INTERACTIONS BETWEEN HUMAN MACROPHAGES AND TUMOR-CELLS IN 3-DIMENSIONAL CULTURES

Human blood mononuclear cells were cultured for 7 days in hydrophobic plastic bags. Macrophages differentiated from monocytes and purified b y elutriation were then cocultured with round-shaped aggregates of epi thelial cells (spheroids). Spheroids prepared from the SK-MES-1 carcin oma cell line were cultured individually, under constant stirring, in multiwell plates coated with agarose. Macrophage/spheroid interactions were investigated under various experimental conditions. Macrophages activated with interferon gamma aggregated to each other and to sphero ids, in contrast to control unactivated macrophages. Histological exam ination, after staining with a macrophage-specific monoclonal antibody , showed that bath control and interferon-gamma-activated macrophages migrated between epithelial tumor cells and infiltrated the spheroids. The addition of anti-ICAM-1 monoclonal antibody inhibited macrophage homotypic aggregation as well as aggregation to and penetration into s pheroids. The macrophages did not exert cytolytic effects, as judged b y a chromium-51 release assay, but provoked a diminution of tritiated thymidine incorporation by tumor cells. Cytostatic activity was observ ed with effector:target ratios as low as 1:16, and was maximal (99% at a 1:1 E:T ratio) with macrophages differentiated in the presence of g ranulocyte/macrophages-colony-stimulating factor. The cytostatic effec t was not related to tumor necrosis factor alpha secretion.