CD81 and hepatocellular carcinoma: We observed that the abundances of CD9 and CD81 in the exosomes were significantly upregulated after overexpression of KLF4 or themselves in HCC cells, however, the upregulation of KLF4, CD9 or CD81 had no influence on CD63, Alix and TSG101 expression (Fig. 6d), implying that instead of affecting the total number of secreted exosomes, KLF4-CD9/CD81 signaling might change the subtypes of exosomes, which finally influenced the functions of HCC-derived exosomes.