Development and Implementation of Immunomodulatory Methods to Prolong Transplant Survival


Transplantation is necessary and often the only viable treatment for many forms of end stage organ failure. While advances in immunosuppressive therapies have facilitated largely blocking acute rejection, 5-10 year post-transplant attrition rates have not significantly improved in the past 30 years. The predominant antigen facilitating the alloimmune response is the donor major histocompatibility complex. In this thesis, I construct and assess immunosuppression free methods to prolong transplant survival in the clinical contexts of transplant tolerance induction, cytomegalovirus reactivation, and cardiac allograft vasculopathy (CAV). In the first section, I designed, characterized, and tested the ability of differently engineered formulations of donor antigen specific poly(lactic-co-glycolic) acid (PLG) nanoparticles (NP) to induce tolerance in a murine skin transplant model. NP formulations were compared to a donor-specific tolerance treatment, 1-ethyl-3-(3’-dimethyl-aminopropyl)-carbodiimide-treated splenocytes (ECDI-SP). I determined that NPs conjugated to a short donor peptide could significantly increase allograft survival, but could not reproduce ECDI-SP mediated permanent tolerance due to increased graft cytotoxic T cell infiltration, APC cytokine production, and differential splenic phagocyte biodistribution. Secondly, I evaluated the true tolerance of ECDI-SP by performing islet transplants at the time of treatment and later implanting same donor uninfected or murine cytomegalovirus (MCMV) latently infected kidneys. Using MCMV grafts, I addressed whether ischemia/reperfusion injury is sufficient to reactivate virus in pre-tolerized recipients and if ECDI-SP afforded anti-viral protection. ECDI-SP continued donor islet protection after kidney implantation and protected uninfected kidney transplants, but latently infected kidney second transplants reactivated virus, disseminated viral DNA, and elevated graft inflammation. The final focus of the thesis is on the role of macrophage cell-surface phagocytosis receptor MerTK in CAV. CAV shares similarities with atherosclerosis, the latter where MerTK has demonstrated reduction of vascular inflammation and disease progression. Additionally, MerTK is a critical receptor in ECDI-SP mediated tolerance. Using murine heterotopic heart transplant models, I determined that MerTK genetic deficiency accelerated CAV, while genetically-stabilized MerTK (MertkCR) prolonged allograft survival. In vitro co-culture experiments identified a new pathway where activated CD8+ T cells promote the shedding of solubilized MER from macrophages, leading to impaired function and increased macrophage inflammation. Currently, immunosuppression requires life-long compliance and is associated with numerous side effects Overall, this work furthers the understanding of potential therapies and targets that can be leveraged to safely extend allograft survival.

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