Inhibition of CRKL phosphorylation in CML CD34⁺ cells by imatinib treatment. CML (n = 6) and normal (n = 3) CD34⁺ cells (2 × 10⁵) were exposed to imatinib (1 and 5 μM) for 16 hours in medium containing low concentrations of growth factors as described in “Patients, materials, and methods.” Whole-cell lysates were electrophoresed on 10% SDS-PAGE and Western blotted with an anti-CRKL antibody. P-CRKL could be distinguished from nonphosphorylated CRKL by its slower migration. (A) Representative results for 2 CML samples and a normal control sample are shown. (B) Densitometry analysis was performed, and the percentage of phosphorylated CRKL determined as described in “Results.” Means ± SEM of P-CRKL/CRKL ratios for treated cells expressed relative to controls are shown for CML (▪) and normal (▦) samples. Significant differences in paired t tests for treated CD34⁺ cells compared with untreated controls are indicated (^*P < .005).