CD66b-CD64dimCD115- cells in the human bone marrow represent neutrophil-committed progenitors

Here we report the identification of human CD66b−CD64dimCD115− neutrophil-committed progenitor cells (NCPs) within the SSCloCD45dimCD34+ and CD34dim/− subsets in the bone marrow. NCPs were either CD45RA+ or CD45RA−, and in vitro experiments showed that CD45RA acquisition was not mandatory for their maturation process. NCPs exclusively generated human CD66b+ neutrophils in both in vitro differentiation and in vivo adoptive transfer experiments. Single-cell RNA-sequencing analysis indicated NCPs fell into four clusters, characterized by different maturation stages and distributed along two differentiation routes. One of the clusters was characterized by an interferon-stimulated gene signature, consistent with the reported expansion of peripheral mature neutrophil subsets that express interferon-stimulated genes in diseased individuals. Finally, comparison of transcriptomic and phenotypic profiles indicated NCPs represented earlier neutrophil precursors than the previously described early neutrophil progenitors (eNePs), proNeus and COVID-19 proNeus. Altogether, our data shed light on the very early phases of neutrophil ontogeny.