Treatment schedule followed in the study. CD34-positive cells from healthy individuals and Ficoll-gradient-purified myeloid progenitors from patients with CML were either left untreated (NT) or exposed to 10 μM IM (solid arrow) for 24 hours, 10 nM LMB (dashed arrow) for 12 hours, or a combination of the 2 drugs (I+L). In this case, cells were kept for 24 hours in IM, and LMB was added for the last 12 hours. At the end of each treatment cells were washed free of drugs and plated in triplicates in methylcellulose.