Immune Responses Raised in an Experimental Colon Carcinoma Model Following Oral Administration of Lactobacillus casei

The role of dietary probiotic strains on host anti-cancer immune responses against experimental colon carcinoma was investigated. We have previously shown that Lactobacillus casei administration led to tumor growth suppression in an experimental colon cancer model. Here, we investigated the underlying immune mechanisms involved in this tumor-growth inhibitory effect. BALB/c mice received daily live lactobacilli per os prior to the establishment of a syngeneic subcutaneous CT26 tumor. Tumor volume, cytokine production, T cell differentiation and migration, as well as tumor cell apoptosis were examined to outline potential immunomodulatory effects following L. casei oral intake. Probiotic administration in mice resulted in a significant increase in interferon gamma (IFN-gamma), Granzyme B and chemokine production in the tumor tissue as well as enhanced CD8(+) T cell infiltration, accompanied by a suppression of tumor growth. Cytotoxic activity against cancer cells was enhanced in probiotic-fed compared to control mice, as evidenced by the elevation of apoptotic markers, such as cleaved caspase 3 and poly (ADP-ribose) polymerase 1 (PARP1), in tumor tissue. Oral administration of Lactobacillus casei induced potent Th1 immune responses and cytotoxic T cell infiltration in the tumor tissue of tumor-bearing mice, resulting in tumor growth inhibition. Thus, the microorganism may hold promise as a novel dietary immunoadjuvant in raising protective anti-cancer immune responses.