ABSTRACT: Renal transplantation represents first-line therapy for patients with end-stage renal disease, with the most recent data documenting high one-year success rates. However, patients continue to face significant morbidity and mortality after transplant, both from chronic allograft rejection and from the toxicities associated with standard immunosuppressive regimens. Given these dual risks, the ultimate goal in this field is the induction of immune tolerance after transplantation, which promises life-long acceptance of an allograft, without the need for ongoing immunosuppression and importantly, with preservation of protective immunity. While novel pharmacologic and antibody-based therapies represent real promise in terms of prolonging allograft survival and reducing off-target toxicities, murine studies strongly suggest that the most robust strategies for inducing immune tolerance incorporate cellular therapies, including both regulatory T cell-based approaches and mixed- chimerism induction (especially in combination with T cell costimulation blockade). Both of these therapies hold the promise of fundamentally resetting recipient immunity in favor of allograft acceptance, and thus providing a direct pathway towards immune tolerance for renal transplant recipients. In this proposal, we will investigate the tolerance-induction potential of both Treg- and Mixed-Chimerism-based cellular therapies through the following Aims: Aim 1: To engineer an optimally suppressive regulatory T cell product, able to provide allograft-specific immune tolerance after renal transplantation. Aim 2: To induce immune tolerance to a renal allograft through the induction of stable, multilineage mixed-hematopoietic chimerism with preservation of protective immunity in the setting of T cell costimulation blockade. The deliverables for this Project include the development of two highly promising tolerance-induction strategies for clinical translation, which, if successful, could change clinical practice in renal transplantation.