Immunopotentiation With BCG. IV. Factors Affecting the Magnitude of an Antitumor Response2

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Abstract
The immunopotentiating activity of BCG was studied in a test system that measured the capacity of irradiated murine tumor cells (mastocytoma, P815) to provoke systemic Immunity when injected into sites prepared by a prior injection of BCG; a tumor located remotely in the footpad was monitored for evidence of specific resistance. The time of onset and duration of immunity were established, and 3 variables affecting the degree of immunopotentiation were evaluated. The first sign of tumor inhibition occurred 7 days after the tumor-specific immunogenic stimulus was introduced, and maximum tumor immunity was achieved when the irradiated tumor cells were injected 10 days after the priming dose of BCG. The frequency of tumor suppression and overall survival rates were increased by raising the priming dose of BCG, but raising the dose of irradiated tumor cells beyond a certain optimum caused less suppression and lowersurvival rates. As previously observed, a significant level of antitumor immunity developed only when irradiated tumor cells were injected into BCG-infected sites; neither BCG nor irrad iated cells alone had any significant tumor-suppressive effect.

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