Comparison of the effect of IM in vitro on different subtypes of CD34⁺ cells from IM responders and nonresponders. (A) Comparison of the effect of 5μM IM on the ability of different subtypes of CFCs in unmanipulated CD34⁺ CML cells from IM responders and nonresponders to form colonies in vitro (same experiments and method of data calculation as shown in the middle panel of Figure 1). Differences between the results for BFU-E and CFU-GM from IM responders and nonresponders are significant (P ≤ .005). (B) The effect of 5μM IM on the patient-specific yield of CFCs in 3-week liquid suspension cultures initiated with the same cells as plated directly in methylcellulose in panel A. (♦) Results obtained from the 3 patients who rapidly developed BC. No significant differences were found between the effect of IM on CFC production in 3-week cultures initiated with CD34⁺ cells from the 2 patient groups (P = .33). In both panels, cross bars represent the mean plus or minus SEM of data for each patient group.