[Current topics on tumor immunology].

The historical review of the immune surveillance was briefly mentioned. From the standpoint of tumor antigens, it was stressed that the potent antigenicity of tumor cells is primarily of importance in cancer immunotherapy. As for the augmentation of the antigenicity of tumor cells, highly immunogenic tumor hybrid cells were prepared by cell fusion between syngeneic cultured fibroblasts and primary methylcholanthrene-induced fibrosarcoma cells. The hybrid cells inoculated induced the immunity in syngeneic hosts against the challenging parent tumor cells, but enhanced humoral immune response pre-existed in tumor-bearing state, resulting in tumor-growth enhancement. The suppression of humoral response by administration of cyclophosphamide and following injection of the immunogenic hybrid cells or spleen cells of mice immunized with the hybrid cells could eliminate tumor effectively. Thus, the efficacy of active cancer immunotherapy will be achieved only after suppression of the tumor escape mechanism.