Immunotherapy of primary methylcholanthrene-induced mouse tumours by intratumoral BCG

Tumours were induced s.c. in C3H/uip, SJL/uip, DBA/2 uip, C57BL/6 uip and BDF1 mice by different doses of methylcholanthrene (MCA) diluted in oil: 1 mg, 0.1 mg and 0.01 mg. In each mouse strain, tumour frequency showed a different decreasing pattern in relation to the decreasing dose of MCA. Tumour latent period (LP) increased between the 1mg and 0.1mg doses of MCA, but the 0.01mg dose induced tumours with a similar or shorter LP than those tumours induced by 1 mg. Half of the tumours were treated with two injections of intratumoral (IT) BCG. The strains of mice differed in their sensitivity to this treatment, but only tumours induced by 0.01 mg MCA were sensitive to IT BCG. The induction of tumours by MCA pellets gave similar results. After transplantation of the untreated tumours, very few were cured by BCG treatment. Analysis of the role of tumour LP, growth rate and immunogenicity favours a slow growth rate as the most important characteristic for BCG sensitivity of the primary tumour. The tumours induced by 0.01 mg MCA were less immunogenic than those induced by 1 mg MCA, but the difference was not significant. This finding permits us to exclude an important role for tumour immunogenicity in the sensitivity of the primary tumour to BCB.