Prevention of tumor metastasis after surgical removal of primary tumor by using in vitro activated macrophages.

In vitro activation of peritoneal macrophages by Propionibacterium acnes and its immunotherapeutic potential for inhibiting metastasis was investigated. C3H/HeN mouse adherent peritoneal exudate cells as a source of macrophages were treated in vitro with P. acnes. These P. acnes-activated macrophages were tested for tumoricidal activity in vitro and antimetastatic activity in vivo. In vitro cytotoxicity tests revealed that they had potent cytotoxicity. Surgical resection of X5563 tumors in syngeneic C3H/HeN mice 10 days after the tumor implantation failed to rescue the hosts from tumor metastasis despite successful removal of the primary tumor. When the activated macrophages were transferred intravenously into C3H/HeN mice following the surgical operation, an appreciable number of mice survived without exhibiting any sign of metastasis. Thus, these results demonstrate that macrophages can be activated in vitro by utilizing appropriate stimulating reagents, and that these activated macrophages have a potent antimetastatic effect.