PDCD1 and melanoma: In a recent prospective study of patients with advanced melanoma who were treated with a combination of anti-PD-1 and anti-CTLA-4 ICIs, the profiling of gut microbiota demonstrated a significantly higher pre-treatment fecal abundance of Bacteroides intestinalis in patients with any ≥ grade 3 toxicities, which correlated with upregulation of mucosal IL-1β in biopsy samples and a more diverse peripheral T cell repertoire (105).