PDCD1 and metastatic melanoma: examined the stool samples collected from patients with metastatic melanoma before anti-PD-1 immunotherapy and found that Bifidobacterium longum, Collinsella aerofaciens, and Enterococcus faecium were more abundant in responders, indicating the antitumor effects of Bifidobacterium species in the context of PD-1 immunotherapy (80).