CD9 and hepatocellular carcinoma: In order to clarify whether exosome secretion influences the abundance of PD-L1 in HCC cells, Rab27a30, mediating exosomes release, was knocked down, which significantly inhibited the secretion of exosomes as measured by exosomes markers, ALIX, TSG101, CD63, and CD9, or the total amount of exosomal protein (Fig. 4h and Supplementary Fig. S4d).