Tumour metastasis in mice with reduced immune reactivity. III. Studies with three weakly antigenic tumours in thymectomized and/or sub-lethally irradiated mice.
A previous observation that increased spontaneous metastasis formation from the highly antigenic MCA-induced sarcoma MCG101 occurred in immunosuppressed C57BL/6J mice prompted the present study to establish whether or not tumours capable of inducing only weak transplantation resistance would behave similarly. One MCA-induced sarcoma, MCG12, one epidermoid carcinoma, EpCa1 in CBA mice and a spontaneous mammary carcinoma, MaCa1 in C3H mice, were transplanted into adult thymectomized and/or sub-lethally irradiated mice at different intervals after irradiation. The effects of the treatments on the immunoreactivity were monitored in separate groups by determining the primary and secondary responses to SRBC and the survival of first set allogeneic skin grafts. The treatment resulted in a significantly increased incidence of mainly the lymph-node metastases with MCG12 and of only the lung metastases with EpCa1. No increase in metastases was noted with MaCa1. Thymectomy potentiated the increase in metastases from MCG12 in irradiated mice but unexpectedly so only for a limited time after irradiation. Local growth of MCG12 and MaCa1 at the transplantation site was more rapid in females than in males. The changes in tumour growth and spread induced by the treatments varied with tumour-host system, sex and time of transplantation after irradiation and did not conform well with any of the tested parameters of immunoreactivity. There was no close parallel between the effects of the treatments on growth and spread of the tumours.