Tissue-specific differentiation of a circulating CCR9^- pDC-like common dendritic cell precursor

The ontogenic relationship between the common dendritic cell (DC) progenitor (CDP), the committed conventional DC precursor (pre-cDC), and cDC subpopulations in lymphoid and nonlymphoid tissues has been largely unraveled. In contrast, the sequential steps of plasmacytoid DC (pDC) development are less defined, and it is unknown at which developmental stage and location final commitment to the pDC lineage occurs. Here we show that CCR9+ pDCs from murine BM which enter the circulation and peripheral tissues have a common DC precursor function in vivo in the steady state, in contrast to CCR9⁺ pDCs which are terminally differentiated. On adoptive transfer, the fate of CCR9 ^- pDC-like precursors is governed by the tissues they enter. In the BM and liver, most transferred CCR9^- pDC-like precursors differentiate into CCR9⁺pDCs, whereas in peripheral lymphoid organs, lung, and intestine, they additionally give rise to cDCs. CCR9^- pDC-like precursors which are distinct from precDCs can be generated from the CDP. Thus, CCR9^- pDC-like cells are novel CDP-derived circulating DC precursors with pDC and cDC potential. Their final differentiation into functionally distinct pDCs and cDCs depends on tissue-specific factors allowing adaptation to local requirements under homeostatic conditions.