Targeting Mhc Class I Molecules And Immune Checkpoints As Key Immune Evasion Strategies In Ebv-Associated Nasopharyngeal Carcinoma

Nasopharyngeal carcinoma (NPC) is a distinct type of head and neck cancer that is consistently associated with intensive lymphocytes infiltration and Epstein-Barr virus infection. This study aims at elucidating the mechanism contributing to immune evasion in NPC. During NPC tumorigenesis, multiple intrinsic mechanisms are acquired to escape cellular immune response for the tumor and viral antigens. By genome sequencing, somatic alterations of multiple MHC class I genes including NLRC5, HLA-A, HLA-B, HLA-C and B2M were detected in 30% of primary NPC. Significant correlation of MHC class I gene alterations and poor survival rate in the patients was also shown. The finding suggested that the deficiency of antigen presentation mechanism represents a common strategy for immune evasion in NPC and favors rapid tumor progression. Losses of HLA-A, HLA-B and NLRC5 expression were validated in a panel of NPC tumor lines and selected primary tumors. The role of NLRC5 as key transcription regulator of HLA-A and HLA-B expression was demonstrated in the nasopharyngeal epithelial cells. To further evaluate the mechanisms contributed to immune evasion in NPC, we have elucidated immunosuppressive molecules involved in immune surveillance in Epstein Barr Virus (EBV)-associated NPC and its association with EBV-encoded LMP1 in an independent cohort of primary NPCs. By immunohistochemistry, the expression of EBV-encoded LMP1, MHC class I genes and various immunosuppressive molecules including PDL1, PDL2 and IDO1 was examined in 98 primary tumors. PDL1 and PDL2 were found to be over-expressed in 50% and 33.7% of NPC cases while IDO1 was found to be expressed in 28.8% of cases. Primary NPC cases expressing either PDL1 or PDL2 accounted for 64.3%. A significant association between LMP1 and PDL1 and PDL2 expression was also found. The correlation of PDL1, PDL2 and/or MHC class I molecule expression with the outcome of the patients was determined. The high incidence of MHC class I deficiencies and PDL1/PDL2 overexpression imply that EBV-associated NPC escape from the host immune response by targeting both antigen presentation mechanisms and immune checkpoints. Our findings also suggested that the expression of MHC class I molecules and PDL1/PDL2 is a potential biomarker for immunotherapy in NPC patients. Citation Format: Sharie Pui-Kei Siu, Ka Fai To, Grace Tin-Yun Chung, Vivian W.Y. Lui, Yvonne Y. Li, Peter S. Hammerman, Kwok Wai Lo. Targeting MHC class I molecules and immune checkpoints as key immune evasion strategies in EBV-associated nasopharyngeal carcinoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 646. doi:10.1158/1538-7445.AM2017-646