Dose-dependent adjuvant effects of Bacillus Calmette-Guérin on tumor immunity in Lewis rats.

The study was undertaken of the ability of Bacillus Calmette-Guérin (BCG), used in combination with a live tumor cell vaccine, to potentiate systemic antitumor immunity in rats. BCG was administered in two injections, with the first one given i.v. and the second one given intradermally mixed with the tumor cell vaccine 12 days later at the time of implant of an s.c. tumor, which served to monitor antitumor immunity. Both these BCG injections were necessary to obtain maximal protection measured in terms of increased survival rates of the rats and of decreased tumor growth rates. The dose of BCG in both the first and second injections was critical for optimal protection, since low doses (125 to 250 micrograms) afforded protection, while higher doses (over 1500 micrograms) decreased or abolished the protective effect. These results strongly suggest that BCG, only if administered under the appropriate conditions, is able to potentiate systemic tumor immunity and to provide a significant level of protection for a tumor-bearing animal.