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Metabolic constraints in the tumor microenvironment constitute a barrier to effective antitumor immunity and similarities in the metabolic properties of T cells and cancer cells impede the specific therapeutic targeting of metabolism in either population. To identify distinct metabolic vulnerabilities of CD8+ T cells and cancer cells, we developed a high-throughput in vitro pharmacologic screening platform and used it to measure the cell type–specific sensitivities of activated CD8+ T cells and B16 melanoma cells to a wide array of metabolic perturbations during antigen-specific killing of cancer cells by CD8+ T cells. We illustrated the applicability of this screening platform by showing that CD8+ T cells were more sensitive to ferroptosis induction by inhibitors of glutathione peroxidase 4 (GPX4) than B16 and MC38 cancer cells. Overexpression of ferroptosis suppressor protein 1 (FSP1) or cytosolic GPX4 yielded ferroptosis-resistant CD8+ T cells without compromising their function, while genetic deletion of the ferroptosis sensitivity–promoting enzyme acyl-CoA synthetase long-chain family member 4 (ACSL4) protected CD8+ T cells from ferroptosis but impaired antitumor CD8+ T-cell responses. Our screen also revealed high T cell–specific vulnerabilities for compounds targeting NAD+ metabolism or autophagy and endoplasmic reticulum (ER) stress pathways. We focused the current screening effort on metabolic agents. However, this in vitro screening platform may also be valuable for rapid testing of other types of compounds to identify regulators of antitumor CD8+ T-cell function and potential therapeutic targets.

CD8+ T cell exhaustion is a state of dysfunction acquired in chronic viral infection and cancer, characterized by the formation of Slamf6+ progenitor exhausted and Tim-3+ terminally exhausted subpopulations through unknown mechanisms. Here we establish the phosphatase PTPN2 as a new regulator of the differentiation of the terminally exhausted subpopulation that functions by attenuating type 1 interferon signaling. Deletion of Ptpn2 in CD8+ T cells increased the generation, proliferative capacity and cytotoxicity of Tim-3+ cells without altering Slamf6+ numbers during lymphocytic choriomeningitis virus clone 13 infection. Likewise, Ptpn2 deletion in CD8+ T cells enhanced Tim-3+ anti-tumor responses and improved tumor control. Deletion of Ptpn2 throughout the immune system resulted in MC38 tumor clearance and improved programmed cell death-1 checkpoint blockade responses to B16 tumors. Our results indicate that increasing the number of cytotoxic Tim-3+CD8+ T cells can promote effective anti-tumor immunity and implicate PTPN2 in immune cells as an attractive cancer immunotherapy target.

T cell dysfunction is a hallmark of many cancers, but the basis for T cell dysfunction and the mechanisms by which antibody blockade of the inhibitory receptor PD-1 (anti-PD-1) reinvigorates T cells are not fully understood. Here we show that such therapy acts on a specific subpopulation of exhausted CD8(+) tumor-infiltrating lymphocytes (TILs). Dysfunctional CD8(+) TILs possess canonical epigenetic and transcriptional features of exhaustion that mirror those seen in chronic viral infection. Exhausted CD8(+) TILs include a subpopulation of ‘progenitor exhausted’ cells that retain polyfunctionality, persist long term and differentiate into ‘terminally exhausted’ TILs. Consequently, progenitor exhausted CD8(+) TILs are better able to control tumor growth than are terminally exhausted T cells. Progenitor exhausted TILs can respond to anti-PD-1 therapy, but terminally exhausted TILs cannot. Patients with melanoma who have a higher percentage of progenitor exhausted cells experience a longer duration of response to checkpoint-blockade therapy. Thus, approaches to expand the population of progenitor exhausted CD8(+) T cells might be an important component of improving the response to checkpoint blockade.

SUMMARYThe response of cytotoxic T cells to their cognate antigen involves rapid and broad changes in gene expression that are coupled with extensive chromatin remodeling. Here, we study the mechanisms by which the basic leucine zipper ATF-like transcription factor Batf helps regulate this process. Through genome-scale profiling, we observe critical roles for Batf in inducing transcriptional changes in stimulated naive cells, while affecting the chromatin at several levels, namely binding of key transcription factors, accessibility, and long range contacts. We identify a critical network of transcription factors that cooperate with Batf, including its binding partner Irf4, as well as Runx3 and T-bet, and demonstrate its synergistic activity in initiating aspects of the effector T cells’ transcriptional and epigenetic program in ectopically-induced fibroblasts. Our results provide a comprehensive resource for studying the epigenomic and transcriptomic landscape of effector differentiation of cytotoxic T cells.

