Development and application of a non-rejectable composite pancreatic islet allograft using indoleamine 2, 3 dioxygenase in a diabetic mouse model

Success of transplantation of pancreatic islets as a promising therapeutic method for restoring efficient regulated insulin secretion in type 1 diabetes depends on lifelong use of immunosuppressive drugs. With the goal of eliminating the necessity of systemic immunosuppressive agents after islet transplantation, in this doctoral research project we hypothesized that a novel non-rejectable islet graft through employing a local immunosuppressive factor, indoleamine 2, 3 dioxygenase (IDO) can be developed and applied. IDO is a tryptophan degrading enzyme and functions as a potent immunomodulatory factor. To address this hypothesis, we engineered a three-dimensional composite islet graft equipped with IDO expressing bystander cells as local immunosuppressive system. In this composite graft, expression of IDO in syngeneic fibroblasts provided a low tryptophan microenvironment within which T-cells could not proliferate and infiltrate islets. Three specific aims were accomplished in this study. We first showed that local expression of IDO in syngeneic bystander fibroblasts efficiently suppressed in vitro proliferation of lymphocytes stimulated with allogeneic pancreatic islets. In the next phase, the impact of IDO on viability and function of mouse islets embedded within IDO-expressing fibroblast-populated collagen matrix was investigated. The result showed no reduction in islet cells viability and comparable insulin content and secretion in IDO-expressing versus control preparations. In contrast to lymphocytes, a nutrient deficiency stress-responsive pathway was not activated in islets co-cultured with IDO-expressing fibroblasts confirming the selective suppressive effect of IDO on immune versus islet cells. Furthermore, when allogeneic immune response was eliminated by using a syngeneic transplant model, IDO-expressing composite islet grafts were functional in vivo for up to 100 days. Finally, to address the last specific aim, composite allogeneic islet grafts were transplanted into renal subcapsular space of streptozotocin-induced diabetic immunocompetent mice. IDO-expressing grafts survived significantly longer than controls without using any systemic immunosuppressive agent (41.2±1.64 vs. 12.9±0.73 days, p