Abstract

Both CD4+ and CD8+ Tregs play a critical role in the control of immune responses and immune tolerance; however, our understanding of CD8+ Tregs is limited while they are particularly promising for therapeutic application. We report here existence of highly suppressive human CD8+CD45RClow/− Tregs expressing Foxp3 and producing IFNγ, IL-10, IL-34, and TGFβ to mediate their suppressive activity. We demonstrate that total CD8+CD45RClow/− Tregs can be efficiently expanded in the presence of anti-CD3/28 mAbs, high-dose IL-2 and IL-15 and that such expanded Tregs efficiently delay GVHD and human skin transplantation rejection in immune humanized mice. Robustly expanded CD8+ Tregs displayed a specific gene signature, upregulated cytokines and expansion in the presence of rapamycin greatly improved proliferation and suppression. We show that CD8+CD45RClow/− Tregs are equivalent to canonical CD4+CD25highCD127low/− Tregs for suppression of allogeneic immune responses in vitro. Altogether, our results open new perspectives to tolerogenic strategies in human solid organ transplantation and GVHD.

Highlights

  • Immunosuppressive regimens have significantly improved long-term graft survival in the last decades but they still cannot prevent the allograft from chronic graft dysfunction and they remain a significant obstacle for the welfare of transplanted patients, in the last years, improvement of allograft survival has stagnated [1]

  • As in the rat we previously demonstrated the preferential interaction of CD8+CD45RClow/− Tregs with Plasmacytoid dendritic cells (pDCs) for an optimal suppressive activity [39], we tested the suppressive potential of CD8+CD45RClow/− Tregs in the presence of conventional dendritic cells (cDCs) (CD3−CD19− CD1c+Nrp-1−) and pDCs (CD3−CD19−CD1c−Nrp-1+) sorted simultaneously, in comparison to total MHC class II+ APCs as stimulator cells (Figure 1D)

  • In a model of cardiac allotransplantation, we have observed that fresh CD8+CD45RClow/− Tregs expressed ~2% of Foxp3 [8] and that Foxp3 was not upregulated following activation [28], the absence of Foxp3-deficient rat models remains a limitation for characterization of the role of Foxp3 in this model of transplantation

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Summary

Introduction

Immunosuppressive regimens have significantly improved long-term graft survival in the last decades but they still cannot prevent the allograft from chronic graft dysfunction and they remain a significant obstacle for the welfare of transplanted patients, in the last years, improvement of allograft survival has stagnated [1]. Phase I studies in GVHD and solid organ transplantation have started with regulatory cells from different types (different CD4+ Tregs, macrophages, and DCs) without apparent toxicity [5,6,7], but to date, there are no clinical trials using CD8+ Tregs despite abundant literature in animals models [8,9,10]. Others have shown in mice that adoptive transfer of antigen-specific CD8+ Tregs were potent suppressors of fully MHC mismatch skin allograft and islet allograft [21, 22]. Our own studies have shown in a rat model of CD40-CD40L blockade-induced allograft tolerance the critical role of a CD8+ Tregs population expressing low/no level of CD45RC [8, 25]. Treatment with anti-CD45RC depleted CD45RChigh cells, preserved CD45RClow/− CD8+ and CD4+ Tregs and resulted in inhibition of solid organ rejection and of human GVHD in immune humanized mice [25]. We highlighted the biological role of IFNγ, IL-34, and Fibroleukin-2 (FGL-2) in the suppression exerted by CD8+CD45RClow/− Tregs [8, 17, 26,27,28]

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