Studies of Innate and Adaptive Immunity in Islet Transplantation

Abstract: Clinical islet transplantation is today an established alternative treatment for a selected group of type 1 diabetes patients. The predominant technique for transplantation is infusion of islets in the liver via the portal vein. Obstacles to advancing islet transplantation include limited engraftment resulting from an immediate blood-mediated inflammatory reaction (IBMIR), a life-long need for immunosuppression and the shortage of organs available.In this thesis, innate and adaptive immunity were explored in allogeneic and xenogeneic settings, with the long-term goal of preventing islet graft destruction. Methods for studying immune responses to islets in blood and engrafted islets in liver tissue (intragraft gene expression) were developed and refined. The innate response to human islets and exocrine tissue in ABO-compatible blood was characterized up to 48 h using a novel whole-blood model. Physiological changes in the blood during incubations were explored and adjusted to allow prolonged experiments. Increased production of chemokines targeting CXCR1/2, CCR2 and CXCR3 was observed, accompanied by massive intra-islet neutrophil infiltration. Notably, endocrine and exocrine tissue triggered a similarly strong innate immune response.Two studies of adult porcine islet transplantation to non-human primates (NHPs) were performed. Expression of immune response genes induced in liver tissue of non-immunosuppressed NHPs (≤72 h) was evaluated after porcine islet transplantation. Up-regulation of CXCR3 mRNA, together with IP-10, Mig, MIP-1α, RANTES, MCP-1 and cytotoxic effector molecule transcripts, was associated with T-cell and macrophage infiltration at 48-72 h. Long-term survival (>100 days) of adult porcine islets in a NHP model was later demonstrated using T-cell-based immunosuppression, including co-stimulatory blockade (anti-CD154 mAb). Graft failure was associated with increased levels of circulating, indirectly activated T cells, non-Gal pig-specific IgG and gene transcripts of inflammatory cytokines. Microarray analysis of the response to inflammatory cytokines in cultured porcine islets identified genes involved in cell death, immune responses and oxidative stress; this gene pattern coincided with physiological changes (decrease in insulin and ATP content).In summary, allogeneic whole-blood experiments and xenogeneic in vivo studies underscored the importance of preventing early inflammation and cell-recruitment to avoid islet graft loss in islet transplantation. Long-term survival of porcine islets in NHPs was shown to be feasible using T-cell-directed immunosuppression, including anti-CD154 mAb.