Research has found that Lactobacillus johnsonii and Clostridium sporogenes in the intestinal commensal microbiome work synergistically to produce the tryptophan metabolite indole‐3‐propionic acid (IPA), which can significantly promote CD8+ T cell infiltration into tumor tissues, thereby enhancing the efficacy of anti‐PD‐1 immunotherapy [124]. Here, PDCD1 is linked to neoplasm.