Retention but significant reduction of BCR-ABL transcript in hematopoietic stem cells in chronic myelogenous leukemia after imatinib therapy

Chronic myelogenous leukemia (CML) is effectively treated with imatinib mesylate (IM), a small molecule inhibitor of the BCR-ABL tyrosine kinase that is expressed in the entire hematopoietic compartment including stem cells (HSC) and progenitors in CML patients. While IM induces disease remission, it does not appear to eradicate BCR-ABL-positive stem cells. We investigated the residual CML cells in HSC and myeloid progenitors isolated using fluorescence-activated cell sorting after IM-therapy. Quantitative real-time polymerase chain reaction detecting BCR-ABL transcripts showed that CML progenitors were eradicated within 12 months while the BCR-ABL-positive HSC remained. However, IM-therapy continuation could significantly decrease the ratio of BCR-ABL to BCR also in the HSC population. Our results implicate that the sorted and purified stem cells are useful for more sensitive quantification of BCR-ABL-positive minimal residual disease.