Contact-dependent suppression pathways in non-human primate Tregs expanded ex vivo in the presence of Rapamycin (141.36)

Abstract

Abstract Regulatory T cell therapy offers a safe and effective alternative to achieve long-term graft survival by establishing a state of operational tolerance in the transplant recipient. Prior to use in human clinical trials, Treg therapy must be tested in non-human primate (NHP) pre-clinical models. To assess tolerogenic potential of Treg therapy, we used CD3/CD28 costimulation and frequent, low doses of IL-2 to expand natural CD4+CD25hi Tregs purified from NHP peripheral blood, with and without rapamycin. We achieved 500-800 fold expansion in 21 days and maintained high levels of CD25 and Foxp3.The ex vivo expanded Tregs were capable of inhibiting CD4 proliferation to anti-CD3 and allostimulation by 90%. Preliminary analyses of potential regulatory mechanisms employed by ex vivo expanded Tregs show high expression of CTLA4 and Granzyme B but little or no expression of TGF-b and IL-10 suggesting that these Tregs may function primarily through contact-dependent pathway. To our knowledge this is the first report of potential suppressive pathways used by ex vivo expanded NHP Tregs. Further investigations into suppressive molecules used by freshly isolated Tregs and whether ex vivo expansion selectively induced CTLA4 and Granzyme B are underway. These data establish the feasibility of using ex vivo expanded Tregs as part of a tolerogenic protocol in NHP model of islet transplantation.