PDCD1 and melanoma: Clinical studies have shown that some of the bacterial species enhanced the efficacy of immune checkpoint therapy (48), such as the effect of Bacteroides caccae on anti-CTLA-4 and anti-PD-1 in melanoma (49), and the impact of A. muciniphila on anti-PD-1 in non-small-cell lung carcinoma (NSCLC) and renal cell carcinoma (RCC) (50).