224-OR: Effect of PD-L1 Overexpression on Autoreactive T-Cell Responses toward Stem Cell–Derived Beta Cells

Introduction & Objective: The recent successful large-scale generation of human stem cell (hPSC)-derived β-like cells (sBC) provides an abundant cell source for replacement therapy efforts to treat patients suffering from autoimmune diabetes. However, even in the presence of systemic immune suppression, transplanted sBC, like primary human islets, are susceptible to allogeneic and recurrent autoimmune attack. Different strategies leveraging genome engineering technologies have been tested to achieve localized immune protection for β-cell grafts. Increased expression of the immune checkpoint inhibitor PD-L1 at the graft site has shown promise in reducing either xenogeneic or allogeneic immune responses in preclinical animal models. However, whether PD-L1 expression can protect sBC grafts from recurring autoimmunity is poorly understood, largely due to the absence of appropriate model systems. Methods: Here we adoptively transferred diabetogenic mouse T cells from NOD mice expressing human HLA class I into immunodeficient NSG mice bearing HLA matched sBC grafts as a novel model of human autoimmunity in vivo. Results: Using this novel autoimmune in vivo model, sBC grafts that were genetically modified to express high levels of PD-L1 exhibit greater survival compared to unmodified control grafts but were also lost within 3 weeks due to robust T cell infiltration. Interestingly, we also observed destruction of HLA class 1 knockout sBC grafts, suggesting a potential and important role for autoreactive CD4+ T cells. We are currently expanding our findings using HLA matched in vitro co-culture assays and performing additional transplantation studies with purified diabetogenic CD8+ T cells. Conclusion: Collectively, our data suggest that PD-L1 expression on sBC alone might not provide sufficient protection from recurring autoimmunity, unlike allogenic responses, and highlights the need for better model systems to interrogate human autoimmunity in a matched manner.