5-FLUOROURACIL-RESISTANT CD34(-POPULATION FROM PERIPHERAL-BLOOD OF CML PATIENTS CONTAINS BCR-ABL-NEGATIVE PROGENITOR CELLS() CELL)

Despite the marked expansion of leukemic cells observed in the hematop oietic system of chronic myeloid leukemia (CML) patients, there is cli nical and experimental evidence that normal nonclonal cells persist in the bone marrow (BM) and peripheral blood (PB) of patients in the ear ly chronic phase. In this study, we attempt to select the benign proge nitor-enriched population from the PB of CML patients. The CD34(+) cel ls isolated from the PB of 12 CML patients in the chronic phase were t reated with low doses (5 or 10 mu g/mL) of 5-fluorouracil (5-FU). We e xpanded these cells for 7 days in liquid cytokine-mediated cultures. T his expansion in the presence of interleukin-1 (IL-1) plus stem cell f actor (SCF) plus IL-3 or leukemia inhibitory factor (LIF) plus SCF plu s IL-3 seemed at least to preserve the initial clonogenic potential of CD34(+) and 5-FU-resistant CD34(+) cells. For the presence of BCR-ABL , mRNA from each of the 12 patients was studied by reverse-transcripta se-polymerase chain reaction (RT-PCR) on 10-15 pooled CFU-GM colonies plucked from methylcellulose cultures of starting and expanded populat ions. Although all PCR results were positive for colonies harvested be fore liquid culture, we were able to identify BCR-ABL-negative colonie s from an expanded CD34(+) population cultured in the presence of reco mbinant cytokines in 11 of 12 patients studied. 5-FU pretreatment of C ML CD34(+) cells markedly reduced their clonogenic potential and growt h factor-mediated cell proliferation but favored higher frequency of B CR-ABL-free colonies. In conclusion, these data show that 5-FU-resista nt CD34(+) cells from the PB of CML patients contain normal progenitor cells, which can be selected and expanded in short-term cytokine-medi ated cultures.