Project 1: Augmenting Regulatory Mechanisms in Protocols of Transient Mixed Chimerism

PROJECT SUMMARY / ABSTRACT Induction of immune tolerance is the ultimate goal in the field of organ transplantation. Achieving a state of tolerance would lead to indefinite graft survival without chronic immunosuppression and its associated morbidity/mortality and is expected to prevent/reduce of chronic rejection. Tolerance of kidney allografts has been achieved in non-human primates (NHPs) and in humans by using a combination of nonmyeloablative conditioning and donor bone marrow transplantation that results in transient mixed hematopoietic chimerism. However, identical mixed chimerism protocols have failed to induce tolerance in NHP heart allograft recipients. This reflects the fact that there are organ-specific differences in tolerance induction with kidney (and liver) allografts being “tolerance-prone” and heart (and lung) grafts being “tolerance-resistant.” Despite the immune barriers posed by heart allografts, our laboratory has recently developed a novel protocol that has, for the first time, achieved long-term, stable tolerance of fully MHC mismatched heart allografts in cynomolgus monkeys. This remarkable result was attained in heart recipients by combining a transient mixed chimerism protocol with donor kidney cotransplantation which enhanced the contributions of host regulatory T cells (Tregs). Based on our preliminary data, we hypothesize that promoting the contributions of regulatory T cells and/or macrophages in recipients undergoing a transient mixed chimerism regimen will induce long-term and stable tolerance of heart allografts transplanted alone. We will test this hypothesis by 1) augmenting early host regulatory mechanisms using ex vivo expanded donor-specific MHC-reactive CAR Tregs in lieu of donor kidneys, 2) enhancing the function and stability of conventional host Tregs and infused CAR Tregs by targeting the DEPTOR and IL-2 pathways, and 3) using next-generation mTORi-specific nanotherapy to mitigate early innate inflammation and promote regulatory macrophages. These studies will be complemented by Project 2, which will test the corollary hypothesis that the development of conditioning regimens capable of inducing durable mixed chimerism will induce robust tolerance in heart recipients, and Project 3, that will investigate a novel costimulation blockade strategy to promote Tregs while constraining memory T cells after mixed chimerism conditioning. By elucidating and differentiating cellular and molecular mechanisms underlying effective versus ineffective protocols, Core A will inform and refine the treatment strategies proposed in each Project. We anticipate that together, these highly interactive projects will generate one or more safe and effective mixed chimerism tolerance protocols that will be ready for clinical trial in heart allograft recipients by the end of the funding period.