PDCD1 and melanoma: Emerging evidence shows that exosomes secreted by tumor cells have bioactive PD-L1 on their surface, which can suppress the immune response.350–354 Based on the clinical data of patients with melanoma or NSCLC,351,355 exosome-derived PD-L1 in response to treatment with anti-PD-1/PD-L1 antibodies (e.g., nivolumab and pembrolizumab) may have the potential to predict the clinical outcomes of anti-PD-1 therapy, or even to become a novel therapeutic target, in spite of the ambiguity of the relationship between EMT and PD-L1 levels within exosomes.