Effect of high and low Bcr-Abl expression levels on CD34⁺ cell proliferation, apoptosis, and differentiation. (A) The number of cells generated after culture of control, BA^hi, and BA^lo CD34⁺ cells for 7 days in SFM containing low growth factor was determined. The data shown represent the mean ± SEM fold-cell expansion for 6 individual experiments. Significance values for differences between BA^hi and BA^lo cells is *P < .05. (B) Transduced CD34⁺ cells (n= 4) were labeled with the fluorescent dye SNARF-1 and cultured for 72 hours followed by assessment of SNARF-1 fluorescence by flow cytometry. Each cell division results in a diminution in SNARF fluorescence. (A) Proliferation index (PI) was calculated from the flow cytometry data using ModFit software. Significance value for differences between BA^hi and BA^lo cells is *P < .05. (C) Transduced CD34⁺ cells (n= 5) were cultured in media with or without serum and GF for 48 hours. Cells were labeled with annexin V–Cy-5 and 7-AAD and apoptosis was assessed by flow cytometry. The figure shows total apoptotic cells following culture in serum and GF-containing medium. (D) Total apoptotic cells following culture without serum and GF. Significance values for differences are *P < .003, MIG R1 versus BA^hi; **P < .006, BA^lo versus BA^hi. (E) Transduced CD34⁺ cells (n= 4) cultured for one week in SFM with low GF and analyzed by flow cytometry for erythroid and myeloid differentiation. The figure shows absolute number (log₁₀ scale) of cells expressing the different phenotypic marker generated per 25 000 input cells. Significance value for differences between BA^hi and BA^lo cells is *P < .05, for CD11b, CD33, and glycophorin A.