Microencapsulated non-human primate (NHP) islet allografts and porcine islet xenografts in streptozotocin-diabetic NHPs: islet survival, function, and host responses
Susan Safley1, Graham F Barber1, Dora Berman2, Robert Holdcraft3, Lawrence Gazda3, Camillo Ricordi2, Norma Kenyon2, Collin Weber1.
1Surgery, Emory University, Atlanta, GA, United States; 2Surgery, University of Miami, Miami, FL, United States; 3Xenia Division, Rogosin Institute, Xenia, OH, United States
Our goal is to develop approaches that enable long-term function of islet transplants as a cure for Type 1 diabetes. Our working hypothesis is that microencapsulation will enhance the function of both allogeneic and xenogeneic islets transplanted into the peritoneum in immunocompetent recipients. We have designed a durable, biocompatible two-layer alginate microcapsule that successfully excludes host IgG in both mouse and non-human primate (NHP) models.
Encapsulated islet allografts survived indefinitely in most diabetic NOD mice without immunosuppression. While microencapsulation alone or with dual costimulatory blockade (CTLA4-Ig and anti-CD154 mAb) did not promote indefinite survival of adult porcine islet (API) xenografts, immunoisolation plus immunosuppression synergistically resulted in long-term API survival (>150 days). The addition of a chemokine, CXCL12, to the alginate capsule prolonged API graft function for up to 616 days (433 ± 122 days, n=5) in diabetic NODs also given costimulatory blockade.
Two layer-encapsulated API xenografts were not as effective in streptozotocin-diabetic NHPs as in spontaneously diabetic NOD mice. Using dual costimulatory blockade, 3 NHPs received encapsulated API xenografts and 4 NHPs received encapsulated NHP islet allografts. Three of four allograft recipients also received the encapsulated islets with CXCL12. The allografts functioned longer than the xenografts (42, 59, 78, and 104 days versus 21, 28, and 70 days) as evidenced by more stable serum C-peptide levels and lower fasting blood glucose levels.
At necropsy, capsules were clean and free-floating in all 3 API xenograft recipients and in 3 of 4 allograft recipients. A host cellular reaction around the capsules was noted in one allograft recipient. Histologic analysis showed that encapsulated islets explanted at graft failure were fewer and smaller than the same encapsulated islets pre-transplant. Flow cytometric analysis of peritoneal cells demonstrated that host CD4+ T cells from all 7 NHPs were reduced compared to 3 non-transplanted controls, but host CD8+ T cells were at normal levels. The number of peritoneal macrophages was elevated in 2 of 3 islet xenograft recipients, compared to the allograft recipients and 3 normal control animals. In all 7 NHPs, levels of peritoneal cytokines were relatively low (<20 pg/mL), while certain chemokines (especially IP-10 and MCP-1) were strikingly higher than controls. Encapsulated API islet xenografts invoked higher levels of IL-6, IL-8, IP-10, and MCP-1 than encapsulated islet allografts. Genomics of explanted encapsulated APIs suggested that both immune and non-immune factors may have a role in the loss of islet function in NHP recipients. Our analysis of explanted capsules and islets suggests that both hypoxia and host immunoreactivity, but not fibrosis or capsule breakage, may be involved in graft failure.
11:00 - 13:30
|Prospects for Clinical Islet Xenotransplantation (CIX)||Commentary on Microencapsulated porcine islets - where to go from here by Shinichi Matsumoto||Room 109|
11:00 - 12:30
|Cellular Encapsulation||Microencapsulated non-human primate (NHP) islet allografts and porcine islet xenografts in streptozotocin-diabetic NHPs: islet survival, function, and host responses||Room 111-112|