[5] disclosed that the particular gut microbiota profiling, such as Bifidobacterium longum, Enterococcus faecium, and Collinsella aerofaciens, was crucially enriched in the responders to PD-1 blockade therapy among metastatic melanoma patients, whose fecal material unexpectedly induced the effects of curbing tumor growth, enhancing T cell response, and maintaining anti-PD-1 therapy in germ-free mice with melanoma. This evidence concerns the gene PDCD1 and metastatic melanoma.