FLOW-CYTOMETRIC ANALYSIS OF IN-VIVO INDUCTION OF DIFFERENTIATION OF WEHI-3B MYELOMONOCYTIC LEUKEMIA-CELLS BY RECOMBINANT GRANULOCYTE-COLONY-STIMULATING FACTOR

An animal leukemia model was developed to investigate in vivo inductio n of differentiation of myeloid leukemia cells. An aneuploid cell line (C15) was isolated from mouse myelomonocytic leukemia WEHI-3B D+ cell s. The C15 cells contained twice as much DNA as the parental cells but retained the morphology of myelomonocytic cells and the ability to di fferentiate into macrophage-like cells in response to all-trans retino ic acid (ATRA) in vitro. When the C15 cells were inoculated into the p eritoneal cavity of syngeneic Balb/c mice (106 cells/mouse), the mice died of leukemia within 19 days. The DNA content and differentiation a ntigen (Mac-1) of the cells in the peritoneal cavity were determined b y dual-parameter flow cytometry. On day 12 after inoculation, the C15 cells were distinguishable from normal host cells in the peritoneal ca vity by their different DNA content. The administration of recombinant human granulocyte colony-stimulating factor (rhG-CSF) (10 mu g/day) t o mice bearing C15 cells induced the leukemia cells to express Mac-1 a ntigen and to change morphologically into mature granulocytic cells. B ecause the C15 cells were not responsive to G-CSF in suspension cultur e in vitro, this result suggests that the cytokine's actions on the ce lls in vivo and in vitro are different. This experimental model for an alyzing in vivo differentiation of leukemia cells will be useful for s tudying the therapeutic effects of potential differentiation-inducing agents.