M-CSF AND 1,25-DIHYDROXY-VITAMIN-D-3 SYNERGIZE WITH 12-O-TETRADECANOYLPHORBOL-13-ACETATE TO INDUCE MACROPHAGE DIFFERENTIATION IN ACUTE PROMYELOCYTIC LEUKEMIA NB4 CELLS

NB4 cells were derived from a patient with acute promyelocytic leukemi a (APL) and, unlike HL-60 cells, display the characteristic translocat ion t(15:17) involving the RAR alpha receptor. NB4 cells differentiate into granulocytes in response to all-trans retinoic acid, but little is known about the ability of these cells to form monocytes and macrop hages. We show here that NB4 cells treated individually with a variety of agents, including recombinant human macrophage colony-stimulating factor (M-CSF), 1,25 dihydroxy vitamin D-3 (1,25 D-3) or 12-O-tetradec anoylphorbol-13-acetate (TPA), resulted in only partial or incomplete differentiation along the monocyte/macrophage pathway. However, when M -CSF was combined with TPA, or 1,25 D-3 with TPA, a synergistic respon se was observed such that differentiation to fully functioning monocyt es or macrophages occurred. In contrast, 1,25 D-3 with M-CSF resulted in only a modest increase in the number of non-specific esterase posit ive cells and no increase in the phagocytic activity (ingestion of lat ex beads) when compared to either agent alone. We suggest that IPA and 1,25 D-3 are monocyte/macrophage-specific differentiation inducing ag ents in NB4 cells but that both are required to achieve optimal macrop hage function. We suggest a model for the synergistic action of TPA an d 1,25 D-3 and propose that inducing monocytic differentiation could a lso be considered in designing clinical protocols for the treatment of acute leukemia.