Mizoribine-An inosine monophosphate dehydrogenase inhibitor-acts synergistically with cyclosporine A in prolonging survival of murine islet cell and heart transplants across major histocompatibility barrier

Introduction: Mizoribine (MZR) is an inosine monophosphate dehydrogenase inhibitor. It has been widely used in Japan in the treatment of autoimmune diseases and is known to inhibit T and B cell proliferation. The aim of this study was to evaluate the efficacy of MZR as an immunosuppressive agent and determine its ability to synergize with a commonly used calcineurin inhibitor Cyclosporine A (CsA) in prolonging survival of murine islet cells and heart transplanted across major histocompatibility barrier. Methods: Murine allogeneic islet cell transplantation between Balb/c donor mice and C57BL/6 recipient mice and heterotopic heart transplantation was done between C3H/He donor mice and Balb/c recipient mice. Recipients were divided into groups based on immunosuppression: Group 1-No immunosuppression, Group 2-MZR alone (20. mg/kg/day), Group 3-CsA alone (20. mg/kg/day), Group 4-MZR + CsA (20. mg/kg/day). Donor specific IFN-γ, IL-10, IL-2, IL-4 secreting cells were enumerated by ELISpot. Serum cytokine and chemokine concentration was measured by Luminex. Results: Islet cell allograft recipients treated with CsA and MZR had prolonged islet function compared to other groups [normoglycemia (blood glucose < 200 mg/dL) up to 32 ± 4. days, p< 0.05]. Similarly, heart allograft survival was significantly improved in mice treated with CsA and MZR compared to other groups (50% 30-day survival, p= 0.04). Donor specific IFN-γ, IL-4, IL-2 secreting cells were significantly decreased in recipients treated with CsA and MZR with marked increase in IL-10 secreting cells (p< 0.05). There was also an increase in serum IL-10 with decrease in IFN-γ, IL-4, IL-2, MCP-1, and IL-6 in mice treated with CsA and MZR. Conclusion: MZR and CsA when used in combination are potent immunosuppressive agents in murine islet cell and heart transplantation models. These agents lead to a decrease in donor specific IFN-γ with increase in IL-10 secreting cells leading to improved allograft survival and function.