Rifampicin-induced suppression of antitumor immunity.

The effect of rifampicin on transplantable tumor growth and antitumor immunity was studied. The growth of transplantable lung sarcoma was significantly enhanced in mice when rifampicin was given for 7 days or longer. Also, the antitumor effects of preimmunization of the animals with killed tumor cells were abrogated by this antibiotic. In vitro studies showed that spleen cells from tumor-bearing animals expressed significantly lower specific cytotoxicity toward syngeneic tumor cells, when the animals had been previously treated with rifampicin. Also, natural killer activity in healthy animals was diminished in mice receiving the antibiotic.