Microencapsulation of rat islets prolongs xenograft survival in diabetic mice.

OBJECTIVE: To protect the transplanted islets from the host's immune system by means of immunoexclusion membranes. METHODS: Rat islets were isolated from Wistar rat pancreas by ductal collagenase distention, stationary digestion, and finally with the aid of dextran gradient separation. Then the islets were encapsulated in alginate-polylysine-alginate (APA) semipermeable membranes. RESULTS: In vitro studies demonstrated that encapsulated islets secreted insulin in response to glucose challenge for at least 8 weeks, which was similar to free islets. In vivo studies showed that 15 streptozotocin (STZ)-induced diabetic mice were transplanted intraperitoneally with 1000 encapsulated islets without immunosuppression. Diabetes was reversed within 3 days, and the mice remained normoglycemic for up to 160 days, with a mean xenograft survival time of 126 days. The encapsulated islets had a significantly greater effect than unencapsulated islets, which functioned for less than 8 days. CONCLUSIONS: Encapsulation of pancreatic islets in semipermeable membranes can effectively prolong xenograft survival without immunosuppression in an animal model.