Most in vivo reconstituting murine stem cells proliferate in response to KL + IL-3 + IL-6 as well as KL + FL + MGDF. CFSE-stained Lin⁻Sca1⁺c-kit⁺(Ly5.1) BM cells were cultured in SF-medium supplemented with either K36 (A) or KFM (B) (all at 50 ng/mL, except for IL-3 at 20 ng/mL). (A) and (B) show the proliferation history (number of cell divisions) after 7 days of incubation. Cultured CFSE-stained cells were resorted to include either all cells (total) or only cells that had proliferated (a conservative approach was taken to only include cells that had undergone ≥2 divisions). Both cell populations, as well as the unexpanded CFSE-stained cells (control), were transplanted into lethally irradiated mice (C) together with unfractionated BM cells (Ly5.2). Analysis of the percentage of total donor reconstitution in peripheral blood was performed 6 and 16 weeks posttransplantation. Control and expanded cell populations showed comparable repopulation of all (myeloid, B, and T) lineages. All data are the means (±SEM) of 4 mice, except for KFM (total) 16 weeks posttransplantation, where n = 3. Data are from 1 of 2 experiments with similar results.