This study examined the effect of long-term administration of low-dose FTY720 on survival of murine cardiac allograft and the possible mechanism.Murine models of abdominal heterotopic heart transplantation were established.Low-dose FTY720 (0.3 mg/kg) was administrated to the animals 4 days before the transplantation of cardiac allografis until the occurrence of rejection or the observation terminals.The animals without FTY720 treatment and those with syngencic cardiac grafts transplanted served as controls.The mean survival time (MST) of grafts,and T lymphocyte subsets in gratis,peripheral blood and lymphoid organs were measured by histopathological examination or flow cytometry,and compared among groups.The results showed that the MST of allografts in FTY720-treated mice was more than 40 days,significantly longer than that in the untreated group (MST=8 days,P＜0.01).After the long-term administration of FTY720,the proportion of CD4+ and CD8+ lymphocytes in peripheral blood was diminished significantly,but the proportion ofCD4+ lymphocytes was increased in mesenteric lymph nodes (MLNs) and spleen.lmmunofluorescence staining revealcd that the infiltration of CD4+ and CD8+ lymphocytes in allografts was significantly inhibited after long-term administration of low-dose FTY720.It was concluded that low-dose long-term administration of FTY720 could promote T lymphocytes in lymphatic organs and decrease their infiltration in allografts,resulting in the inhibition of rejection and the long-term survival of allografts.