Introduction: Islet allografts are currently associated with a high rate of early insulin independence, but after 1 year insulin-independence rates rapidly decline for unclear reasons. In contrast, as shown here, islet autotransplants (IATs) show durable function and extended insulin-independence rates, despite a lower beta-cell mass.
Methods: IAT function was determined in 173 patients after total pancreatectomy at our center. Islet function was considered full in insulin-independent patients, partial when euglycemic on once-daily long-acting insulin (all tested were C-peptide positive), and failed if on a standard diabetic regimen. Outcomes for autoislet recipients by Kaplan-Meier survival analysis were compared with those of alloislet recipients in the Collaborative Islet Transplant Registry.
Results: IAT function (full/partial combined) and insulin independence correlated with islet yield. Overall only 65% functioned within the first year, and only 32% were insulin independent, but of IATs that functioned initially (n=112), 85% remained so 2-years later, in contrast to 66% of allografts (n=262). Of IAT recipients who became insulin independent (n=55), 74% remained so 2-years later versus 45% of initially insulin-independent allograft recipients (n=154). Of IATs that functioned or induced insulin independence, the rates at 5 years were 69% and 47%, respectively.
Conclusion: Islet function is more resilient in autografts than allografts. Indeed, the 5-year insulin-independence persistence rate for IATs is similar to the 2-year rate for allografts. Several factors unique to allocases are likely responsible for the differences, including donor brain death, longer cold ischemia time, diabetogenic immunosuppression, and auto- and alloimmunity. IAT outcomes provide a minimum theoretical standard to work toward in allotransplantation.