Application of combination of bacteroides fragilis capsular polysaccharide A and immune checkpoint inhibitor in preparation of drugs for treating digestive system tumors

According to the application of the combination of the bacteroides fragilis capsular polysaccharide A and an immune checkpoint inhibitor in preparation of drugs for treating digestive system tumors, the bacteroides fragilis capsular polysaccharide is the capsular polysaccharide A extracted from bacteroides fragilis ZY-312 by using the method disclosed by the invention, the relative molecular weight is 70-90kda, and the content of combined lipid is lower than 0.02% or the bacteroides fragilis capsular polysaccharide A does not contain lipid. The bacteroides fragilis capsular polysaccharide A is used as a main active component to be prepared into biological preparations such as a pharmaceutical preparation and a pharmaceutical composition, and is combined with an immune checkpoint inhibitor to treat digestive system tumors, so that the response rate and the treatment effect of the immune checkpoint inhibitor can be increased, and side effects are reduced. 脆弱拟杆菌荚膜多糖A与免疫检查点抑制剂联用在制备治疗消化系统肿瘤药物中的应用，其中，所述脆弱拟杆菌荚膜多糖为使用