Alternative transplantation sites for pancreatic islet grafts

The liver is the current site of choice for pancreatic islet transplantation, even though it is far from being an ideal site because of immunologic, anatomic, and physiologic factors leading to a significant early graft loss. A huge amount of alternative sites have been used for islet transplantation in experimental animal models to provide improved engraftment and long-term survival minimizing surgical complications. The pancreas, gastric submucosa, genitourinary tract, muscle, omentum, bone marrow, kidney capsule, peritoneum, anterior eye chamber, testis, and thymus have been explored. Site-specific differences exist in term of islet engraftment, but few alternative sites have potential clinical translation and generally the evidence of a post-transplant islet function better than that reached after intraportal infusion is still lacking. This review discusses site-specific benefits and drawbacks taking into account immunologic, metabolic, and technical aspects to identify the ideal microenvironment for islet function and survival.