Composite Islet‐Endothelial Cell Grafts: A Novel Approach to Counteract Innate Immunity in Islet Transplantation

Abstract

An instant blood-mediated inflammatory reaction (IB-MIR) is elicited when islets come in contact with blood after intraportal transplantation. In contrast, endothelial cells (EC) readily tolerate contact with blood. A conceivable strategy to overcome IBMIR would be to create composite islet-EC grafts. Human islets were cocultured with primary human aortic endothelial cells (HAEC) for 2-7 days to obtain 50-90% coverage. HAECcoated islets were exposed to ABO-identical blood and analyzed with regard to clotting time, signs of inflammation and cell infiltration. Composite islet-HAEC graft survival was assessed after transplantation to athymic (nu/nu) nude mice. Exposed to blood, HAECcoated islets induced less activation of coagulation and complement compared to control islets. Also, platelet and leukocyte consumption in blood was decreased. Clots with entrapped HAEC-coated islets showed less infiltration of CD11b+ cells. The extent of protection correlated to the level of HAEC coverage. Transplanted composite grafts stained positive for insulin and PECAM-1 demonstrating presence of both islets and HAEC within the islet graft 7 weeks after transplantation. Composite islet-HAEC grafts reduce all components of IBMIR. Refinement of the technique will allow introduction of composite islet-EC grafts in clinical islet transplantation, using autologous EC expanded in vitro and kept frozen until allogeneic islets become available for that specific recipient. Key words: Endothelial cells, human, islets of LangerhansAbbreviations: AEC, 3-amino, 9-ethyl-carbazole; C3a, Complement3a; CD, cluster of diffrentiation; EC, endothelial cells; ELISA, enzyme-linked immunosorbent assay; HAEC, human aortic endothelial cells; IBMIR, instant blood-mediated inflammatory reaction; IDDM, insulin-dependent diabetes mellitus; IEQ, islet equivalents; PBS, phosphate-buffered saline; PVC, polyvinyl chloride; SEM, scanning electron microscopy; SEM, standard error of the mean; TAT, thrombin anti-thrombin; VEGF, vascular endothelial growth factor.

Anchoring of Vascular Endothelial Growth Factor to Surface-Immobilized Heparin on Pancreatic Islets: Implications for Stimulating Islet Angiogenesis

“…Our group has previously established an approach for improving islet revascularization by coating islets with ECs. 40,41 In this study, we questioned whether the EC coating efficiency could be affected by VEGF-A anchored to the surface of heparinized islets. Confocal microscopy of the islets revealed significant increased adhesion of ECs to the surface of heparinized islets, an effect that was further improved when heparinized islets were preincubated with VEGF-A.…”

Formation of Composite Endothelial Cell–Mesenchymal Stem Cell Islets

“…The same relationship, possibly reflecting variations in integrin expression (25), seems to hold true for their ability to coat islet surfaces (cf. [7]). …”

Optimising islet engraftment is critical for successful clinical islet transplantation

“…If anything, the small size of the islets would facilitate their engraftment. The intramuscular site would also allow transplantation of composite isletendothelial cell grafts [46,48] or the application of various matrices carrying growth factors that would facilitate the formation of a new endocrine organ at the new site of implantation. Indeed, in autotransplants, we have successfully transplanted isolated islets of Langerhans intramuscularly into the forearm of a patient undergoing total pancreatectomy because of recurrent life-threatening pancreatitis [49].…”