Effect of IM on growth of CD34⁺ cells expressing high and low levels of Bcr-Abl. (A) The number of viable cells present after culture of CD34⁺GFP⁺ cells for 72 hours with or without IM (0.05-1.0 μM) was determined using an MTS assay. The results shown were obtained from 3 independent experiments in which each experimental point was the mean of triplicate determinations. Significance levels are *P < .001; **P < .005; ***P < .05; and ****P < .016, BA^lo versus BA^hi. (B) Cell division of CD34⁺GFP⁺ cells after culture for 72 hours with or without IM (0.1 and 1.0 μM) was measured using a SNARF-1 labeling assay as described in “Patients, materials, and methods.” A PI was determined using ModFit software. Significance level for BA^lo versus BA^hi in presence of 0.1 μM and 1.0 μM IM is *P < .001. (C) Apoptosis of CD34⁺GFP⁺ cells after culture for 72 hours with or without IM (0.1 and 1.0 μM) was measured using annexin V–Cy5 and 7-AAD labeling and was analyzed by flow cytometry. The data shown represent the mean ± SEM values of results for 5 experiments. Significance levels for BA^lo versus BA^hi in presence of 0.1 μM and 1.0 μM IM are *P < .002 and **P < .009, respectively.