This study was performed to observe the long-term effect of FTY720 on lymphocyte count change and islet allograft survival. Diabetic C57BL/6 mice were given FTY720 (group 1, 0.5 mg/kg/day; group 2, 1.0 mg/kg/day) or its vehicle (group 3, controls) after transplantation. Median graft survival time was prolonged in a dose-dependent manner (group 1, 84.5 days; group 2, >100 days, and group 3, 10 days, P < 0.01). Peripheral blood lymphocytes in groups 1 and 2 decreased to 23.81% and 12.59% compared with control group after FTY720 treatment. Lymphocytes from mesenteric lymph nodes and axillary nodes in groups 1 and 2 significantly increased on day 5, but decreased on day 14. Lymphocyte infiltration to the graft site was attenuated in groups 1 and 2. In conclusion, continuous FTY720 administration can induce and maintain lymphopenia, and inhibit lymphocytes from infiltrating the graft site so as to prolong islet allograft survival in mice.
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