Epstein-Barr virus LMP1 enhances levels of large extracellular vesicle-associated PD-L1

Abstract

ABSTRACT The circulating nature of extracellular vesicles (EVs) allows for the transfer of cargo to proximal or distant cells, making them vital mediators of cellular communication. Epstein-Barr virus (EBV)–infected cells have been found to release EVs containing viral proteins, such as the major viral oncogene latent membrane protein 1 (LMP1). LMP1 has been observed to regulate the cellular gene expression of the programmed cell death protein 1 ligand (PD-L1), a protein known to suppress the immune system through binding to a receptor found on cytotoxic T cells. Recent studies have established that PD-L1 is packaged into small EVs (sEVs), potentially contributing to the evasion of lung cancer cells from the immune system. Furthermore, it has been observed that large EVs (lEVs) are shed in significant quantities by tumor cells, with elevated levels of lEVs being associated with disease metastasis and cancer aggressiveness. The present study demonstrated that lEVs from nasopharyngeal carcinoma cells exhibit a significant enrichment of PD-L1. Furthermore, the EBV protein LMP1 was found to play a key role in regulating PD-L1 levels within these lEVs. These PD-L1+ lEVs containing LMP1 are likely to contribute to the immunosuppressive microenvironment found in EBV-associated cancers. IMPORTANCE A growing body of evidence has supported the notion that viruses utilize EVs and associated pathways to incorporate viral products. This allows for the evasion of an immune response while enabling viral spread within the host. Given that viral proteins often elicit strong antigenic peptides that are recognized by T cells, the regulation of the PD-L1 pathway through the overexpression of lEV-associated PD-L1 may serve as a strategy for immune evasion by viruses. The discovery that EBV LMP1 increases the secretion of PD-L1 in larger EVs identifies a new potential target for immune blockade therapy in EBV-associated cancers. Our findings may help to clarify the mechanism of LMP1-mediated enhancement of PD-L1 packaging into lEVs and may lead to the identification of more specific targets for treatment. Additionally, the identification of lEV biomarkers that predict a viral origin of disease could allow for more targeted therapies to be developed.