Impact of heterozygous, homozygous, and hemizygous Flt3-ITD expression on myeloid progenitor subsets. (A) Representative FACS analysis of MkP (Lin⁻c-Kit⁺Sca1⁻ [LKS⁻] CD41⁺CD150⁺), GMPs (LKS⁻ CD41⁻CD16/32^hiCD150⁻), CFU-E (LKS⁻ CD41⁻CD16/32^−/low CD150⁻CD105⁺), pre-CFU-E (LKS⁻ CD41⁻CD16/32^−/low CD150⁺CD105⁺), pre-GMPs (LKS⁻ CD41⁻CD16/32^−/low CD150⁻CD105^−/low), and PreMegE (LKS⁻ CD41⁻CD16/32^−/lowCD150⁺CD105^−/low) in the BM of Flt3^+/+, Flt3^ITD/ITD, Flt3^+/ITD, and Flt3^−/ITD and spleen of Flt3^+/+ and Flt3^ITD/ITD mice. Numbers shown are the mean values for the frequencies (percentage of total BM cells) of each progenitor subset from a total of 4-9 male mice for each genotype. (B) Mean (SD) absolute numbers of pre-GMPs and GMPs in the BM and spleen of Flt3^+/+, Flt3^ITD/ITD, Flt3^+/ITD, and Flt3^−/ITD mice (4-9 male mice analyzed for each genotype in at least 2 independent experiments) at 8-9 weeks of age. (C) Single-cell GM colony formation of GMPs from Flt3^+/+ and Flt3^ITD/ITD BM cells. Open bars represent cloning frequencies as established after 8 days of culture; and black bars, frequency of high proliferative clones (covering > 50% of the well). Mean (SD) values from 2 experiments, each in which BM cells from 3-9 mice of each genotype were pooled for FACS sorting. (D) Unfractionated BM and spleen cells from WT, Flt3^+/ITD, Flt3^ITD/ITD, and Flt3^−/ITD mice were plated on methylcellulose supplemented with myeloid promoting cytokines and scored for GM colony formation after 10 days of incubation. Results are mean (SD) values of at least 3 experiments (5-11 mice of each genotype, each performed in duplicate). *P < .05. **P < .01. ***P < .001. (E) Mean (SD) numbers of LSK cells in BM of Flt3^+/+, Flt3^+/ITD, Flt3^ITD/ITD, and Flt3^−/ITD mice. A total of 8-14 mice (8-9 weeks old, of each genotype) were investigated. *P < .05.