Ectopic expression of Id2 inhibits monocyte generation. CD34⁺ cord-blood cells were transduced with vectors encoding Id2-IRES-GFP or PU.1-IRES-GFP and were then stimulated in serum-free medium supplemented with cytokines as indicated. Vitamin D3 (VD3) was added as indicated. Cells were harvested at day 7 and stained for CD11b versus CD14. GFP⁺ cells were gated in a separate FACS diagram (not shown). Representative CD11b versus CD14 analyses of gated GFP⁺ cells (Id2-IRES-GFP, empty control vector, or PU.1-IRES-GFP) are shown (top: SCF/Flt3L/M-CSF/IL-6; bottom left: SCF/Flt3L/GM-CSF/TNFα; bottom right: SCF/Flt3L/vitamin D3). The data are representative of 3 independent experiments. The number in each quadrant indicates the percentage of cells in that quadrant.