In contrast, constitutive deletion of Gfi1 leads not only to a complete loss of HSCs' stemness (27), but also to a severe neutropenia accompanied by accumulation of immature monocytic cells both in the BM and PB (29), suggesting that GFI1 and GFI1B may function biochemically in a similar way, but since they exert these functions in different cell types, have also very different biological roles. This evidence concerns the gene GFI1 and neutropenia.