Clonogenic colony formation and precursor-progeny relationships of myeloerythroid progenitor subsets.

(A) At least 100 wells receiving a single cell from each sorted progenitor population were scored. FcγR^loCD34⁺ cells produced all myeloid colony types, including CFU-GEMMeg, whereas FcγR^loCD34⁻ and FcγR^hiCD34⁺ populations gave rise only to MegE and GM colonies, respectively. (B) One thousand cells from each Lin⁻IL-7Rα⁻c-Kit⁺Sca-1⁻progenitor subset were sorted onto irradiated OP9 stromal layers supplemented with SLF, IL-11, and TPO. (C) Reanalysis of sorted FcγR^loCD34⁺ cells. (D) Culture supernatants were harvested after 48 hours on OP9 and analyzed for myeloid progenitor markers. Lin⁻IL-7Rα⁻c-Kit⁺Sca-1⁻ cells were recovered from cultured FcγR^loCD34⁺ cells, but not from the other 2 progenitor subsets (not shown). FcγR^loCD34⁺ cells generated both FcγR^hiCD34⁺ and FcγR^loCD34⁻ subsets. Recovered FcγR^hiCD34⁺ and FcγR^loCD34⁻ cells were sorted into methylcellulose cultures and differentiated exclusively to either GM or EMeg cell types (not shown). We therefore term FcγR^loCD34⁺ cells FL common myeloid progenitors (CMPs), FcγR^hiCD34⁺ cells FL granulocyte–monocyte-restricted progenitors (GMPs), and FcγR^loCD34⁻ cells FL megakaryocyte–erythrocyte-restricted progenitors (MEPs).