Development and application of a non-rejectable islet graft using indoleamine 2,3-dioxygenase (IDO) in diabetes.

Type 1 diabetes (T1D) is a devastating disease affecting more than 22 million people worldwide. Early diagnosis and treatment of T1D requires a deep understanding of the mechanisms underlying the progression of autoimmune diabetes. It has been shown that impaired IFNγ-induced indoleamine 2,3-dioxygenase (IDO) expression in dendritic cells of early prediabetic female nonobese diabetic (NOD) mice could contribute to their defective self-tolerance. IDO is an immunomodulatory and rate-limiting enzyme in tryptophan catabolism. Since fibroblasts are important components of islet extracellular matrix (ECM), we investigated IFNγ-induced IDO expression in NOD dermal fibroblasts. Our findings indicate that IFNγ fails to induce IDO expression in NOD dermal fibroblasts and moreover that the mechanism underlying this defect involves defective STAT1 phosphorylation in the IFNγ-induced-IDO signaling pathway. We further showed that an IFNγ-independent IDO expression pathway is operative in NOD mice fibroblasts. Islet transplantation, a promising strategy to restore efficient insulin regulation in T1D, is limited by poor post-transplant islet survival and toxicity of immunosuppressants. We developed a novel bioengineered cross-linked collagen matrix (CCM) to act as an ECM for the islets and found that islet function and survival significantly improved with this scaffold. We previously showed that in an IDO-mediated microenvironment, infiltrated immune cells but not islet cells cannot survive or proliferate. Here, we used IDO to generate a local immunomodulated environment, in which transplanted islets could remain viable and protected without compromising systemic immunity. We developed an improved islet allograft composed of stable IDO-expressing dermal fibroblasts (by lentiviral transduction) and allogeneic islets embedded within CCM in streptozotocin-induced diabetic mice. This IDO-expressing matrix did not compromise islet function or survival. IDO expression significantly suppressed the proliferation of alloantigen-stimulated splenocytes. Finally, we showed that local IDO expression delivered by a lentiviral vector significantly prolonged islet allograft survival by increasing the population of FOXP3+ cells at the graft site and preventing T cell infiltration. Overall, the studies in this thesis showed how defects in the IDO signaling pathway may underlie autoimmune diabetes and highlighted the therapeutic potential of IDO expression and improved matrices for enhancing survival and function of islet transplants in T1D.Medicine, Faculty ofMedicine, Department ofExperimental Medicine, Division ofGraduat