Antitumor activity of bacterial infection. II. Effect of Listeria monocytogenes on growth of a guinea pig hepatoma

Growth of a guinea pig hepatoma was suppressed when tumor cells were mixed with viable Listeria monocytogenes (LM) before intradermal (ID) injection into syngeneic recipients. Heat killed LM were less effective than viable organisms in suppressing tumor growth. A vaccine containing oil droplets and LM cell walls lacked antitumor activity. Intratumor injection of viable LM on the 7th day after ID injection of tumor cells prolonged survival of guinea pigs that did not succumb to LM injection. After intratumor injection of 0.6 x 10 ⁸ to 1.0 x 10 ⁸ LM, 5 of 22 guinea pigs died from acute infection (23%). In the 17 survivors, 3 tumors regressed completely (18%). Animals surviving injections of LM and tumor cells were immune to a second challenge with tumor cells. Immunization of guinea pigs with an intravenous injection of LM decreased the mortality from intratumor injection of LM, but the intratumor injection of LM failed to cure a significant fraction of LM immune animals bearing 7 day hepatoma transplants. BCG was more effective than LM in producing tumor regression. Synergism between LM and BCG was not observed, and simultaneous intratumor injection of BCG and LM was no more effective than intratumor injection of BCG alone in the treatment of 12 day tumor transplants.