Our long-range objective is to develop a CNI-free therapeutic approach to safely promote organ transplant tolerance. Two promising complementary but interactive approaches to regulatory immune cell therapy for transplant tolerance,- DCreg and Treg, comprise this U19 application. They will share a novel IS drug regimen, rationally-designed to enhance the regulatory function of these cells in graft recipients. In Project 1, our preliminary data show that donor-derived DCreg infusion before transplantation promotes renal allograft survival in rhesus macaques receiving a short-term, minimal IS regimen of costimulation blockade (CoSB) and tapered rapamycin. This effect is associated with selective attenuation of donor-reactive memory T cell (Tmem) responses. Recent clinical data show that lymphodepletion followed by CoSB and rapamycin maintenance prevents CoSB-resistant acute rejection and selectively inhibits recovery of donor-reactive Tmem, although operational tolerance was not achieved. We therefore hypothesize that a regimen comprising ATG, CoSB and rapamycin that (i) is more permissive to extended graft survival and that (ii) incorporates the immunomodulatory function of adoptively-transferred DCreg, will promote IS-drug free, donor-specific tolerance. In Project 2, we will address shortcomings of Treg therapy (Treg timing, specificity, instability or conversion to Teff) recently underscored in a recent NHP study by our group. We will do so by building on our success in expanding highly-suppressive, donor-alloreactive rhesus Treg (arTreg) ex vivo, and on the basis of our recent finding that IL-2 + TGFβ1/Fc can selectively promote rhesus Treg, while inhibiting Th17 responses. We hypothesize that delayed arTreg administration to ATG, CoSB and rapamycin-treated transplant recipients, together with low-dose IL-2 and TGFβ1/Fc, will enhance their stability/persistence, promote their suppressive function, overcome Tmem activity and promote transplant tolerance. Our Overall Aims are: Project 1: To determine the capacity of DCreg infusion to promote operational renal transplant tolerance in NHP given combined ATG (lymphodepletion) and CoSB (belatacept or αCD40 mAb) plus rapamycin maintenance. Project 2: To determine the capacity of alloreactive Treg to promote operational renal transplant tolerance in NHP given combined ATG, CoSB (belatacept) plus rapamycin maintenance, together with low-dose IL-2 ± huTGFβ1Fc. Both projects will be accompanied by highly-interactive, mechanistic studies and assess novel biomarker (eomesodermin) expression by alloreactive Tmem as a potential predictor of transplant outcome/tolerance. They will be supported by an Administrative and Biostatistics Core (Core A) and a Transplant Pathology and Tissue Imaging Core (Core B), and utilize agents from the NIAID NHP Reagent Resource.