PDCD1 and neoplasm: It has also been shown that intestinal microorganisms can play an antitumor role by regulating innate immunity and acquired immunity [12], and it has also been found that Bifidobacterium can increase the antitumor effect of CD8+T cells in tumor tissue through dendritic cells and enhance the antitumor effect of PD-1 and CTLA-4 molecular-targeted drugs [13].