The effects of imatinib mesylate are not mediated by induction of apoptosis. Mobilized human CD34⁺ progenitors were cultured in the presence of GM-CSF, TNF-α, IL-4, and FLT3L with or without imatinib mesylate in concentrations varying from 1 to 5 μM. The viability of the cell populations and rate of apoptosis induction were analyzed by annexin V FITC and propidium iodide staining in a flow cytometer. The percentages of necrotic or apoptotic cells are indicated in the corresponding quadrants.