Abstract 1687: Tumor methionine metabolism drives T-cell exhaustion in hepatocellular carcinoma
Authors: Hung Man Hsin , Lee Joo Sang , Heinrich Sophia , Chan Ching Wen , Ma Lichun , Forgues Marshonna , Budhu Anuradha , Chaisaingmongko Jittiporn , Ruchirawat Mathuros , Ruppin Eytan , Wang Xin Wei 
Published: September 2020

Abstract
Introduction
Exhausted T cells (ETC) denotes a hypofunctional state of T lymphocyte that is commonly seen in cancer. Chronic T-cell receptor stimulation and recruitment of immune suppressive cells from the tumor microenvironment have been implicated as the mechanisms driving ETC. However, the roles of tumor cells in promoting ETC has remained elusive. Tumor metabolism is a core cancer hallmark. While metabolic alterations of cancer cells are required to support the anabolic requirement of cellular growth and proliferation, they may also affect the composition and function of the non-cancer cells residing in the same microenvironment. Bioinformatically searching the interaction between ETC and tumor metabolism may facilitate the identification of tumor drivers and novel mechanisms attributing ETC in hepatocellular carcinoma (HCC).
Method
HCC-specific ETC molecular signature was identified from single cell RNA sequencing of HCC-infiltrating lymphocytes and global transcriptome of HCC tumors. Correlation analysis of ETC and tumor-associated genomics, transcriptome and metabolomics was carried out. The clinical impact of ETC and ETC-associated metabolic alterations were investigated. Biological functions of the ETC-associated tumor metabolites were also assessed in vitro on human CD8+ T cells isolated form health donors.
Results
By exploring the single-cell transcriptome profiles of 5,063 HCC-derived lymphocytes, we identified 82 ETC-specific genes and found that ETC status robustly predicts patient survival in three independent HCC cohort, comparing 675 patients. While the degree of ETC is negatively correlated with the activity of effector T cell in HCC tumor tissues and liver tissues with chronic inflammation, such relationship was not observed in non-cancerous patients with acute inflammatory conditions. An integrated analysis of tumor-associated genomics, transcriptomics and metabolomics identifies an oncogenic reprograming of HCC methionine recycling towards salvage pathway leads to the elevation of 5-methylthioadenosine (MTA) and S-adenosylmethionine (SAM), which are associated with ETC status and clinical prognosis of HCC patients. Consistent with these clinical findings, SAM and MTA inhibit T cell activation in vitro. Furthermore, using assay for transposase-accessible chromatin with high-throughput sequencing, we found that SAM/MTA treatment reduces global chromatin accessibilities in CD8+ T cells, leading to T cell dysfunction. Lastly, we showed that MTA level in the serum may serve as a biomarker of ETC and HCC patient survival.
Conclusion
Our results identify reprogramming of tumor methionine metabolism as a key metabolic mechanism by which HCC tumor drive ETC and evade an immune attack.
Citation Format: Man Hsin Hung, Joo Sang Lee, Sophia Heinrich, Ching Wen Chan, Lichun Ma, Marshonna Forgues, Anuradha Budhu, Jittiporn Chaisaingmongko, Mathuros Ruchirawat, Eytan Ruppin, Xin Wei Wang. Tumor methionine metabolism drives T-cell exhaustion in hepatocellular carcinoma [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 1687.