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Abstract A215: Thymocyte selection-associated HMG box protein TOX is a master regulator of tumor-specific T-cell dysfunction

Tumor-specific CD8 T-cells in cancers enter a state of dysfunction characterized by the expression of inhibitory receptors and failure to produce effector cytokines and cytotoxic molecules. Here we identify the nuclear factor, Thymocyte selection-associated HMG box protein, TOX, as a master regulator of tumor-specific T-cell dysfunction. TOX is uniquely expressed in dysfunctional CD8 T-cells from mouse and human tumors but absent in functional T-cells. TOX expression is driven by continuous TCR stimulation and NFAT activity. Forced expression of TOX in functional effector T-cells was sufficient to induce a transcriptional program of dysfunction through the concerted expression of genes encoding numerous inhibitory receptors and dysfunction-associated transcription factors. Notably, TOX-deficient tumor-infiltrating T-cells did not upregulate inhibitory receptors such as PD1, LAG3, CD38, or CD39 and maintained high TCF1 expression. Surprisingly, despite their normal, “non-exhausted” phenotype, TOX-deficient T-cells failed to make effector cytokines, suggesting that loss of effector function in tumor-specific T-cells is uncoupled from inhibitory receptor expression. Furthermore, TOX-deficient T-cells failed to persist in tumors, ultimately undergoing activation-induced cell death. We propose that the TOX-induced transcriptional program of hyporesponsiveness is a physiologic negative feedback mechanism that prevents overstimulation; thus TOX is absolutely required for T-cell survival in the setting of chronic antigen stimulation as in cancers. Citation Format: Andrew C. Scott, Steven Camara, Peter Lauer, Alexandra Synder, Dmitriy Zamarin, Tyler Walther, Olivier Levy, Michael Glickman, Jonathan Kaye, Mary Philip, Andrea Schietinger. Thymocyte selection-associated HMG box protein TOX is a master regulator of tumor-specific T-cell dysfunction [abstract]. In: Proceedings of the Fourth CRI-CIMT-EATI-AACR International Cancer Immunotherapy Conference: Translating Science into Survival; Sept 30-Oct 3, 2018; New York, NY. Philadelphia (PA): AACR; Cancer Immunol Res 2019;7(2 Suppl):Abstract nr A215.