Abstract
Recent advances in immunotherapy, as a part of the multidisciplinary therapy, has gradually gained more attention. However, only a small proportion of patients who sensitive to the therapy could gain benefits. An increasing number of studies indicate that intestinal microbiota could enhance the efficiency of cancer immunotherapy. As one of the main probiotics, Bifidobacterium plays an important role in immune regulation, which has been proved by animal research and human clinical study. But the detailed mechanism was not clearly elucidated. Here we found oral administration of Bifidobacterium breve (B. breve) lw01 could significantly inhibit tumor growth and up-regulate tumor cell apoptosis, which relied on the recruitment of tumor-infiltrating lymphocytes and dendritic cells (DCs) in tumor microenvironment, but not Lactobacillus rhamnosus (L. rhamnosus) CGMCC 1.3724 or Escherichia coli (E. coli) MG1655. In the in situ ligated intestine loop model, B. breve's stimulation triggered the upregulated expression of DC-related chemokine CCL20 and recruited more DCs in the intestinal villi. Further study revealed the enhancement of interleukin 12 (IL-12) secretion derived from DCs is essential to B. breve's antitumor effect, which was counteracted by the treatment of neutralizing antibody for IL-12. Meanwhile, the modulation of intestinal microbiota caused by exogenous B. breve might enhance its antitumor effect. This study provides a simple and easy way to promote antitumor immunity via B. breve.