Immunoprophylaxis of methylcholanthrene-induced tumors in mice with Bacillus Calmette-Guérin and methanol-extracted residue.

The immunoprophylactic effects of i.p. administration of Bacillus Calmette-Guérin (BCG) and methanol-extracted residue of BCG (MER) on the production of tumors by 3-methylcholanthrene (MCA) in C57BL/6 mice were investigated. At the dose level of MCA used (500 /ug i.m.), almost all mice developed tumors. Pretreatment of the mice with BCG either 2 weeks before or 2 weeks after carcinogen administration provided a significant temporary protection, demonstrated by a decreased rate of tumor appearance. Administration of MER at a 0.5-mg dose level conferred relatively little protection against tumor production. In those mice receiving 2.5 mg MER, either on the day of carcinogen administration or both at that time and when the first experimental tumor was found, significant temporary protection against MCA carcinogenesis was obtained. This was demonstrated by a lengthened latent period before tumor production, although subsequently the rate of tumor production was similar to that of the controls. It is concluded that BCG and MER are capable of affecting the induction of MCA-induced tumors.