The treatment of established micrometastases with syngeneic macrophages

We demonstrated that macrophages injected systemically can profoundly inhibit the incidence of experimentally induced metasis. In our system mice bearing established micro-metastases were treated with one, two, or three i.v. injections of activated macrophages. Specificially activated (immune) macrophages were most efficient in reducing the number of metastases, but non-specifically activated macrophages were also effective in reducing the metastatic incidence. Macrophage play a major role in host defense against neoplasia (9,22) and have been shown to influence the outcome of spontaneous metastasis (9). Rat sarcomas whose macrophage content was found to be high were also shown to be non-metastatic. Conversly, rat sarcomas with low macrophage content were found to be metastatic (9). Our current data demonstrate that the systemic injection of syngeneic activated (exogenous) macrophages can bring about a significant reduction of lethal cancer metastases. Apparently, treatment with activated macrophages can increase the rate of tumor cell destruction as compared to the rate of tumor cell proliferation which ultimately leads to inhibition of clinical metastasis.