The Study On The Mechanisms Of FTY720 And The Induction Of Transplantation Immune Tolerance With This New Immunosuppressant

Purpose: This study was designed to determine the potential of the pretreatment with FTY720 (FTY) to prolong cardiac allograft survival and explore its operational mechanism.Methods: Hearts of inbred BALB/c mice were transplanted heterotopically in C57BL/6 mice. Recipients were randomly divided into six groups. Group-1 was the nil-treated control. Group-2, Group-3 and Group-4 were given the monotherapy of FTY at the dose of 3mg/kg/d by oral gavage once a day. Time courses of administration in these three groups were different (Group-2:day-(-3) →day-11; Group-3:day-0→day-14; Group-4:day-(-3)→day-0). Group-5 were treated with Cyclosporine(CsA) (10mg/kg/d) and Group-6 were treated with RAD (3mg/kg/d) by daily oral gavage from day-(-3) to day-11. In Group-2, the peripheral lymphocytes number and T cell population were monitored. Long time survivors(>100d) in this group were detected with their IFN-γ and IL-4 levels and their tolerant state was challenged with second graft: skin from the same donor. In the in vitro study, mouse splenocytes were incubated with FTY, then the DNA was extracted and analyzed by gel electrophoresis. Also, the CD25 expression was observed by cytometry on T cells stimulated by Concanavalin A(ConA) in the present of FTY. Results: All grafts of FTY-treated groups had prolonged survival compared with the nil-controls (7-8 days, n=6). Whereas recipients of Group-3 rejected their allografts at a median survival time (MST) of 16.5 days (n=4), those in Group-2 showed significant prolongation of allograft survival (MST>55days, n=11) and 6 of them exceeded 100 days. The MST of Group-4 was 14 days(n=5) with one case exceeded 100days. In comparison, pretreatment of CsA or RAD had no such benefit. The MST of Group-5(n=5) and Group-6(n=5) were 10 days and 13 days respectively. In long term survivors of Group-2, the FTY-induced lymphopenia were found completely recovered when the drug had been withdrawn for six weeks, the level of IL-4 was up-regulated while that of IFN-γ was stable. The tolerant state induced by pretreatment of FTY was so robust that these long term survivors can accept the skin grafts from the same donors. In the intro study, the characteristic of apoptosis was showed by DNA fragmentatation in the mouse splenocytes incubated with FTY. FTY were also found to inhibit the expression of CD25 on T cells stimulated by ConA.Conclusion: We assumed tolerance to allograft was induced by and only by the pretreatment of FTY in this stuty. We postulate that pretreatment with FTY reduce the T cell population by apoptotic death, in the midest of death, the apoptotic cell actively inhibit the maturation of DC. In addition to these, FTY also down-regulate the CD25 on the T cell membrane. All these effects cooperate to induce the tolerance and maintain it by promoting regulatory machinery.