To further confirm that the PD-L1 in exosomes was from cancer cells but not from other components, exosome secretion inhibitor GW4869 was used to inhibit the secretion of extracellular vesicles, and there was an obvious reduction of exosomal secretion when exosomes were purified from the same number of cells (Supplementary Fig. 4a) and significant accumulation of membrane PD-L1 (Supplementary Fig. 4b) as well as total PD-L1 (Supplementary Fig. 4c) was observed when BGC-823 cells were exposed to GW4869. The gene discussed is CD274; the disease is cancer.