[Modification of suppressor activity and effector activity of tumor-bearing hosts by bleomycin]

We investigated the immunological role of an antitumor antibiotic, bleomycin (BLM) in its therapeutic effects. BLM was found to be one of unique antitumor agents which can augment the antitumor immune responses in the tumor-bearing hosts. The evidence was provided by the following experimental results. The therapeutic effect of BLM on a transplanted rat tumor is host-mediated and administration timing-dependent. BLM eliminates suppressor cell activity induced in tumor-bearing rats and augments tumor-neutralizing activity and responsiveness of spleen cells to tumor associated antigen. BLM also activates tumoricidal activity of peritoneal macrophages of rats. Thus, it is suggested that the antitumor immune response augmented by BLM plays an important role in the therapeutic effects of BLM.