Current Assessment of Clinical Pancreatic Islet Allotransplantation

Clinical islet allotransplantation represents a minimally invasive, efficacious alternative to pancreas transplantation for restoring glycemic control and insulin independence in select patients with type 1 diabetes that is complicated by intractable impaired hypoglycemia awareness and/or severe hypoglycemic events refractory to stabilization by other means. Over the last decade, islet transplantation outcomes have steadily improved in part due to refinements in the selection of optimal donors, islet isolation techniques, safer engraftment methods, and effective immunomodulatory and anti-inflammatory therapies. Insulin independence rates at five years post-transplantation at select centers have reached parity with pancreas alone transplantation, and marked progress has been achieved in islet transplantation outcomes using single-donor pancreas. However, widespread application of the procedure is still hindered due to a limited supply of donor pancreases, inadequate engraftment, and the harmful side effects of chronic immunosuppression. Strategies to address some of these challenges involve the use of alternative sources of beta cells or islets, extrahepatic sites of implantation, encapsulation of islets and novel therapies to induce tolerance. While several countries have now transitioned islet transplantation from experimental status to a funded clinical cure for patients with brittle type 1 diabetes that cannot be stabilized by more conventional means, in the US it still awaits regulatory approval and a financial mechanism for sustainable reimbursement. This review details the history and the current status of clinical islet allotransplantation while summarizing improvements that have been made in techniques involving isolation, purification, culture and assessment of human islets as well as the islet transplantation process itself. Furthermore, it discusses the limitations encountered that prevent its widespread application, strategies that address those limitations, and last but not least, clinical trials being conducted that will help position islet transplantation as a mainstay treatment for the cure of type 1 diabetes.