Expanded progeny cells of diffuse cytotoxic bone marrow-derived colonies

Bone marrow-derived (colony-stimulating factor [CSF]-dependent) diffuse colonies have been shown to include colonies with cytotoxic activity. Such diffuse colonies were expanded for 6-8 weeks in liquid culture medium in the presence of pokeweed mitogen- or concanavalin A-conditioned spleen cell medium (CM). The morphology of the expanded diffuse colony cells (EDCC) was like that of early myelocytic cells. EDCC lost their cytotoxic capacity when expanded, but the cytotoxicity could be reinduced by pretreatment of the colonies with interferon or phorbol ester. Traditional sources of mouse or human CSF such as lung CM, placenta CM and human mononuclear cell CM did not support proliferation of EDCC, whereas partly purified interleukin-3 (IL-3), lacking CSF and IL-2, was stimulatory for EDCC. Thus, the stimulatory factor for EDCC was not CSF but a factor closely related to IL-3. Monoclonal antibodies against T lymphocytes or macrophages did not bind to EDCC. EDCC did not have Fc receptors, but 10% of the cells were positive for a monoclonal anti-Ia antibody. All EDCC were positive for alpha NAE and NASDCI esterases but negative for acid and alkaline phosphatases and peroxidase reactivity; less than 2% of the cells showed metachromatic staining with toluidine. Ultrastructurally, EDCC showed various degrees of cell differentiation but absence of specific cytoplasmatic characteristics such as neutrophilic, eosinophilic, basophilic and mast cell granules. Current work aims to define factors and conditions necessary for the induction of differentiation in these immature monomyelocytic cells.