Melanoma patients who responded to anti-PD-1 therapy had a higher diversity of bacteria and a higher abundance of RuminococcaceaeGerm-free mice transplanted with stool samples from patients responded to anti-PD-1 and anti-PD-L1 therapy had a significantly reduced tumor growth and improved responses to anti-PD-1 and anti-PD-L1 therapy coupled with higher density of CD8+ T cells in tumor. Here, CD8A is linked to melanoma.