Improvement of Subcutaneous Bioartificial Pancreas Vascularization and Function by Coencapsulation of Pig Islets and Mesenchymal Stem Cells in Primates

Insufficient oxygenation can limit the long-term survival of encapsulated islets in subcutaneous tissue. Transplantation of coencapsulated pig islets with adipose or bone marrow mesenchymal stem cells (AMSCs or BM-MSCs, respectively) was investigated with regard to implant vascularization, oxygenation, and diabetes correction in primates. The in vivo impact of MSCs on graft oxygenation and neovascularization was assessed in rats with streptozotocin (STZ)-induced diabetes that were subcutaneously transplanted with islets coencapsulated with AMSCs (n = 8) or BM-MSCs (n = 6). Results were compared to islets encapsulated alone (n = 8). STZ diabetic primates were subcutaneously transplanted with islets coencapsulated with BM-MSCs. (n = 4) or AMSCs (n = 6). Recipients were monitored metabolically and immunologically, and neoangiogenesis was assessed on explanted grafts. Results were compared with primates transplanted with islets encapsulated alone (n = 5). The cotransplantation of islets with BM-MSCs or AMSCs in diabetic rats showed significantly higher graft oxygenation than islets alone (3% and 3.6% O-2 for islets + BM-MSCs or AMSCs, respectively, vs. 2.2% for islets alone). A significantly better glycated hemoglobin correction (28 weeks posttransplantation) was found for primates transplanted with islets and MSCs (7.4% and 8.1%, respectively) in comparison to islets encapsulated alone (10.9%). Greater neoangiogenesis was found in the periphery of coencapsulated islets and AMSCs in comparison to islets alone (p < 0.01). In conclusion, the coencapsulation of pig islets with MSCs can improve significantly the islets' survival/function in vitro. The coencapsulation of islets with MSCs improves implant oxygenation and neoangiogenesis. However, the cotransplantation of islets with MSCs improves only slightly the long-term function of a subcutaneous bioartificial pancreas in a primate preclinical model.