In this study, we adapted our flow cytometry procedure initially developed to quantify intracellular imatinib without modifying (e.g. tagging) the molecule25 in mature cells and CD34+ progenitors/LSC within the same CML sample, and then assessed BCR-ABL protein inhibition in function of nilotinib intracellular concentration. The gene discussed is BCR; the disease is chronic myelogenous leukemia, BCR-ABL1 positive.