Effect of IM on growth of TF-1 BCR/ABL cell line expressing high and low levels of Bcr-Abl. (A) TF-1 hematopoietic cells were transduced with MIG R1 and MIG 210 retrovirus as described in “Patients, materials, and methods.” GFP-low (TF-1-BA^lo) and GFP-high (TF-1-BA^hi) populations were selected from MIG 210–transduced cells by flow cytometry sorting as shown. A single GFP⁺ population was selected from MIG R1–transduced cells. Cells were maintained with 2 ng/mL GM-CSF. (B) Bcr-Abl protein expression in transduced cells was assessed by Western blotting using anti-Abl antibodies. Blots were reprobed with an antiactin antibody to check sample loading. A representative blot is shown. The ratio of intensity of Bcr-Abl to actin for TF-1 BA^lo and TF-1 BA^hi cells from multiple experiments was 0.44 ± 0.20 and 0.93 ± 0.13, respectively (n= 4, P < .012). (C-D) TF1-1/GFP⁺ cells were plated at density of 10 000 cells/well in absence of GM-CSF or in presence of 1 ng/mL GM-CSF in the presence of graded concentrations of IM as shown and viable cells present after 72 hours culture assessed in a MTS assay. The results shown represent 3 independent experiments in which each experimental point was the mean of triplicate determinations. Significance levels comparing BA^lo versus BA^hi cells are *P= .078; **P= .025; and ***P= .056.