Cell cycle characteristics, phagocytosis and maturation of immature white blood cells from seven patients with Ph1-positive chronic myelocytic leukemia were studied in vitro. In five patients whose cells contained only one Ph1 chromosome there were two in early stable phase, one in transitional phase, and two in blastic crisis. The other two patients had cell lines with more than one Ph1 chromosome in addition to cells containing one Ph1 chromosome. Cell cycle times in the seven patients as determined with tritiated thymidine ranged from 48 to 59 hr regardless of stage of the disease with one exception (32 hr in a patient who died within 1 wk). A small percentage of myeloblasts was arrested in early S or G2 for the duration of the study of up to 1 wk. Maturation in vitro was observed with appearance of the first labeled metamyelocytes at 2 hr and first labeled mature segmented and nonsegmented neutrophils at 10 hr (with the median time of 22 hr of in vitro culture). Results of this study suggest that cell precursors in blastic transformation have a diminished capability to mature despite the early presence of mature neutrophils in vitro. Early appearance of labeled mature neutrophils and irregularity of the time sequence are characteristic of cells from patients in blastic transformation. Immature granulocytic precursors were shown capable of phagocytosis in vitro, suggesting that although nuclear maturation was delayed, membrane and cytoplasmic function was intact. This dissociation may be characteristic of leukocytes from patients with chronic myelocytic leukemia.

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