Single-cell omics reveal human GM-CSF-dependent mononuclear phagocyte subsets in humanized mice

Dendritic cells (DC) are antigen presenting cells controlling T cell activation. In human, the diversity, ontogeny and functional capabilities of DC subsets are not fully understood. Here, we identified circulating CD88-CD1c+CD163+ DC (termed as DC3) as an immediate precursor of inflammatory CD88-CD14+CD1c+CD163+FceRI+ DC. DC3 develop via a specific pathway, independent from the cDC-restricted (CDP) and monocyte-restricted (cMoP) progenitors, and are activated by GM-CSF. As classical DC, but unlike monocytes, DC3 drove the activation of naïve T cells. In vitro, DC3 displayed a distinctive ability to prime CD8+ T cells expressing a tissue-homing signature and the epithelial homing alpha-E integrin (CD103) through transforming growth factor-b (TGF-ß) signaling. In vivo, DC3 infiltrated luminal breast cancer primary tumors and DC3 infiltration correlated positively with CD8+CD103+CD69+ tissue-resident memory T cells. Altogether, these findings define DC3 as a lineage of inflammatory DC endowed with a strong potential to regulate tumor immunity. Overall design: 3 independent immunodeficient NSG mice were injected intravenously with B16 producing human GM-CSF. Lung metastasis bearing mice were engrafted with 3 independent human PBMCs. Human CD45+ cells were isolated from metastatic mouse lungs. Sorted cells from each mouse were pooled together and CD1c+ and CD14+ cells were mixed at 80:20 ratio.