Overexpression of cyclin D2 further enhances proliferation of myeloid progenitors stimulated by a combination of multiple cytokines. LSK cells transduced with control- or cyclin D2–containing vectors were cultured in serum-free medium supplemented with SFM (A), or SFM3 and G-CSF (SFM3G) (B). Cell numbers were scored following 7 days and for SFM3G cultures also following 4 and 10 days of incubation. Data in panels A and B are shown as number of cells produced per plated LSK cell and represent mean (SD) values from 6 and 3 experiments, respectively. *P < .05.