Current studies on the function of exosomal PD-L1 derived from melanoma [5], gastric cancer [31], non-small cell lung cancer [32,33], osteosarcoma [34], and other tumors have demonstrated that exosomal PD-L1 could inhibit T cell activity and accelerate tumor growth through interaction with PD-1 in vitro. Here, PDCD1 is linked to melanoma.