[Augmentation of antitumor immune responses by the antitumor antibiotic bleomycin]

We investigated the augmentation of antitumor immune responses by the antitumor antibiotic, bleomycin (BLM). BLM augmented immune responses against tumor cells, such as transplantation resistance and tumor cell-neutralizing activity of spleen cells, in rats immunized with the tumor cells or bearing the tumor as a result of selective elimination of immune-suppressor cell activities. Moreover, BLM was able to activate macrophages as an effector of antitumor resistance. We observed good correlation between the therapeutic effects of BLM and the above immune augmentation when tumor-bearing rats were treated with the drug. These results suggest that the chemotherapeutic action of BLM partially depends on a host-mediated effect, i.e., antitumor immune responses augmented by the drug.