Preparation of Immunotolerant Space Under the Skin and Transplantation of Islets in the Space

A method that realizes allogeneic islet transplantation into a subcutaneous site under no immunosuppressive treatment has been desired for the treatment of type 1 diabetes. In this study, two donor/recipient combinations were used: F344 rat donors (RT-1l(v1)) and ACI rat recipients (RT-1(a)); and Wistar rat donors (closed colony) and Lewis rat recipients (RT-1(l)). An agarose rod, which carried basic fibroblast growth factor (bFGF; 50 mu g/rod, agarose-bFGF rod), was implanted into each of the two dorsal subcutaneous sites of a streptozotocin-induced diabetic rat for 7 days, and the space was formed by removal of the rod. One thousand five hundred allogeneic islets were transplanted into each of the subcutaneous spaces. No immunosuppressive medication was given before or after islet transplantation. The immunological analyses of the granulomatous tissue formed by agarose-bFGF rod were carried out with flow cytometry and gene expression to get some information for mechanism of acceptance of allogeneic islets. Subcutaneous spaces surrounded with highly vascularized granulomatous tissue were formed by agarose-bFGF rod implantation for 7 days. All recipients demonstrated long-term normoglycemia (>100 days) in both donor/recipient combinations. The percentages of regulatory T (Treg) cells/CD4 cells in the granulomatous tissue increased by the implantation of agarose-bFGF rod and the percentages remained high after islet transplantation. In addition, expression levels of genes associated with chemotaxis and induction of Treg cells increased in the granulomatous tissue by the implantation of agarose-bFGF rod. The agarose-bFGF rod implantation is a useful method for preparation of an immunotolerant site for successful allogeneic islet transplantation without immunosuppressive medication, and Treg cells might play a pivotal role in graft acceptance. Impact Statement Although transplantation of islets of Langerhans has been accepted as a fundamental treatment for insulin-dependent diabetes mellitus (IDDM), several problems are still remaining in order that it becomes the standard medical treatment of IDDM patients. In this study, using diabetic rat models, a subcutaneous space surrounded with highly vascularized granulomatous tissue was formed by agarose-bFGF rod implantation. Allogeneic islets transplanted into the space could survive and release insulin for a long period under no immunosuppressive medication. In conjunction with sufficient supply of islets from iPS/ES cells, our method can make islet transplantation the standard medical treatment of IDDM patients.