Enhanced development of metastatic foci in thymectomized, irradiated, and bone marrow-reconstituted mice.

The effect of depletion of immunocompetence of metastasis of a mouse hepatoma MH-134 was studied in syngeneic C3H/He mice. (2) Development of metastasis in the lung and lymph nodes was remarkably enhanced in the mice which were thymectomized, irradiated, bone marrow-reconstituted (Tx-X-BM), and grafted intramuscularly with tumor cells. (2) Number of tumor cells detected in the blood stream was within the same range in the control mice and the Tx-X-BM mice after intramuscular tumor-grafting. (3) Metastatic foci were not detected in the stomach and intestines, not only in control mice but also in the Tx-X-BM mice after intramuscular tumor-grafting. However, tumors grew progressively in the subserosal tissues of these organs of the Tx-X-BM mice, but not of the control mice, when a small number of tumor cells were directly inoculated into such tissues. (4) On 9th day after an intravenous injection of a large number of tumor cells, tumor growth was detected to almost the same extent in the lungs of the control mice and the Tx-X-BM mice. Tumors grew progressively in the Tx-X-BM mice thereafter, whereas the tumors regressed in the control mice. These results suggest that inhibition of metastasis by immune response depends primarily upon suppression of proliferation of the tumor cells lodged in individual organs.