Abstract 4694: The contribution of Epstein-Barr virus to the impaired T-cell responses in nasopharyngeal carcinoma
Authors: Lee Hui Min , Haigh Tracey , Tsao George SW , Murray Paul G. , Taylor Graham , Paterson Ian C. , Yap Lee Fah 
Published: August 2018

Undifferentiated nasopharyngeal carcinoma (NPC) is a geographically skewed disease in which more than 80% cases are from southern China and Southeast Asia. NPC is consistently associated with Epstein-Barr virus (EBV) infection and characterized by a prominent lymphocyte infiltration. The consistent expression of EBV proteins in NPC cells has led to several clinical trials of adoptive T-cell therapy or vaccination to boost the immune response to EBV antigens. However, these treatments yield relatively modest clinical benefit, which may be due to varying degrees of immunosuppression in the tumor microenvironment. The lack of model systems to analyze the ability of therapeutically relevant T cells to recognize and kill NPC cells represents a fundamental limitation in our attempts to harness the immune system for clinical benefit. We used three NPC cell lines as targets in T-cell assays, together with a panel of established HLA-matched EBV-specific CD8 and CD4 T-cell clones. T-cell activity and killing were measured by IFN-γ ELISA and outgrowth assays, respectively. We demonstrate, for the first time, that NPC cells can be recognized and killed by EBV-specific T-cell clones in vitro, which suggests that tumor-derived factors inhibit such responses in vivo. These observations are consistent with the previous reported functional inactivation of EBV-specific cytotoxic T lymphocytes (CTL) in NPC patients. We hypothesized that EBV infection of NPC cells induces the secretion of immunosuppressive factors. The effect of conditioned media derived from an EBV-infected premalignant nasopharyngeal cell line, NP460htert, on T-cell activity was examined by treating several clones of EBV-specific CTLs in vitro. The conditioned media inhibited the secretion of IFN-γ from peptide-stimulated CTLs, indicating that secreted factors that could suppress CTL functions are induced following EBV infection in NP460htert cells. RNA sequencing analyses on NP460hTert and three NPC cell lines following EBV infection revealed a significant enrichment of genes whose proteins are located at extracellular region/matrix, including a number of immunomodulators. Our results suggest that EBV infection might induce the production of soluble molecules, which in turn suppress the antitumor T-cell responses. In conclusion, we have developed a system with which to study NPC-specific immune responses and shown that soluble factors induced by EBV infection can suppress T-cell activity. These model systems will be critical in the future to examine the effects of checkpoint inhibitors, secreted factors from cancer-associated fibroblasts or NPC cells upon T-cell activity, which will ultimately enhance the success of EBV-targeted immunotherapy strategies.

Citation Format: Hui Min Lee, Tracey Haigh, George SW Tsao, Paul G. Murray, Graham Taylor, Ian C. Paterson, Lee Fah Yap. The contribution of Epstein-Barr virus to the impaired T-cell responses in nasopharyngeal carcinoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 4694.