Identification of a CD117+​ ​CD71+​ ​ early ​unipotent​ neutrophil progenitor population in human bone marrow. 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. Overall design: Expression profiling by high throughput sequencing for sorted neutrophils cells in human bone marrow