Research ArticleCANCER IMMUNOLOGY

Tumor immune evasion arises through loss of TNF sensitivity

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Science Immunology  18 May 2018:
Vol. 3, Issue 23, eaar3451
DOI: 10.1126/sciimmunol.aar3451

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Killing without poking holes

Given the success of T cell–centric cancer immunotherapies, there is considerable interest in understanding exactly how tumors evade this form of therapy. Kearney et al. carried out a series of genome-wide CRISPR screens to identify mechanisms of tumor immune evasion from cytotoxic T lymphocytes (CTLs) and natural killer (NK) cells. They found IFN-γ signaling and antigen presentation to be critical for CTL-mediated killing of cancer cells and uncovered TNF signaling as a key effector mechanism for both CTL and NK cell antitumor activity. The same immune evasion mechanisms arose upon screening with perforin-deficient CTLs, suggesting that tumors evade the immune system by dampening the effects of cytokines, not direct killing via perforin.

Abstract

Immunotherapy has revolutionized outcomes for cancer patients, but the mechanisms of resistance remain poorly defined. We used a series of whole-genome clustered regularly interspaced short palindromic repeat (CRISPR)–based screens performed in vitro and in vivo to identify mechanisms of tumor immune evasion from cytotoxic lymphocytes [CD8+ T cells and natural killer (NK) cells]. Deletion of key genes within the tumor necrosis factor (TNF) signaling, interferon-γ (IFN-γ) signaling, and antigen presentation pathways provided protection of tumor cells from CD8+ T cell–mediated killing and blunted antitumor immune responses in vivo. Deletion of a number of genes in the TNF pathway also emerged as the key mechanism of immune evasion from primary NK cells. Our screens also identified that the metabolic protein 2-aminoethanethiol dioxygenase (Ado) modulates sensitivity to TNF-mediated killing by cytotoxic lymphocytes and is required for optimal control of tumors in vivo. Remarkably, we found that tumors delete the same genes when exposed to perforin-deficient CD8+ T cells, demonstrating that the dominant immune evasion strategy used by tumor cells is acquired resistance to T cell–derived cytokine-mediated antitumor effects. We demonstrate that TNF-mediated bystander killing is a potent T cell effector mechanism capable of killing antigen-negative tumor cells. In addition to highlighting the importance of TNF in CD8+ T cell– and NK cell–mediated killing of tumor cells, our study also provides a comprehensive picture of the roles of the TNF, IFN, and antigen presentation pathways in immune-mediated tumor surveillance.

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