Specifically Activated Macrophages Inhibition of Pulmonary Metastasis by Intravenous Injection of Updated Version

SUMMARY The ability of syngeneic macrophages from C57BL/6 mice bearing a progressively growing B16 melanoma to in hibit established pulmonary métastasesin vivo was stud ied. Macrophages were cultured in vitro with supernatants obtained from cultures of B16 tumor cells alone or tumor cells and either normal, nonspecifically sensitized or spe cifically sensitized xenogeneic (rat) lymphocytes. The dif ferent groups of in v/'/ro-treated macrophages were injected i.v. or i.p. into other C57BL/6 mice that had been given i.v. injections of 10,000 viable B16 melanoma cells 48 hr previ ously. The data demonstrated that specifically in v/iro-treated macrophages injected i.v. but not i.p. into mice signifi cantly reduced their number of established pulmonary métastases. Moreover, it appeared that the in vivo inhibi tion of tumor nodules was continuing at the time of sacri fice. These results support the experimental data that cyto-toxic macrophages may occupy an important role in the defense against neoplasia. Furthermore, the application of xenogeneic activation of macrophages from tumor-bear ing animals rendering them cytotoxic may provide a possi ble approach to therapy.