BCR-ABL EXPRESSION IN DIFFERENT SUBPOPULATIONS OF FUNCTIONALLY CHARACTERIZED PH(-LEUKEMIA() CD34(+) CELLS FROM PATIENTS WITH CHRONIC MYELOID)

In patients with chronic myeloid leukemia (CML), the leukemic (BCR-ABL (+)/Ph(+)) clone typically includes cells belonging to all of the myel oid lineages and frequently some B cells. From such observations it ha s been inferred that the initial BCR-ABL gene rearrangement event occu rs in a pluripotent hematopoietic stem cell and that the clone subsequ ently generated is maintained by a subpopulation of neoplastic, BCR-AB L-expressing cells that retain at least some of the defining propertie s of normal hematopoietic stem cells. To test this hypothesis directly , we isolated various subpopulations of CD34(+) cells from fresh or cr yopreserved samples of peripheral blood from 5 CML patients with high white blood cell counts, 4 of which were selected because of their exc lusive content of Ph(+) progenitors (both colony-forming cells and lon g-term culture-initiating cells [LTC-IC]). Cells in each of the CD34() subpopulations isolated were examined for the presence of BCR-ABL mR NA using a reverse transcriptase-polymerase chain reaction technique t hat reproducibly gave a positive signal from single K562 cells. BCR-AB L mRNA was detected in 117 of 147 samples (80%) in which actin mRNA wa s demonstrable. This included 60% to 90% of a large number of individu ally analyzed CD34(+) cells including 46 single CD34(+)CD71(-)CD38(-) cells and 27 single CD34(+)CD71(+)CD38(+) cells from 3 patients. In 2 of these cases, the same populations also contained a very high freque ncy of Ph(+) LTC-IC. Our findings demonstrate BCR-ABL gene expression in neoplastic cells with functional as well as surface marker characte ristics of very primitive normal hematopoietic cells. This implicates the BCR-ABL gene product directly in the acquisition by these cells of properties that alter their interactions with the microenvironment an d deregulate their proliferation control. (C) 1996 by The American Soc iety of Hematology.