The number of circulating granulocytic stem cells (CFU-C) was determined by the in vitro methylcellulose technique in cancer patients receiving intermittent chemotherapy. In 17 patients studied prior to therapy, the median CFU-C concentration per 2 X 10(5) mononuclear cells plated was six, compared to a posttreatment median of 23 in 21 patients (p less than 0.001). Large numbers of stem cells were obtained by leukopheresis and cryopreserved with a 99.5% median CFU-C recovery. Cyclical changes in the concentration of stem cells with maximum values of 20 times baseline were demonstrated in a patient studied at weekly intervals during multiple courses of treatment. It was estimated that, at peak CFU-C concentrations, a quantity of stem cells equivalent to that present in a bulk bone marrow harvest could be obtained from the peripheral blood by a 17-liter pheresis. These results suggest that it may be practical to obtain an adequate number of stem cells from the peripheral blood to study autologous stem cell infusion as a means of averting myelosuppression in patients receiving intensive chemotherapy.

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