Effects of IM treatment on growth of CD34⁺ cells expressing kinase-domain mutant BCR/ABL genes. CD34⁺ cells were transduced with retroviral vectors expressing the M351T and E255K BCR/ABL kinase-domain mutant genes and CD34⁺GFP^lo (M351T low and E255K low) and CD34⁺GFP^hi (M351T high and E255K high) cells were selected as shown for MIG 210–expressing cells in Figure 1A. (A) The number of viable cells present after culture of M351T- and E255K-expressing cells for 72 hours with or without IM (0.05-1.0 μM) was determined using an MTS assay. Significance levels are for M351T^lo versus M351T^hi were *P < .010 and **P < .101; n= 3. (B) Cell division of M351T- and E255K-expressing cells (n= 4) after culture for 72 hours with or without IM (0.1 and 1.0 μM) was measured using a SNARF-1 labeling assay. Significance levels are shown for 1.0 μM IM: *P < .018, comparing M351T^lo and M351T^hi. (C) Apoptosis of M351T- and E255K-expressing cells (n= 4) after culture for 72 hours with or without IM (0.1 and 1.0 μM) was measured by annexin V–Cy5 and 7-AAD labeling and flow cytometry. Significance levels are shown for 1.0 μM IM: *P < .009, comparing M351T^lo and M351T^hi.