Host-mediated antitumor activity of Lactobacillus casei in mice

Antitumor activity of Lactobacillus casei YIT 9018 ( LC9018 ) was studied in BALB/c mice by using two syngeneic tumors; methylcholanthrene-induced tumor (Meth A fibrosarcoma) and Kirstein murine sarcoma virus-transformed BALB/3T3 ( K234 tumor). Administration of an LC9018 -Meth A cell mixture induced complete suppression of the tumor growth, while simultaneous injections of LC9018 and Meth A cells into different sites had no suppressive effect on the tumor growth. Administration of the mixture subsequently induced specific transplantation immunity to the challenge tumor, which started to be generated on about the 5th day after the administration and continued to at least the 30th day. Administration of an LC9018 - K234 cell mixture also induced suppression of the tumor growth and generated specific antitumor immunity. Neutralization (Winn type) tests showed that T lymphocytes possessed tumor cytotoxicity but humoral immune serum did not, suggesting that the T cells with LC9018 -potentiated antitumor immunity functioned in the suppression of the tumor growth.