INDUCTION OF HYPORESPONSIVENESS TO FULLY-MISMATCHED CARDIAC ALLOGRAFT AND GENERATION OF REGULATORY CELLS BY MCI-186 (FREE RADICAL SCAVENGER)

Abstract

P968 Aims: MCI-186 (3-methyl-1-phenyl-2-pyrazolin-5-one), a newly-developed free radical scavenger, has been recently shown to reduce reperfusion injury in isolated perfused heart or liver model in rat. In this study, we examined the ability of MCI-186 to induce prolonged survival of fully-mismatched cardiac allograft in mice. Methods: CBA mice (H2k) were given intravenous injection of 10mg/kg MCI-186 or control saline the same day as transplantation of a heart from C57BL/6 mice (H2b). To elucidate the mechanisms, an adoptive transfer study was conducted. From the mice with functioning allograft after treatment with MCI-186, 50 x 106 of splenocytes were adoptively transfered into naive CBA mice (secondary recipients) 30 days after cardiac transplantation. On the same day as adoptive transfer, the secondary recipients underwent cardiac transplantation. In vitro assay using mixed leukocyte culture (MLC) were also performed. Results: Naive CBA mice rejected C57BL/6 cardiac grafts acutely (median survival time [MST], 9 days). Control mice treated with saline also rejected the allografts acutely (MST, 8 days). Single dose of MCI-186 induced significant increase in graft survival (MST, 87.5 days). Histological examination showed that allograft treated with MCI-186 had preserved structure with few leukocyte infiltration 30 days after transplantation, compared to that in control saline group. In adoptive transfer study, all of the allografts enjoyed prolonged survival over 40 days in the secondary recipients with adoptive transfer from the CBA recipients treated with MCI-186. On the other hand, the control secondary recipients with adoptive transfer of naive CBA splenocytes rejected allografts acutely (MST, 14 days). These data suggest that regulatory cells were generated in the recipient treated with single dose of MCI-186. In MLC assay, addition of MCI-186 to MLC did not suppress cellular proliferation on alloimmune response. However, responder cells from the recipients treated with MCI-186 showed decreased proliferation compared to that from the recipients without treatment. These data suggest the ablity of MCI-186 to protect allograft in vivo without direct effect of proliferative hyporesponsiveness in MLC. Conclusions: Single dose of MCI-186 on the same day of transplantation induced significant prolongation of cardiac allograft survival and generated regulatory cells.