A Combination of Donor Specific Transfusion and Rapamycin Prolonges Cardiac Allograft Survival in Mice

Background. We sought to investigate the effects of donor-specific transfusion (DST) combined with rapamycin (RPM) on engraftment and demonstrate the mechanisms. Methods. B6 was treated with DST (on day -8) combined with RPM (from day -7 to -1, 1.5 mu L/g per day). On day 0, B6 splenocytes were harvested to coculture with Balb/c splenocytes pretreated with mitomycin C in 1-way mixed lymphocyte cultures (MLC). After 48 hours, the proliferation, we measured apoptosis and the CD4(+)CD25(+) T-cell ratio of cultured cells. The heterotopic cardiac transplantation model was performed from Balb/c to B6 using the recipients pretreated with this protocol. On day 0, RPM was withdrawn and the transplantations performed. The mean survival time (MST) of the grafts evaluated and in vitro assays measured. Results. Both in vitro and in vivo, the protocol suppressed the proliferation of splenocytes as well as enhanced apoptosis and the CD4(+)CD25(+) T-cell ratio. The MST of the grafts was 35 +/- 14.4 days. Conclusions. Our study showed that DST combined with RPM prolonged cardiac allograft survival even if we withdrew immunosuppressants after transplantation. This result may be associated with inhibition of T-cell proliferation. We also demonstrated that RPM expanded CD4(+)CD25(+) T cells and increased splenocyte apoptosis.