Cytotoxic activity of human blood monocytes against cultured breast cancer cells.

Cytotoxic activity of blood monocytes from 19 healthy individuals was examined in vitro against the cultured floating cells of human breast cancer origin. Target tumor cells inoculated on monocyte cultures and maintained for 5 days were reduced in number, compared with the control cultues of tumor cells alone. Increased cytotoxicity of the monocytes was noted after in vitro activation by heat-killed Corynebacterium liquefaciens (Propionibacterium acnes). C. liquefaciens of the same dose as used for monocyte activation had no effect on the tumor cell growth. These results may indicate that blood monocytes have an antitumor activity and it can be strengthened by treatment with C. liquefaciens. Antitumor activity of blood monocytes and macrophages was discussed on a concept of the mononuclear phagocyte system. A possible development of a new assay method for macrophage function as a parameter of host defence state against cancer will be expected.