Marginal Transplantation Dose Study for the Treatment of Insulin-independent Type 1 Diabetes After Allogeneic Islet Transplantation in Macaca Fascicularis Monkeys

Abstract Many groups are working to improve the results of clinical allogeneic islet transplantation in a primate model. However, few studies have focused on the optimal islet dose for achieving normal glycemia without exogenous insulin after transplantation in primate models or on the relationship between rejection and islet amyloid polypeptide (IAPP) expression. We evaluated the dose (group 1/10,000, group 2/20,000, and group 3/>25,000 islet equivalents (IEQ)/kg) needed to achieve normal glycemia without exogenous insulin after transplantation using eleven cynomolgus monkeys, and we analyzed the characteristics exhibited in the islets after transplantation. Group 1 (n2) failed to control blood glucose level, despite injection with the highest dose of exogenous insulin, and group 2 (n5) achieved unstable control, with a high insulin requirement. However, group 3 (n4) achieved normal glycemia without exogenous insulin and maintained it for more than 60 days. Immunohistochemistry results from staining islets found in liver biopsies indicated that as the number of transplanted islets decreased, the amount of IAPP accumulation within the islets increased, which accelerated immune cell infiltration. In conclusion, the marginal transplantation dose for achieving a normal glycemia without exogenous insulin in our cynomolgus monkey model was >25,000 IEQ/kg, and the accumulation of IAPP early after transplantation, which depends on the transplanted islet dose, can be considered one factor in rejection.