Both tumor- and host-derived PD-L1 can play critical roles in immunosuppression; differences in tumor immunogenicity appear to underlie their relative contributions. Juneja et al. show that in immunogenic MC38 tumors, PD-L1 on tumor cells dominates in suppressing tumor immunity by inhibiting CD8 T cell cytotoxicity., It is unclear whether PD-L1 on tumor cells is sufficient for tumor immune evasion or simply correlates with an inflamed tumor microenvironment. We used three mouse tumor models sensitive to PD-1 blockade to evaluate the significance of PD-L1 on tumor versus nontumor cells. PD-L1 on nontumor cells is critical for inhibiting antitumor immunity in B16 melanoma and a genetically engineered melanoma. In contrast, PD-L1 on MC38 colorectal adenocarcinoma cells is sufficient to suppress antitumor immunity, as deletion of PD-L1 on highly immunogenic MC38 tumor cells allows effective antitumor immunity. MC38-derived PD-L1 potently inhibited CD8+ T cell cytotoxicity. Wild-type MC38 cells outcompeted PD-L1–deleted MC38 cells in vivo, demonstrating tumor PD-L1 confers a selective advantage. Thus, both tumor- and host-derived PD-L1 can play critical roles in immunosuppression. Differences in tumor immunogenicity appear to underlie their relative importance. Our findings establish reduced cytotoxicity as a key mechanism by which tumor PD-L1 suppresses antitumor immunity and demonstrate that tumor PD-L1 is not just a marker of suppressed antitumor immunity.

Obesity is a major cancer risk factor, but how differences in systemic metabolism change the tumor microenvironment (TME) and impact anti-tumor immunity is not understood. Here, we demonstrate that high-fat diet (HFD)-induced obesity impairs CD8(+) T cell function in the murine TME, accelerating tumor growth. We generate a single-cell resolution atlas of cellular metabolism in the TME, detailing how it changes with diet-induced obesity. We find that tumor and CD8(+) T cells display distinct metabolic adaptations to obesity. Tumor cells increase fat uptake with HFD, whereas tumor-infiltrating CD8(+) T cells do not. These differential adaptations lead to altered fatty acid partitioning in HFD tumors, impairing CD8(+) T cell infiltration and function. Blocking metabolic reprogramming by tumor cells in obese mice improves anti-tumor immunity. Analysis of human cancers reveals similar transcriptional changes in CD8(+) T cell markers, suggesting interventions that exploit metabolism to improve cancer immunotherapy.

T-cell exhaustion describes an acquired dysfunction common in settings of cancer and chronic viral infection. Despite clinical efforts to rescue exhaustion, the fundamental mechanisms specifying this state, and the potential for reprogramming exhausted T cells, remain poorly understood. We profiled accessible chromatin in chronic viral infection to show that exhausted CD8+ cells acquire a state-specific landscape of enhancers that profoundly differs from functional memory. Critically, CD8+ tumor-infiltrating lymphocytes shared significant epigenetic and transcriptional features with chronic viral infection, suggesting that T-cell exhaustion is a fundamental adaptation to settings of chronic stimulation. Comparison of mouse cells to those isolated from patients infected with HCV or HIV showed that the core epigenetic program of exhaustion is conserved across species. Importantly, curative therapy, which reduces viral antigen load, as well as anti-PD-1 immunotherapy, which reduces inhibitory T-cell signaling, failed to reverse the exhausted epigenetic profile. T-cell exhaustion is therefore a stable epigenetic state that is not rescued by common treatment modalities. We then sought new strategies to modulate T-cell exhaustion. We used Cas9-mediated genome editing to generate a novel mouse strain with germline deletion of a core exhaustion-associated enhancer near PD-1. We observed 2- to 3-fold enrichment in vivo of PD-1 enhancer-null cells over control cells in chronic infection, suggesting that CD8+ T cells in these mice might be less prone to exhaustion. PD-1 enhancer-null mice also exhibited slower tumor growth and increased survival when challenged with B16-ova melanoma. The establishment of a core program of T-cell exhaustion and increased insight into its epigenetic modulation has crucial implications for the future of immunotherapy and rational engineering of T cells for clinical use. This abstract is also being presented as Poster A3. Citation Format: Debattama R. Sen, Sarah A. Weiss, Brian C. Miller, Pierre Tonnerre, Rose Al Abosy, Kathleen B. Yates, Kevin Bi, Martin W. Lafleur, David Wolski, Lauer Georg, Arlene H. Sharpe, W. Nicholas Haining. Disrupting enhancers within the core epigenetic program of exhaustion improves T-cell responses and enhances tumor control [abstract]. In: Proceedings of the AACR Special Conference on Tumor Immunology and Immunotherapy; 2019 Nov 17-20; Boston, MA. Philadelphia (PA): AACR; Cancer Immunol Res 2020;8(3 Suppl):Abstract nr PR6.

