Correspondence To

the editor: BCR-ABL expression in leukemic progenitors and primitive stem cells of patients with chronic myeloid leukemia Kumari and colleagues have recently reported a detailed analysis of BCR-ABL expression in CFU-Cs (colony forming units in culture) of patients with chronic myeloid leukemia (CML).1 Using quantita-tive reverse-transcription PCR on individual Ph1 hematopoietic colonies, they demonstrated that CFU-Cs from patients in major molecular response (MMR) displayed lower BCR-ABL mRNA expression than CFU-Cs from patients at diagnosis. In addition, the authors observed a large variability of BCR-ABL/ABL ratios in homogeneous subpopulations of CFU-Cs. These interesting find-ings were evaluated in the progenitor compartment and not in the more primitive stem cell compartment, including long-term-culture initiating cell (LTC-IC)–derived CFU-Cs