Combination therapy of an iNKT cell ligand and CD40–CD154 blockade establishes islet allograft acceptance in nonmyeloablative bone marrow transplant recipients

Aims Islet transplantation is an effective therapeutic option for type 1 diabetes. Although maintenance immunosuppression therapy is required to prevent allogeneic rejection and recurrence of autoimmunity, long-term allograft survival has not yet been achieved partly because of its adverse effects. The induction of donor-specific immunotolerance is a promising approach for long-term allograft survival without maintenance immunosuppression therapy. We previously reported that combination therapy using a liposomal ligand for invariant natural killer T cells, RGI-2001, and anti-CD154 antibody established mixed hematopoietic chimerism for the induction of donor-specific immunotolerance. This study investigated whether the protocol could promote islet allograft acceptance in experimental diabetes. Methods Streptozotocin-induced diabetic BALB/c mice were transplanted with bone marrow cells from C57BL/6 donors and received combination therapy of RGI-2001 and anti-CD154 antibody after 3-Gy total body irradiation. 3 Weeks after bone marrow transplantation, islets isolated from C57BL/6 donors were transplanted under the kidney capsule. Results Mixed chimerism was established in diabetic mice receiving the tolerance induction protocol. After islet transplantation, blood glucose levels improved and normoglycemia persisted for over 100 days. Hyperglycemia recurred after islet grafts were removed. Histopathological examinations showed insulin-positive staining and absence of cellular infiltration in the islet grafts. T cells of recipients showed donor-specific hyporesponsiveness, and anti-donor antibodies were not detected. Conclusions The tolerance induction protocol with combination therapy of RGI-2001 and anti-CD154 antibody promoted islet allograft acceptance in a mouse diabetic model. This protocol may be clinically applied to islet transplantation for type 1 diabetes mellitus.