Identification of a CD117+​ ​CD71+​ ​ early ​unipotent​ neutrophil progenitor population in human bone marrow

Neutrophils play critical roles in health and disease. Due to their very short half-life in blood and tissue, neutrophils are constantly replenished by bone marrow progenitors. Thus, a comprehensive understanding of bone marrow neutrophil development is of paramount importance to identify how neutrophil production is altered in disease. Recently, two novel human neutrophil progenitor populations were identified; ‘human neutrophil progenitor’ or ‘hNeP’ (Lin-​ ​CD66b+​ ​CD117+​ ​) ​and ‘neutrophil precursor’ or ‘preNeu’ (Lin-​ ​CD66b+​ ​CD15+​ ​CD49d+​ ​). How these subsets fit into the neutrophil lineage is unclear. By using mass and flow cytometry, we show that hNeP are a heterogenous population containing a homogeneous progenitor subset termed ‘early neutrophil progenitor’ or ‘eNeP’ (Lin-​ ​CD66b+​ ​CD117+​ ​CD71+​ ​). ​Surface marker and RNA expression, together with the ability to form colonies ​in vitro and exclusively produce neutrophils ​in vivo in humanized NSG-SGM3 mouse transfer experiments indicate that eNeP are hierarchically the ‘earliest’ cells within preNeu. eNeP constitute ~0.14% of human bone marrow neutrophils, while preNeu constitute ~5% of bone marrow neutrophils. Furthermore, we have identified CD71 as a novel neutrophil surface marker associated with distinct early neutrophil developmental stages. Intriguingly, CD71+​ characterizes proliferating neutrophils, which are expanded in the blood of melanoma and lung cancer patients and detectable in human lung tumors. Collectively, our findings i) identify CD117+​ ​CD71+​ ​eNeP as an early neutrophil progenitor population, ii) introduce a unified model of human neutrophil bone marrow development, iii) identify novel surface markers for distinct neutrophil developmental stages and iv) provide evidence for neutrophil progenitor expansion in cancer. Expression profiling by high throughput sequencing for sorted neutrophils cells in human bone marrow