Chen et al. discovered that programmed death-ligand 1 (PD-L1), which acts in concert with programmed cell death protein 1 (PD-1) to suppress the antitumor immune response, was enriched in cancer-derived EVs and thus proposed the use of exosomal PD-L1 as a novel predictive biomarker for anti-PD-1 therapy [78]. The gene discussed is PDCD1; the disease is cancer.