The effect of syngeneic tumor cell mixed with BCG on intradermal tumor growth and on specific tumor immunity was evaluated. (1) With the use of several early transplant generations of syngeneic mouse tumors, the ratio of 1:10 to 1:20 of tumor cell--BCG was confirmed as the best for the present mouse--tumor system. (2) The development of immunity capable of eradicating distant tumor deposit was tested by varying doses of tumor deposit inoculated at the same time as the mixture of tumor cell--BCG. The remarkable efficacy of the tumor cell-BCG mixture on local tumor suppression (7/8) and tumor immunity (5/7) was proved with tumor burden of 10(5) cells or less. Control mice receiving BCG contralateral to the tumor site (10(5)) were not able to achieve tumor immunity (1/8), but were able to reject the local tumor (8/8). (3) The tumor cell--BCG mixture was as effective in a line of rat lung carcinoma as it was in the mouse system in rejecting both the local tumor and the tumor challenge injected intramuscularly. (4) Intratumor injection of BCG or nonliving BCG preparation (in which whole cell wall of BCG is attached to oil droplets) in primary tumors in mice previously sensitized with BCG led to a few instances of complete tumor regression in animals having tumor nodules of 3 to 10 mm in diameter. The survival period of animals treated with BCG or with nonliving BCG preparation was significantly longer than that of saline-treated controls.
