies to select T(reg) with higher functional avidity might be beneficial for immunotherapy in transplantation.link_to_subscribed_fulltex