Studies on metastases. I. Role of sensitization and immunosuppression.

A normally nonmetastatic tumor metastasized to the regional axillary lymph nodes following severe immunosuppression of inbred Swiss mice. The extent of metastasis was dependent on the severity of lymphocyte depletion and the initial number of tumor cells injected. Sensitization of the host to the tumor was important in prevention of metastasis: Metastasis was induced only if the immunosuppressive treatment occurred within 3 days of tumor inoculation. Antitumor immunity was adoptively transferred by the splenocytes from animals given immunosuppressive treatment with X-rays or hydrocortisone acetate on day 14. Though spleen cells from animals given both immunosuppressants did not have this property, that no metastasis was observed even in doubly immunosuppressed mice indicated sensitization to tumor cells. Lymphocyte number was important also: Injection of splenocytes from normal to tumor-bearing animals significantly reduced the occurrence of metastases.