CD274 and hepatocellular carcinoma: In hepatocellular carcinoma under hypoxic conditions, circPRDM4 acts as a scaffold to recruit HIF-1α to the CD274 promoter and consolidates their interaction, ultimately facilitating HIF- 1α-mediated transactivation of PD-L1 while inhibiting CD8 + T-cell infiltration into the tumor microenvironment and promoting immune escape [83] (Table 3).