IMPACT OF MICROGRAVITY CULTURE ON SURVIVAL OF ALLOGENEIC MOUSE PANCREATIC ISLET TRANSPLANTS

Abstract

P684 Aims: Diabetes mellitus (Type 1) remains a major cause of morbidity and mortality despite significant advances in medical management. Clinical pancreatic islet allotransplantation is a low-risk alternative to whole pancreas transplantation, offering great promise in treating patients. Although an Edmonton therapeutic protocol has dramatically improved the survival of islet allografts, the majority of patients eventually develop impaired graft function and chronic rejection. Therefore, the ultimate goal—to radically improve islet graft survival—is to induce transplantation tolerance. Methods/Results: We have developed a unique mouse model of tolerance to pancreatic islet allografts [C57BL10 (H2b) to C3H (H2k)] by culturing islets in microgravity conditions using rotating bioreactors. Islets cultured in bioreactors for 7 days displayed decreased immunogenicity (lack of dendritic cells), resulting in long-term allograft survival (>100 days; n = 18) with superior islet morphology and function. Indeed, transmission electron microscopy showed gradual loss of dendritic cells and scanning electron microscopy revealed development of multiple nutritional channels in islets cultured in the bioreactor. Similar results were obtained in C57BL10 to Balb/c (H2d) donor/recipient combination. However, although a 7-day culture produced long-term survival (>100 days; n = 4; p = 0.001), a limited 3-day culture shortened the survival to a mean survival time (MST) of 21.6 ± 5.8 days (n = 5; p = 0.026); fresh allogeneic islets survived 13.8 ± 2.7 days (n = 5). Interestingly, the results were different in Stat6 or Stat4 knockout (KO) mice deficient for Th2 and Th1 cells, respectively. Diabetic Stat6 KO mice rejected fresh islet allografts at 12.1 ± 1.6 days (n = 8) and Stat4 KO mice at 13.3 ± 2.4 days. Islets cultured for 3 days in the bioreactor achieved long-term survivals in all Stat4 KO recipients (>100 days; n = 7; p = 0.001). In contrast, Stat6 KO recipients transplanted with 3-day bioreactor islets produced a mixed response with some long-term survivals (>100 days; n = 4; p=0.001) and some rejectors (22.0 ± 1.7 days; n = 3; p = 0.01. Conclusions: Microgravity condition decreases immunogenicity of allogeneic islets. Furthermore, bioreactor-cultured islets induce stable long-term allograft survival by induction of IL-4/Stat6-dependent Th2reg cells.