Human monocyte tumouristatic ability: modulation by cytokines and tumour cell products

The ability of human monocytes to exert cytostatic effects against a murine mastocytoma was assessed. Furthermore, the capacity of different cytokines to endow monocytes with tumouristatic activity was investigated. Overall, our results suggest that human monocytes have a rather high baseline tumouristatic ability against tumours but this varied with experimental conditions, notably the effector to target ratio. This baseline activity was enhanced by treatment with a variety of cytokines, notably interferon-gamma, tumour necrosis factor alpha and granulocyte-macrophage colony stimulating factor. As described in other systems, the best positive results were obtained when combinations of cytokines were used, when synergistic effects were evident. Of interest was the fact that treatment of monocytes with tumour cell products diminished their ability to exert tumouristatic effects against the murine mastocytoma. The importance of these findings to tumour growth in vivo is discussed.