There is a growing body of evidence from non-human primate (NHP) studies to suggest that it will soon be possible to cure diabetes in humans by transplantation of pig islets. Although pig-to-NHP models based on the Edmonton protocol have provided the most compelling data (1,2), they also share its drawbacks: significant early loss of functional islet mass after infusion into the liver and the requirement for long-term immu-nosuppression to maintain graft function. It is clear that further advances will depend on reducing the immunosuppressive burden on the recipient, by providing greater protection to islet xenografts from innate and adaptive immunity. The three main approaches to this problem have been genetic modification of the donor pig, investigation of alternative transplant sites, and encapsulation. Proponents of encapsulation argue that coating islets with alginate-based polymers can immunoprotect xenografts to the extent that immunosuppression may no longer be necessary. This is supported by a number of rodent studies showing that microencapsulation promotes at least a prolongation of pig islet xenograft survival in untreated recipients (e.g., Ref. 3). Unfortunately, with the possible exception of a 1996 study (4) that is yet to be replicated, there has been no convincing demonstration that encapsulated pig islets reverse hyperglyce-mia in diabetic NHPs for longer than a few days or weeks. However, this may be about to change, with a report in this issue describing a promising new technique (5).
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