Encapsulated islet transplantation: From allogeneic to xenogeneic transplantation

Islet transplantation is considered an ultimate modality for patients with diabetes mellitus. After adoption of the Edmonton protocol in 2000, clinical islet transplantation has increased the duration of insulin independence up to 5 years post-transplant. However, two major challenges limit the broad clinical application of islet transplantation: a shortage of organ donors and the need for immunosuppression. Islet encapsulation, a method of encasing islets in a semipermeable matrix to provide a physical immune barrier, is one of the strategies for overcoming these limitations. Islet encapsulation blocks immune-regulating cells with high molecular weights, while still allowing oxygen, insulin, and nutrients with low molecular weights to pass through the barrier. Currently, a number of encapsulation methods are being investigated in preclinical and clinical trials, including macroencapsulation, microencapsulation, conformal coating, and nanoencapsulation. Because of the shortage of pancreas donors, a xenogeneic pancreas may be considered as an alternate source for islet transplantation. In this chapter, we review the basic concepts of islet encapsulation and islet transplantation from allogeneic and xenogeneic sources.