Initial characterization of a cytokine which induces differentiation and cytolytic activity in HL-60 promyelocytic leukemia cells: evidence that the cytokine is distinct from other known differentiation-active cytokines.

In this paper we report that, like dimethyl sulfoxide (DMSO), retinoic acid (RA), and conditioned medium (CM) from lectin-stimulated mononuclear leukocytes, CM from a human null cell leukemia line (Reh) induces HL-60 promyelocytic leukemia cells to respond in an enhanced manner to phorbol diester (PDE). Furthermore, Reh-CM induces PDE-resistant HL-60-1E3 cells to respond to PDE and lyse target cells. Additionally, both HL-60 and HL-60-1E3 cells exposed to Reh-CM for 3 days produce superoxide anion and express cell surface antigens present on mature mononuclear phagocytes. No colony-stimulating factor (CSF) or interferon (IFN) activity was detected in Reh-CM, and differentiation activity (DA) was not removed from Reh-CM by insolubilized anti-IFN gamma. While Reh-CM is antiproliferative against a panel of cell lines, its spectrum of activity is different than tumor necrosis factor (TNF) alpha, and neither TNF alpha nor TNF beta inhibit proliferation of HL-60-1E3 or induce these cells to respond to PDE. The differentiation factor (DF) material has been partially purified by ammonium sulfate precipitation and is non-dialyzable; unstable to heat, acid, or alkali treatment; and the activity is not blocked by anti-IL-6 or anti-IFN alpha. The data presented in this paper suggest the presence of a differentiation-inducing factor which is distinct from CSF, IFN alpha or -gamma, TNF alpha, or -beta, or IL-6, which may play a role in the differentiation of malignant (leukemic) and normal cells of the myelomonocytic lineage.