Epstein-Barr virus (EBV)-positive diffuse large B-cell lymphoma (DLBCL) is a highly aggressive malignancy with inferior outcomes after treatment, which might be largely attributed to the immune escape induced by EBV via modulation of the immune checkpoint programmed cell death 1 (PD-1)/PD-ligand 1 (PD-L1). This study aimed to explore the role that EBV-encoded latent membrane protein 2A (LMP2A) played in the mechanisms of immune escape of EBV+ DLBCL cells. Ten cases each of EBV+ DLBCL with and without immunohistochemical expression of LMP2A were submitted for evaluation of PD-L1, p65/nuclear factor-κB (NF-κB), phosphorylated SYK (pSYK), and p-p65 expression by immunohistochemistry. To observe the relationship between LMP2A expression and the tumor immune microenvironment, tumor-infiltrating CD4+ and CD8+ T-cell levels were also evaluated by immunofluorescence assay. Compared with LMP2A- cases, LMP2A+ cases exhibited more pronounced biologic aggressiveness and featured a significantly higher level of pSYK, p-p65, and PD-L1 and increased CD4+/CD8+ ratio. In vitro experiments were conducted to ascertain the effects of SYK and p65/NF-kB signaling on PD-L1 expression in the OCI-LY8 cells. After transfection with LMP2A, the expression levels of pSYK, p65, p-p65, and PD-L1 were all elevated, and knockdown of p65 or pSYK in LMP2A-transfected DLBCL cells resulted in PD-L1 inhibition. Our work indicates that LMP2A may mimic B-cell receptor and trigger the SYK/NF-κB signaling, which subsequently influences the PD-L1 levels of tumor cells and the tumor immune microenvironment, thus facilitating the immune evasion of lymphoma cells. These findings may have clinical implications for modulating or improving the therapeutic strategies of patients with EBV+ DLBCL.
Keywords: Epstein-Barr virus; diffuse large B-cell lymphoma; immune escape; latent membrane protein 2A; nuclear factor-κB; programmed cell death ligand 1.
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