Long-term survival of limb allografts induced by pharmacologically conditioned, donor alloantigen-pulsed dendritic cells without maintenance immunosuppression

Background. We showed recently that limb allograft survival could be enhanced by administration of alloantigen (Ag)-pulsed immature dendritic cells (DC) after transplantation. Since indefinite graft survival was not achieved, we have further modified the DC by pharmacologic (rapamycin; Rapa) conditioning and ascertained their influence on graft survival, without continued immunosuppressive therapy. Methods. We compared the ability of donor Ag-pulsed, Rapa-conditioned rat myeloid DC (Rapa DC) and control DC (CTR DC) to inhibit alloreactive T-cell responses after limb transplantation in antilymphocyte serum (ALS)-treated recipients given a short postoperative course of cyclosporine (CsA). Results. Both DC populations expressed similar levels of major histocompatibility complex (MHC) II, CD40 and CD54, but Rapa DC expressed lower CD86. After toll-like receptor activation, both populations produced minimal interleukin (IL)-12p70, but Rapa DC secreted lower levels of IL-6 and IL-10. The capacity of DCs to stimulate T-cell proliferation in mixed leukocyte reactions was very low. Pulsing of the DC with donor Ag did not alter their phenotype or function. Interestingly, posttransplant administration of donor Ag-pulsed Rapa DC to rats given perioperative ALS and 21 days CsA significantly delayed graft rejection and promoted long-term (> 125 days) graft survival. AlloAg-pulsed Rapa DC induced T-cell hyporesponsiveness and promoted the generation of IL-10-secreting CD4(+) T cells upon ex vivo challenge. Conclusions. Infusion of donor Ag-pulsed, Rapa-conditioned DC after composite tissue transplantation can prevent rejection of the grafts, including skin, across a full MHC mismatch and in the absence of continued immunosuppressive therapy.