Purified human macrophage secretions suppress tumor growth in the mouse

Purified supernatants obtained from human macrophage supernatants or the U937 human macrophage cell line are cytotoxic for tumor cells in vitro, and when tumor bearing animals are injected with these supernatants tumor growth is suppressed in vivo. Tumor growth rate and survival times were assessed for each group of animals. At day 12 after injection of the P815 tumor cells, no difference in tumor size could be demonstrated in any of the groups. However, by day 17 the tumors in the animals treated with macrophage supernatants or the U937 macrophage cell line supernatants did not continue to increase in size as was seen in the case of the control animals. When examining survival times, it appeared that the animals treated with macrophage supernatants survived approximately 8 days longer than did the animals receiving no treatment (35-day vs 27-day survival), and the animals treated with the U937 macrophage cell line supernatants survived approximately 13 days longer than the control animals (40-day vs 27-day survival). Thus, it appears that tumor cell growth can be slowed down in vivo when purified macrophage supernatants as well as the secretions from a human macrophage cell line are injected into the tumor mass.