REGULATION OF BONE-MARROW MYELOBLAST PROLIFERATION IN CHRONIC MYELOID LEUKEMIA

Abstract

The in vitro [3H]thymidine-labeling index of bone marrow myeloblasts and myelocytes was determined for 9 hematologically normal individuals and 20 Ph1[Philadelphia chromosome]positive chronic myeloid leukemia (CML) patients in the chronic phase of their disease. The mean labeling index of myeloblasts from CML patients when the white blood cell (WBC) count was lower than 20,000/mm3 (42.4%) was not significantly different from that of normal myeloblasts (49.9). This index was significantly (P < 0.05) decreased to an average of 20.9% when the WBC count was higher than 40,000/mm3. The mean labeling index of CML myelocytes was not significantly influenced by the level of WBC. The data presented indicate that such variations in the labeling index of leukemic myeloblasts represent changes of their proliferative activity related to the level of WBC. The proliferation of CML myeloblasts is sensitive, to a certain degree at least, to the size of the myeloid cell population in the body or a subclass of it.