Host-derived CD8⁺ dendritic cells protect against acute graft-versus-host disease after experimental allogeneic bone marrow transplantation.

Graft-versus-host disease (GVHD) is a frequent life-threatening complication after allogeneic hematopoietic stem cell transplantation (HSCT) and induced by donor-derived T cells that become activated by host antigen-presenting cells. To address the relevance of host dendritic cell (DC) populations in this disease, we used mouse strains deficient in CD11c(+) or CD8α(+) DC populations in a model of acute GVHD where bone marrow and T cells from BALB/c donors were transplanted into C57BL/6 hosts. Surprisingly, a strong increase in GVHD-related mortality was observed in the absence of CD11c(+) cells. Likewise, Batf3-deficient (Batf3(-/-)) mice that lack CD8α(+) DCs also displayed a strongly increased GVHD-related mortality. In the absence of CD8α(+) DCs, we detected an increased activation of the remaining DC populations after HSCT, leading to an enhanced priming of allogeneic T cells. Importantly, this was associated with reduced numbers of regulatory T cells and transforming growth factor-β levels, indicating an aggravated failure of peripheral tolerance mechanisms after HSCT in the absence of CD8α(+) DCs. In summary, our results indicate a critical role of CD8α(+) DCs as important inducers of regulatory T cell-mediated tolerance to control DC activation and T cell priming in the initiation phase of GVHD.