Bifidobacterium Pseudocatenulatum W112 In Promoting Immune Checkpoint Blockade Therapy For Melanoma Gut Microbiota Can Be Modulated In The Treatment Of Melanoma

Melanoma is one of the most aggressive skin cancers.The incidence rate is increasing year by year,and the number of deaths of patients also occupies the overwhelming majority of the death cases in skin cancer.In recent years,immune checkpoint inhibition therapy has made great progress in tumor treatment,and has been widely used in the clinical treatment of solid tumors such as melanoma,renal cell carcinoma and non-small cell lung cancer.However,due to the difference of individual immunity,70%to 80%of patients can not respond well to immune checkpoint therapy.Therefore,it is of great significance to predict and develop methods to enhance the efficacy of immune checkpoint blocking.Recent studies on intestinal immunity and immune checkpoint therapy have shown that probiotic intervention of intestinal flora is a potential strategy to enhance the effect of immunotherapy for melanoma.Therefore,by constructing melanoma mouse model,this study evaluated the promoting effect of Bifidobacterium pseudocatenulatum W112 with antioxidant,regulating intestinal flora and promoting body immunity on immune checkpoint blocking therapy based on PD-1 antibody.By observing the appearance and tumor growth of mice,the therapeutic effect of W112 on melanoma with PD-1 antibody was preliminarily evaluated.The results showed that after treatment,compared with the weight of mice in tumor group(CON group)(24.32±0.32 g),the weight of mice in PD-1 antibody combined with w112 group(20.63±0.25 g)decreased significantly(P<0.05).The tumor volume of PD-1 antibody combined with W112 group(1198.67±3.42 mm~3)was significantly lower than that of tumor group(3291.17±5.25 mm~3)(P<0.01).After dissecting and weighing the tumor,the use of W112made the inhibition rate of PD-1 antibody to the tumor reach 72.39%,which was significantly higher than 67.74%when treated with PD-1 antibody alone.The promoting effect of w112 was further judged by measuring spleen index,thymus index,tumor tissue morphology and tumor immune microenvironment.The results showed that the spleen in untreated malignant tumor mice would appear swelling and edema,resulting in the increase of spleen index.The use of W112 can promote the remission of compensatory splenomegaly and edema during PD-1 antibody treatment.The use of W112can also promote the growth and development of thymus to a certain extent and improve the immunity of mice,so as to provide a more favorable immune environment for treatment.In addition,the study of tumor tissue morphology and immune microenvironment shows that compared with the tumor group,W112 can significantly improve the levels of IFN and IL-12 in tumor tissue during the treatment of melanoma with PD-1 antibody.At the same time,compared with the tumor group,the use of W112 made the tumor necrosis area larger and the tumor tissue more loose after PD-1 antibody treatment.Immunohistochemical staining showed that the area of CD8~+T cells in the tumor tissue treated with combination therapy(40%)was significantly higher than that in the tumor group(14%),which opened the gap between the positive cell score of tumor group(0)and that of combination therapy(3).Since intestinal flora is the main target of W112,the effect of W112 on the structure and function of intestinal flora in mice treated with PD-1 antibody was analyzed by metagenomic method.The results showed that after administration of W112,the immune related flora such as Firmicutes and Lactobacillus increased,and the relative abundance of Bacteroides,Proteobacteria,Bacteroides and alistipes decreased.The short chain fatty acids in mouse feces were determined by GC-MS.It was found that W112 promoted the production of short chain fatty acids during PD-1 treatment.Compared with the tumor group,W112 significantly(P<0.01)increased the contents of propionic acid and butyric acid,and significantly(P<0.05)increased the content of acetic acid.Correlation analysis showed that acetic acid,propionate and butyric acid were positive related to Firmicutes,Lactobacillus,tumor inhibition rate,survival rate,IFN-γ,IL-12 and CD8~+T cells,and negatively correlated with Bacteroides,Proteobacteria,Bacteroides and Alistipes.In conclusion,in this experiment,we found that Bifidobacterium pseudocatenulatum W112 can promote the tumor inhibition rate,prolong the survival rate of mice and reduce the tumor volume during the treatment of PD-1 antibody.The study confirmed that the promotion effect was mainly caused by the administration of W112,which changed the composition of intestinal flora of tumor mice,and then increased the microbial metabolite SCFAs content in mouse feces.The increased content of SCFAs in the intestine can affect the systemic immunity and tumor immune microenvironment of mice in many ways,thus promoting the therapeutic effect of PD-1 antibody.