PDCD1 and metastatic melanoma: Matson et al., assessed the relationship between commensal microbiome composition and clinical response to ICIs in metastatic melanoma patients and found greater efficacy for anti-PD-1 immunotherapy in patients (n = 16) with a higher abundance of Bifidobacterium longum, Collinsella aerofaciens, and Enterococcus faecium, compared to a higher relative abundance of Ruminococcus obeum and Roseburia intestinalis in non-responders (n = 26) [18].