Prolonged euglycemia following intraperitoneal transplantation of encapsulated porcine islets.

Morgan Lamb^1,2,3, Michael Alexander^1,2,3, Rahul Krishnan^1,2,3, Tom Spizzo^1,2,3, Michael Martin^1,2,3, Remick Stahl^1,2,3, Jonathan RT Lakey^1,2,3

¹Surgery, University Of California Irvine, Orange , CA, United States; ²Biomedical Engineering, University of California Irvine, Orange, CA, United States; ³Spring point Project, Minneapolis, MN, United States

The limitations of current islet transplantation including the scarcity of organ donors, consistency of human islet isolations and the negative complications of chronic immunosuppression have stimulated researchers to explore both xenoislet transplantation and encapsulation to protect transplanted islets from the immune response. Our research group’s focus has been the development of a novel, robust, and scalable method of isolating and purifying piglet islets coupled with a stable alginate based microcapsule. The aim of this study was to demonstrate survival and function of these encapsulated porcine islets transplanted in diabetic immunocompromised and immmunocompetent mice. 

Six to eight-week old Athymic Nude (Nude) and C57BL/6 mice (n=20 per group,10M/10 F) were rendered diabetic with a single IV dose of streptozotocin (150 mg/kg). Diabetes was confirmed after 3 consecutive days of hyperglycemia and mice were maintained on insulin (Lantus, 1-2u/day SC) until islet transplantation. Control, non-transplanted mice (Nude and C57BL/6) were maintained on insulin for 28 days. Pancreatic tissue from pre-weaned Yorkshire piglets (22±0.4 days old) was cultured (37^oC/5%CO₂) after partial enzymatic digestion. After 7 days of culture, islets were then encapsulated in 3% alginate (capsule diameter 487±2.7um). Groups of diabetic mice were then transplanted with 3,000 encapsulated porcine islets into the peritoneal cavity. Mice were monitored daily for general health, 3 times a week for non-fasting blood glucose levels and weekly for body weight. Islets were evaluated post isolation and after explantation using islet enumeration (IEQ), viability (Newport green/PI) and function (GSIR,  Stimulation Index (SI)=insulin released in 28mM glucose over insulin released in 2.8mM glucose). No immunosuppression was administered to any mice.

Prior to transplantation, capillary non-fasting blood glucose in non-transplanted and control diabetic mice averaged 551.7±24mg/dL in Nude and 504.5±43 in C57BL/6 mice(mean±sem). All transplanted mice became euglycemic after islet transplantation. Average blood glucose levels were at 30 days (167.2±23mg/dL, Nude; 141±24mg/dL, C57BL/6), at 60 days (Nude 139.0±25mg/dL, Nude; 126±12mg/dL ,C57BL/6) and at 90 days (122.9±8 mg/dL, C57BL/6) post transplant.