Formation of Composite Islet Grafts : A novel strategy to promote islet survival and revascularization

Sammanfattning: The islets of Langerhans are small and delicate spheroid organs scattered in the pancreas responsible for insulin production. Transplantation of isolated islets is a beneficial therapy for patients with a severe form of type 1 diabetes. The islets, which normally are richly vascularized in the pancreas, are completely disconnected from the vascular support by the enzymatic digestion during the isolation procedure. Islet viability is affected throughout all steps in this process, from donor death and isolation of islets to culturing and the transplantation process itself. In this thesis a novel strategy to promote islet survival and to re-establish islet vasculature is presented. We show endogenous expression of 51 different genes related to inflammation in cultured islets. Among these genes high expression of MCP-1, MIF, VEGF, thymosin b-10 and IL-8, IL-1β, IL-5R-a, IFN-γ antagonist were found in all donors during the 5- and the 2-day cultures, respectively. Protein expression of these genes can stimulate inflammatory immune responses but also promote tissue repair by attracting curative cells such as endothelial cells (EC) leading to re-establishment of the vasculature. We have established a novel technique by formation of composite islets using EC and mesenchymal stem cells (MSC). EC adhered on the surface of the islets and created a potential blood tolerant surface. The EC-islets showed a degree of protection from the detrimental effects of instant blood-mediated inflammatory reaction (IBMIR) with the major components of IBMIR being decreased in in vitro assays. We combined MSC to the EC-islets with success. The MSC were found to have proliferative effect on EC and the combination of these two cell types on the islets further increased the EC covered surface compared to EC-islets. The EC-MSC-islets in co-culture formed vessel-like structures both into the islets and out to the surrounding matrix. The MSC enhanced the exogenous EC to form vessel-like network in the EC-MSC-islets indicating vascular support by the MSC. The novel strategy and conditions presented herein could alleviate problems related to survival of the islets by promoting revascularization. This would open up a new era in islet transplantation and allow more patients to benefit from this therapy.