Effects of oral administration of Lactobacillus casei on antitumor responses induced by tumor resection in mice.

The effects of an oral administration of BLP, a preparation of viable Lactobacillus casei YIT 9018, upon tumor growth and the mitogenic responses of splenocytes from tumor-bearing mice were studied. BALB/c mice were insufficiently pre-immunized by resecting a Colon 26 tumor mass (primary tumor) grown for 5 days intradermally. Thereafter, mice were rechallenged by injecting Colon 26 tumor (secondary tumor) into the hind footpad. The secondary tumor grew progressively in control mice, but was markedly suppressed by oral administration with BLP at a dose of 100 or 200 mg/kg/day for 7 consecutive days. The suppression was a primary tumor-specific response. Viable L. casei, not heat-killed L. casei, could suppress the secondary tumor. Although the lymphoproliferative responses of splenocytes from the secondary tumor-bearing mice with T-cell mitogens (concanavalin A and phytohaemagglutinin) and cytokines (interleukin-1 and interleukin-2) were lower than those of normal mice, this suppression of mitogenic responses under tumor-bearing conditions was abolished by oral administration with BLP. Thus we concluded that oral BLP potentiated systemic immune responses that modified T-cell functions in tumor-bearing mice.