Loss of growth factor independence by cultured BCR-ABL–transduced IL-3^−/− cells.

(A) Growth of cells from expanded clones of BCR-ABL–transduced (diamonds), IL-3^−/− (left panel) and +/+ BM cell cells (right panel) in the presence (solid symbols) and absence (open symbols) of exogenous factors (SF and IL-6) compared with data for clones derived from IL-3^−/− or +/+ cells cotransduced with BCR-ABL and IL-3 (triangles). Viable cell numbers were determined by hematocytometer counts of trypan blue–excluding cells. Results are expressed as the mean fold-changes compared with input values (± SEM) from 3 independent experiments. (B) DNA profiles of PI-stained cells from representative expanded clones of BCR-ABL–transduced +/+ (left), IL-3^−/− (middle), and BCR-ABL– and IL-3–cotransduced IL-3^−/− cells (right) assessed after their maintenance for 7 days in the absence of growth factors. Percentage of apoptotic cells (M1) in the G₀/G₁ (M2) and S/G₂/M (M3) phases of the cell cycle were determined using the Cell Quest software (Becton Dickinson).