578 SURFACE MARKERS AND RNA CONTENT OF LEUKEMIC BLASTS IN ACUTE MYELOID LEUKEMIA OF CHILDHOOD AS A MEASURE OF STAGE OF MATURATION

Abstract

Peripheral blood and bone marrow myeloid cells from 5 children with acute myeloid leukemia were examined using a panel of surface markers and by flow cytofluometry. DNA and RNA content of individual blast cells were measured using acridine orange as a dye. RNA content of leukemic blasts from all 5 patients was higher compared to normal peripheral blood lymphocytes. Eighty-one to 85% of blast cells from 2 of 5 children had IgG Fc receptors and 14-28% of blast cells phagocytized latex particles in vitro. By contrast, the 3 remaining patients had only 11-40% blast cells which had IgG Fc receptors and only 1-3% cells ingested latex particles in vitro. Receptors for complement (C3) were present on 1-6% of the blast cells from each of the 5 patients. The high RNA content of leukemic blasts probably indicates that these cells represent a malignant deviation representing a maturation arrest of myeloid cells at an early stage of differentiation. The expression of IgC Fc receptors and the phagocytic property of blast cells in the present study demonstrate that there exists heterogeneity of the cells involved in acute leukemia of childhood and that this heterogeneity is reflected in the presence of blast cells representing different stages of maturation along the myeloid cell line. (Supported in part by fellowships from the Deutsche Forschungsgemeinschaft, J.M. Foundation and NIH grants CA-17404, CA-19267 and AI-11843)