LAUSR

Type III Nasopharyngeal carcinoma (NPC) is characterized by Epstein-Barr virus (EBV) infection and immune infiltration. M2 macrophages in the NPC microenvironment are considered to associate with poorer prognosis and promote disease progression. How the tumor-derived EBV or viral products regulate macrophage polarization within NPC microenvironment remains to be explored. We demonstrated that EBV products can be transferred to uninfected cancer cells or stromal cells via exosomes. The exosome-mediated intercellular communications between EBV+-NPC cells and macrophages were further investigated. Results of mass spectrometry and western blotting showed that NPC cells deposited EBV-encoded latent protein 1 (LMP1) into exosomes. The uptake of these exosomes by human monocyte-derived macrophages led to a M2-dominant polarization. Specifically, multiple properties of M2 macrophages, including higher levels of CD206, CD163, CD209, and VEGF, as well as a reduced expression of iNOS were found in macrophages stimulated with LMP1-containing exosomes (LMP1_exosomes), compared to those treated with exosomes derived from EBV-negative NPC cells. The LMP1_exosome-treated macrophages also exhibited a reduced cytotoxicity towards primary cancer cells. RNA sequencing data revealed that LMP1_exosomes suppressed the function of antigen presentation while activating the macrophage stimulating 1 receptor (MST1R)-STAT3 signaling in macrophages. Results of mechanistic studies showed that LMP1-CTAR2 domain contributed to the activation of MST1R. Additionally, treating macrophages with LMP1_exosomes activated yes-associated protein 1 (YAP1), the LMP1-mediated M2 phenotype and MST1R expression were partially suppressed by treating cells with the YAP1 inhibitor (verteporfin). It appears that YAP1 acts as a key regulator of MST1R. Clinically, higher expressions of MST1R and nuclear YAP1 were correlated with disease progression of NPC (p < 0.001). The role of LMP1_exosomes in regulating macrophage immune responses was further investigated using single-cell RNA sequencing (scRNA-seq) technique. Results showed that treating primary macrophages isolated from human head and neck tumors with LMP1_exosomes resulted in an increase in M2 proportion. Results of gene set variation analysis (GSVA) demonstrated enhanced signatures in IL10 and VEGF signalings. Collectively, our data suggest that LMP1-containing exosomes facilitate M2 macrophage polarization, which may assist cancer immune evasion in the NPC microenvironment. Citation Format: Tzu-Tung Liu, Yun-Hua Sui, Fang-Yu Tsai, Shih-Sheng Jiang, Kai-Ping Chang, Chen-Han Huang, Shu-Chen Liu. EBV positive NPC-derived exosomes promote macrophage M2 polarization via activating MST1R and YAP1 signalings [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 2500.