Immature and mature CD8α+ dendritic cells prolong the survival of vascularized heart allografts

CD8α + and CD8α − dendritic cells (DCs) arise from committed bone marrow progenitors and can induce or regulate immune reactivity. Previously, the maturational status of CD8α − (myeloid) DCs has been shown to influence allogeneic T cell responses and allograft survival. Although CD8α + DCs have been implicated in central tolerance and found to modulate peripheral T cell function, their influence on the outcome of organ transplantation has not been examined. Consistent with their equivalent high surface expression of MHC and costimulatory molecules, sorted mature C57BL/10J (B10; H2 b ) DCs of either subset primed naive, allogeneic C3H/HeJ (C3H; H2 k ) recipients for Th1 responses. Paradoxically and in contrast to their CD8α − counterparts, mature CD8α + B10 DCs given systemically 7 days before transplant markedly prolonged B10 heart graft survival in C3H recipients. This effect was associated with specific impairment of ex vivo antidonor T cell proliferative responses, which was not reversed by exogenous IL-2. Further analyses of possible underlying mechanisms indicated that neither immune deviation nor induction of regulatory cells was a significant contributory factor. In contrast to the differential capacity of the mature DC subsets to affect graft outcome, immature CD8α + and CD8α − DCs administered under the same experimental conditions significantly prolonged transplant survival. These observations demonstrate for the first time the innate capacity of CD8α + DCs to regulate alloimmune reactivity and transplant survival, independent of their maturation status. Mobilization of such a donor DC subset with capacity to modulate antidonor immunity may have significant implications for the therapy of allograft rejection.