Immunopotentiation with BCG: dimensions of a specific antitumor response

The dimensions of a BCG-potentiated antitumor response against the poorly immunogenic murine mastocytoma, P815 (MA), are described for a model in which the tumor immunogen is injected into subcutaneous sites previously infected with BCG; a distantly located tumor challenge is subsequently monitored for evidence of regression. A comparison of concomitant immunity and the immunity elicited by injection of varying doses of live MA into sites previously infected with BCG revealed similar antitumor effects. The subcutaneous site was the most effective route for immunization with BCG and irradiated tumor cells. Antitumor immunity was maximally expressed at intravascular sites and in the footpad. Complete tumor suppression was limited to footpadchallenge with 10-4-10-5 MA. Not only did the iv injection of BCG and immunogen fail to elicit immunity against subcutaneous challenge, but also systemically administered immunogens abrogated antitumor immunity elicited by subcutaneous immunization. These effects were reversed by prior splenectomy. Immunity was specific for the evoking tumor immunogen, but challenge with the specific tumor did not elicit nonspecific resistance against another 3-methylcholanthrene-induced tumor. In another strain of mice, immunity potentiated by BCG against the highly antigenic tumor, Meth A, was more effective than that potentiated against the poorly immunogenic MA.