Inhibition and promotion of tumor growth by BCG: Evidence for stimulation of humoral enhancing factors by BCG

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Abstract
Effects of pretreatment with BCG, strain Japan, on tumor growth were studied using a transplantable methylcholanthrene (MCA)-induced fibro-sarcoma in C3H/He mice. Injection of BCG 7 weeks before tumor inoculation at a site distant from the tumor caused a slight inhibition of tumor growth. A low dose of tumor cells did not grow at the BCG-primed site when BCG was injected 7 and 11 weeks before the tumor. When a high dose was inoculated into the BCG-primed site, inhibition of the primary tumor occurred in mice which had received BCG 7 weeks previously, but the number of distant metastases in the popliteal lymph node and the lungs was increased in mice pretreated with BCG at any time. Furthermore, post treatment with BCG at a site distant from the tumor caused promotion of tumor growth. Enhanced antibody formation and suppression of delayed type hypersensitivity(DTH) occurred in tumor-bearing mice. BCG treatment of such mice caused a vigorously enhanced antibody formation and a marked suppression of DTH. The sera from tumor-bearing mice enhanced tumor growth. Tumor growth was suppressed in splenectomized mice. These findings suggested that antibodies against tumor-specific antigens enhanced tumor growth in this system and that BCG treatment of tumor-bearing mice stimulated formation of antibodies probably acting as blocking factors.