Combined Extract of Heated 4T1 and a Heat- Killed Preparation of Lactobacillus Casei in a Mouse Model of Breast Cancer

Background: The adjuvanticity potential of Lactobacillus casei was first suggested in an old survey. The present study was designed to investigate the efficacy of a new immunotherapy against breast cancer made by mixing an extract of heated 4T1 mammary carcinoma cell line and a heat-killed preparation of Lactobacillus casei. Methods: Female BALB/c mice (6–8 weeks old, n=40) were challenged subcutaneously in the right flanks with 4T1 cells. When all the animals developed a palpable tumor, they were allocated to 4 equal groups and immunotherapy was initiated. The tumor-bearing mice in the experimental groups received the extract of heated 4T1 or heated Lactobacillus casei and/or a combination of both, twice at a 1-week interval. The mice in the control group received phosphate-buffered saline. One week after the last immunotherapy, one half of the mice were euthanized to determine the immune response profile. The remaining animals were kept until death occurred spontaneously. Results: The animals receiving the combined treatment significantly showed more favorable survival curves and slower rates of tumor development than the tumor-bearing mice receiving only the heated 4T1 and/or the negative control mice. The combined immunization significantly amplified the production of nitric oxide and the cytotoxicity of natural killer cells in the spleen cell culture of the tumor-bearing mice. Moreover, the combined immunotherapy significantly increased the secretion of IFN-γ and conversely diminished the secretion of IL-4 and TGF-β in the splenocyte population compared to the splenocytes from the other groups. Conclusion: The combined immunotherapy with heated 4T1 cells and heated Lactobacillus casei conferred beneficial outcomes in our mouse model of breast cancer.