215.3: CD80/CD86-CD28 costimulatory block enhance the regulatory T cell function with specificity and prolong islet allograft acceptance

Introduction: Induced T cells with suppressive functions (iTS) were generated by co-culturing recipient and donor lymphocytes in the presence of anti-CD80 and anti-CD86 monoclonal antibody [1]. We induced tolerance in 7 out of 10 patients in living donor liver transplantation with iTS [2]. ITS have donor-specific immune suppression and are composed of some cell subsets including regulatory T cell (Treg). However, the role of iTS-Treg and the mechanism of how they acquire antigen-specific suppressive functions remain unclear. In this study, we analyzed the effects of CD80/CD86-CD28 blockade on the function of iTS-Treg using a mouse islet transplantation model. Method: The alloantigen specific Treg were enriched from C57BL/6 splenocytes by coculturing with irradiated BALB/c splenocytes in the presence of antagonistic anti - CD80 and anti - CD86 monoclonal antibodies. ITS-Treg or naturally occurring Treg (nTreg) were co-transplanted with islet allografts under the kidney capsule of streptozotocin-induced diabetic recipient mice. The graft survival was monitored by blood glucose level. The suppressive function and the specificity of the Treg were investigated in mixed lymphocyte reaction. Results: ITS showed suppressive capacity in alloreactive immune responses. Co-transplantation with iTS-Treg under kidney capsule in islet transplantation significantly prolonged graft survival (iTS-Treg vs nTreg, P=0.016) (Figure 1). ITS-Treg significantly suppress alloreactive immune responses more than nTreg in vitro (iTS-Treg vs nTreg, P<0.01). CD80/CD86-CD28 blockade enhanced donor antigen-specific suppressive functions of iTS-Treg in vitro. Addition of IL-2 during generating iTS attenuated donor antigen-specific suppressive functions. Conclusion: ITS-Treg primed to donor antigens in the presence of low IL-2 induced by CD80/CD86-CD28 blockade enhanced donor antigen-specific suppressive function and prolonged islet allograft acceptance. References: 1. Hisashi B. Renal allograft rejection is prevented by adoptive transfer of anergic T cells in nonhuman primates. J.Clin. 2005; 115: 1896-1902. 2. Satoru T. A Pilot Study of Operational Tolerance With a Regulatory T-Cell-Based Cell Therapy in Living Donor Liver Transplantation. HEPATOLOGY. 2016; 64: 632-643.