The usefulness of microencapsulation for pancreatic islet xenotransplantation without immunosuppression

The effectiveness of a newly developed microcapsule on islet xenotransplantation was examined in diabetic rat and canine recipients. The microcapsule is composed of 5% agarose, 5% polystyrene sulfonic acid, 1% polybrene and 1% carboxymethyl cellulose. These components play a role on immunoisolation, suppression of complement activity, and biocompatibility of the microcapsule. Hamster islets isolated by collagenase digestion method were encapsulated and implanted into the peritoneal space of streptozotocine-induced diabetic rat recipients. Encapsulated pig islets isolated by collagenase digestion and centrifugation on Ficoll discontinuous gradients were implanted into the peritoneal space of totally pancreatectomized diabetic canine recipients. The mean graft survival of 4 rat recipients with 3000 encapsulated hamster islets (124+/-44 days) was significantly longer than that of 5 rat recipients with naked 3000 islets (1+/-0 day), and their body weights increased significantly compared with those of untreated diabetic rats. Two of 5 canine recipients with encapsulated pig islets had 120 and 65 days of insulin free periods, when the body weight loss of the recipients was diminished. Porcine C-peptide levels in all live canine recipients with encapsulated islets elevated to 0.3 ng/ml, but was not detected in two recipients with naked islets. This microcapsule could prolong the xenoislet survival time in hamster to rat combination, and achieve insulin free time in pig to dog combination without immunosuppression. We believe this microcapsule could accomplish clinical use in future.