Targeting the ANXA2-CD63-exosomal PD-L1 axis in hepatocellular carcinoma: A novel mechanism of immune evasion and its implications for precision immunotherapy.

BACKGROUND AND PURPOSE: Hepatocellular carcinoma (HCC) remains one of the leading causes of cancer-related deaths globally due to late diagnosis and resistance to therapies, including immune checkpoint blockade (ICB). Tumor-derived exosomes carrying programmed death-ligand 1 (PD-L1) have emerged as key mediators of immune evasion by binding PD-1 on T cells, thereby inducing T cell exhaustion and systemic immunosuppression. This study investigated whether Annexin A2 (ANXA2) modulates exosomal PD-L1 expression in HCC cells to inhibit T-cell function and promote immune escape. RESULTS: Bioinformatic analyses (TIMER2.0, TCGA) showed ANXA2 upregulation in HCC, correlating with fewer CD8⁺ T cells and poor survival. ANXA2 knockout (KO) in Hepa1-6 cells reduced exosome secretion and exosomal PD-L1, confirmed by EM, nanoparticle tracking, and WB. Exosomes from controls suppressed CD8⁺ T cell activation (reducing CD69, IL-2, IFN-γ, TNF-α), while KO exosomes did not. ANXA2 KO tumors grew slower in immunocompetent C57BL/6 J mice but not in immunodeficient BALB/c Nude mice, highlighting immune dependence. ANXA2 depletion reduced CD63 protein stability without affecting mRNA. CD63 re-expression in KO cells restored exosomal PD-L1, indicating ANXA2 maintains CD63 stability for PD-L1 exosomal incorporation. Transcriptomic and pharmacologic evidence further supported a role for lysosome-associated turnover in CD63 loss upon ANXA2 depletion. CONCLUSIONS: ANXA2 drives HCC immune evasion by upregulating exosomal PD-L1 via CD63 stabilization, offering a novel target to enhance ICB efficacy. This work highlights a tumor-specific exosome regulation mechanism, with potential implications for immunotherapy across exosome-dependent cancers.