Background: Pancreatic islet transplantation represents an innovative and effective therapeutic strategy to restore physiologic glycemic control for patients with T1DM who suffer from life-threatening hypoglycemia unawareness. However, several limiting factors prevent islet transplantation from replacing exogenous insulin therapy, including the shortage of matched organ donors and lifelong immunosuppression. Islet encapsulation strategies have the potential to reduce the adaptive immune response. We hypothesize that conformal islet coating with poly(N-vinylpyrrolidone) (PVPON) and tannic acid (TA) (PVPON/TA) will enhance human islet xenografts as well as murine islet allografts survival and function.

Methods: Human and murine pancreatic islets were conformally coated by utilizing non-toxic, non-ionic, and biocompatible PVPON and TA, to form 3.5 bilayer deposits. Confirmation that PVPON/TA does not hinder islet function was examined by the in vitro function of coated and non-coated human islets. The in vitro functionality of the coated and control islets was examined by measuring the insulin release in the presence of low and high glucose, islet oxygen consumption rates, and islet membrane integrity. In vivo function was evaluated by transplanting these human islets (1500IEQ) into diabetic immunodeficient Rag-/- mice. Subsequently, the immunoprotective properties of PVPON/TA coating were assessed by transplanting coated and non-coated islets in our well-established murine islet allograft model. BALB/c (H2d) mice served as islet donors while STZ-induced diabetic C57BL/6 (H2b) mice served as islet recipients.

Results: Both control and coated islets exhibited similar results in all in vitro assays performed (P>0.05). Human islet recipients transplanted with PVPON/TA coated islets reversed diabetes (n=4), proving this coating technique is non-toxic. Data from allograft recipients demonstrate that PVPON/TA coating as a monotherapy as well as an adjuvant to systemic immunosuppression reduces intragraft inflammation and delays allograft rejection.

Conclusions: The present study demonstrates that PVPON/TA coated islets retain their in vitro and in vivo functional potency. This transplant approach has the potential to reduce post-transplant inflammatory responses, high possibility of translation to clinical investigation, improve islet allograft survival and function, and eliminate the need for toxic, systemic immunosuppression. Ultimately this approach has the potential to increase the prevalence of single human pancreatic donor success, lead to long-term durable graft function, and broaden the spectrum of T1D patients eligible to receive curative ß-cell replacement therapies.