Immunotherapeutic and Immunoprophylactic Effects of BCG on 3-Methylcholanthrene-Induced Autochthonous Tumors in Swiss Mice23

The immunoprophylactic effects of BCG on the development of tumors by 3-methylcholanthrene (MCA) in SWM/Ms mice were investigated. During the observation period (35 wk after MCA injection), more than 80% of control mice developed tumors. Intradermal injection with BCG 2 weeks before MCA administration significantly decreased tumor incidence; administration ot BCGat the time mice were beginning to produce palpable tumors was ineffective. The immunotherapeutic effects of BCG on the autochthonous tumors were also studied in the tumors induced by MCA. BCG was injected directly into the tumors when a tumor grew more than 5 mm in diameter. Although control tumors without BCG developed progressively and killed the hosts, intratumor injection with BCG showed therapeutic effects on about 50% of the tumors. The fate of tumors after BCG injection varied; they showed either regression and cure, regression and relapse, retardation, or progression. Results of experiments with intratumor injection with BCG on K3 and K5 syngeneic tumors suggest growth rate and/or antigenicity of individual tumor are important in influencing the therapeutic effects of BCG.