G-CSF and GM-CSF are clinically relevant therapeutics for treatment of acquired and congenital neutropenia and for chemotherapy- or irradiation-induced neutropenia, respectively.37 A1 is likely involved in the therapeutic effect of GM-CSF on progenitors and differentiated cells, whereas the G-CSF-mediated pro-survival effect probably is rather Mcl-1 dependent then A1 dependent. Here, CSF2 is linked to severe congenital neutropenia.