Granulocyte-monocyte progenitors (GMPs) differentiate into myeloid DCs in the presence of GM-CSF or differentiate into regulatory DCs in the presence of VIP or the combination of IL-10 and TGF-β. CD4⁺ and CD8⁺ T_reg cells with regulatory DCs inhibit the inflammation, autoimmunity, and GVHD that result from T cells stimulated by myeloid DCs.