Tumour metastasis in mice with reduced immune reactivity. IV. Restoration of relative resistance to metastasis formation in thymectomized sub-lethally irradiated mice by spleen cells.

Adult thymectomy and/or sub-lethal irradiation increased spontaneous metastasis formation in several syngeneic murine systems (MCA-induced sarcomas MCG101 in C57BL/6J mice, MCG12 in CBA mice and MCA-induced epidermoid carcinoma EpCa1 in CBA mice). In order to differentiate between immunological and non-immunological effects of these treatments on tumour spread the effects of presumed selective restoration of immune competence by transfer of syngeneic spleen cells from normal donors shortly after irradiation (1.5 months before tumour transplantation) was perfomed. This procedure brought the resistance of thymectomized irradiated mice to tumour spread back to the level seen in untreated mice, providing further evidence for the conclusion that the indrease of tumour spread in this experimental model to a major part was immune-mediated. In thymectomized irradiated mice adoptive transfer of concomitant immunity by spleen cells from tumour-bearing mice soon after tumour transplantation completely inhibited the spread of the highly antigenic MCG101 and reduced that of the weakly antigenic MCG12 to control level. In contrast, adoptive transfer after tumour resection had no significant effect of the spread from either to the tumours.