The Mechanism Of Tumor Growth Inhibition Derived From Oral Administration Of Bifidobacterium Breve

Background and objective:Recent advances in immunotherapy,as a part of the multidisciplinary therapy,has gradually gained more attention.However,only a small proportion of patients who are sensitive to the therapy can 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.In this study,we used the murine squamous cell carcinoma cell line SCC ?,which possesses low immunogenicity,to establish the transplanted subcutaneous tumor model in C3H/HeN mice.We evaluated the efficacy and explored detailed mechanisms of Bifidobacterium breve(B.breve)on subcutaneous tumors in mice by oral administration.Methods:The murine squamous cell carcinoma cell line SCC ? was used to establish the transplanted subcutaneous tumor model in C3H/HeN mice.The mice were randomly grouped and fed with B.breve,Lactobacillus rhamnosus(L.rhamnosus),Escherichia coli(E.coli)or PBS.The tumor volume was monitored every other day.TUNEL staining and western blotting were used to detect tumor apoptosis;immunohistochemical staining and flow cytometry were used to detect tumor infiltrating T cells;immunohistochemical staining was used to detect interleukin 12(IL-12)and interferon-?(IFN-?).Ligated intestinal loop experiments was used to explore the recruitment of intestinal dendritic cells(DCs)and the expression of IL-12 after the treatment by the three kinds of bacteria.Bone marrow-derived DCs(BMDCs)were cultured in vitro,and were used to analyze related gene expression and the secretion of IL-12 after bacteria stimulation.Murine IL-12 neutralizing antibody was used to verify the key role of IL-12 in the antitumor effect.The 16S rRNA gene sequencing of intestinal contents was also conducted to analyze changes of intestinal microbiota.Results:Orally taken B.breve could significantly up-regulate tumor cell apoptosis and inhibit tumor growth.Tumor infiltrating T cells were significantly increased,and expression of IFN-? and IL-12 were up-regulated in tumor microenvironment.After B.breve stimulation in ileum ligation loop,the expression of DC-related chemokine CCL20 was up-regulated,and more CD103-CDllb+DCs were recruited in the intestinal villi.However,L.rhamnosus and E.coli didn't possess such effects.In vitro both of B.breve and E.coli could induce the maturation and activation of BMDCs,and the expression and secretion of IL-12.IL-12 neutralizing antibody could completely counteract the effects of orally taken B.breve in promoting T cell tumor infiltration and tumor cell apoptosis,and inhibiting the growth of subcutaneous tumors in mice.B.breve could colonize in the intestine after gavage,and increase the species abundance of the intestinal microbota and change the microbiota composition.Conclusion:Orally administrated B.breve can induce tumor cell apoptosis and inhibit the growth of subcutaneous tumors in mice.The mechanism is that B.breve up-regulates the expression of chemokine CCL20 in the intestinal epithelium and recruits more DCs.Then the expression and secretion of IL-12 promote the infiltration of T cells into the tumor microenvironment.In addition,the changes of the microbiota composition and the increase of species diversity may provide beneficial effect to anti-tumor immunity.