Overexpression of Id1 in early HSCs drives myeloid differentiation at the expense of lymphoid development. (A) LSK progenitors were transduced with vector or Id1-expressing retrovirus. Transduced cells were sorted for GFP expression 36 hours later and plated at 2500 cells/well in X-VIVO15 media containing SCF, Flt3-L, and IL-7. After 14 days, cells were harvested and stained with the indicated antibodies and analyzed by flow cytometry. Representative plots are shown for wells containing vector (left) and Id1-transduced cells producing either predominantly Mac-1⁺CD11c⁻ (center) or Mac-1⁺CD11c⁺ cells (right). The proportions of indicated cell populations produced from vector or Id1-transduced progenitors in individual wells are shown in the bar graph below the plots. Data are representative of 3 experiments. (B) CD45.1⁺ bone marrow cells from 5-FU–treated wild-type mice were transduced with vector or Id1-expressing retrovirus. Transduced cells were sorted for GFP expression, and equal numbers of transduced cells were injected into lethally irradiated CD45.2⁺ host mice. Three weeks later, bone marrow cells from transplanted hosts were isolated and analyzed using flow cytometry. GFP expression on donor-derived cells is shown in histograms on the left. Representatives of FACS analyses for indicated markers on gated GFP⁺ cells are shown, and the percentage of cells in each quadrant is indicated. Average numbers of Mac1⁺ and B220⁺ cells/femur derived from vector and Id1-transduced cells are shown in the bar graph with SD (n = 3). Data are representative of 3 experiments.