LATENT MEMBRANE PROTEIN 2A (LMP2A) MIMICS B‐CELL RECEPTOR SIGNALING AND PROMOTES IMMUNE ESCAPE IN EPSTEIN‐BARR VIRUS (EBV)‐POSITIVE DIFFUSE LARGE B‐CELL LYMPHOMA (DLBCL)

Abstract

Background: EBV+ DLBCL is an aggressive malignancy that is largely resistant to current therapeutic regimens. LMP2A is expressed during different latency stages of EBV-infected B cells in which it triggers activation of cytoplasmic protein tyrosine kinases. Early studies have revealed that an immunoreceptor tyrosine-based activation motif in the cytoplasmic N-terminus of LMP2A can trigger a transient increase of the cytosolic Ca2+ concentration similar to that observed in activated B cells. Meanwhile, tumor cells often express PD-L1 in EBV+ DLBCL, providing a possible mechanism for immune escape. We thus explored the correlations between LMP2A expression, B-cell receptor (BCR) signaling, and PD-L1 expression in EBV+ DLBCL. Design: Two cohorts of DLBCL cases, respectively EBV-positive (n=28) and EBV-negative (n=32), were selected. LMP2A, PD-L1 and the BCR signaling-related molecule, phosphorylated form of SYK (pSYK), were immunohistochemically evaluated on formalin-fixed, paraffin-embedded tumor tissues. The expression status of LMP2A, pSYK and BCR were further validated by a flow cytometry analysis using fresh tissues from 3 EBV-positive and 5 EBV-negative DLBCL patients. Results: The EBV-positive cases, with a median age of 61yrs, were more frequently associated with a high-risk IPI score and a non-GCB phenotype (P=0.029). Compared with EBV-negative ones, patients with EBV-positive tumors showed a worse response to the RCHOP therapy and a shorter median survival (P = 0.041). Twenty-one EBV-positive cases (75 %) expressed LMP2A, whereas none of the EBV-negative cohort expressed this protein. The expression level of pSYK was significantly lower (P = 0.0313) in EBV+ DLBCL cases than those EBV-negative ones, and the pSYK level correlated negatively with LMP2A level (P = 0.119). The expression level of PD-L1 was significantly higher (P = 0.042) in EBV+ DLBCL, which correlated positively with the LMP2A level (P=0.184). Flow cytometry confirmed the LMP2A expression in EBV+ DLBCL, which correlated with a down-regulated BCR and pSYK expression. Conclusions: EBV+ DLBCL seems to feature an inactive BCR signaling, which may be related to the expression of LMP2A. Besides, LMP2A may function and promote the PD-L1 expression. These findings indicate that targeting immune checkpoints including PD-1/PD-L1 instead of BCR signaling molecules seems to be more reasonable and promising for the treatment of EBV+ DLBCL. Keywords: diffuse large B-cell lymphoma (DLBCL); Epstein-Barr virus (EBV).