Bifidobacterium alleviates the symptoms of anti-CTLA-4 ICI-induced colitis in melanoma-afflicted mice.249 Gopalakrishnan et al.250 found the gut microbiome modulates a response to anti-PD-1 immunotherapy in melanoma patients through enhancing antigen presentation or increasing T cell recruitment to the TME. Here, PDCD1 is linked to melanoma.