ORIGINAL ARTICLE BCR-ABL activity and its response to drugs can be determined in CD34 þ CML stem cells by CrkL phosphorylation status using flow cytometry

stem/progenitor cellsappear resistant to imatinib mesylate (IM) in vitro and in vivo.Toinvestigate the underlying mechanism(s) of IM resistance, it isessential to quantify Bcr-Abl kinase status at the stem cell level.We developed a flow cytometry method to measure CrkLphosphorylation (P-CrkL) in samples with o10