Although PD-1 pathway inhibitors are revolutionizing cancer treatment, the mechanisms by which PD-1 regulates antitumor immunity are not fully understood. To determine PD-1 functions on different cell types, we used PD-1 conditional knockout mice. Subcutaneous transplantation of MC38 adenocarcinoma tumor cells in mice with complete deletion of PD-1 selectively on CD8+ T cells improved CD8+ T functions in the tumor microenvironment (TME). CD8+ T cells were required for the protective effects of PD-1 deletion in this model. To assess whether loss of PD-1 on all cells was necessary for improved antitumor immunity, we restricted PD-1 deletion to only half of the T-cell population. We hypothesized that a cell-intrinsic loss of PD-1 was necessary for improved T-cell fitness and effector functions. Here, deletion of PD-1 indeed led to T cell-intrinsic boosts in function. Unexpectedly, however, there was also a bystander effect that improved functions of PD-1-expressing CD8+ T cells in the TME. These data suggest that complete loss of PD-1 is not necessary for optimal tumor immunity, a finding that has important implications for applying PD-1-based immunotherapies to cancer patients. This abstract is also being presented as Poster B82. Citation Format: Kristen E. Pauken, Vikram R. Juneja, Alison Ringel, Jared H. Rowe, Kelly P. Burke, Peter T. Sage, Martin W. LaFleur, Juhi R. Kuchroo, Noga Ron-Harel, Seth Maleri, Jaclyn M. Long, Gordon J. Freeman, Nicolas Chevrier, Marcia C. Haigis, Arlene H. Sharpe. Loss of PD-1 promotes antitumor immunity by improving functions of both PD-1+ and PD-1- CD8+ T cells in the tumor microenvironment [abstract]. In: Proceedings of the AACR Special Conference on Tumor Immunology and Immunotherapy; 2019 Nov 17-20; Boston, MA. Philadelphia (PA): AACR; Cancer Immunol Res 2020;8(3 Suppl):Abstract nr PR9.

T-cell dysfunction in the tumor microenvironment (TME) is a hallmark of many cancers. Reinvigoration of T-cell function by PD-1 checkpoint blockade can result in striking clinical responses, but is only effective in a minority of patients. The mechanisms by which anti-PD-1 therapy acts on exhausted T cells are not fully understood. Here we show that anti-PD-1 therapy acts on a specific subpopulation of CD8+ tumor-infiltrating lymphocytes (TILs) in melanoma mouse models, which can also be found in patients with melanoma. Exhausted CD8+ TILs contain a subpopulation of “progenitor exhausted” T cells with critical functional attributes that are not shared by the majority “terminally exhausted” TILs: they retain more polyfunctionality, persist following transfer into tumor-bearing mice, and differentiate to repopulate terminally exhausted TILs in the TME. As a result, progenitor exhausted CD8+ TILs are better able to control tumor growth than terminally exhausted cells. Progenitor exhausted, but not terminally exhausted, CD8+ TILs can respond to anti-PD-1 therapy. Melanoma patients with a higher percentage of progenitor exhausted cells have a longer duration of response to checkpoint blockade therapy. Therefore, approaches to expand progenitor exhausted CD8+ T cells in the tumor microenvironment may be an important component of improving checkpoint blockade response. Citation Format: Brian C. Miller, Debattama R. Sen, Rose Al Abosy, Kevin Bi, Yamini Virkud, Martin W. LaFleur, Kathleen B. Yates, Ana Lako, Kristen Felt, Girish S. Naik, Michael Manos, Evisa Gjini, Jeffrey J. Ishizuka, F. Stephen Hodi, Scott J. Rodig, Arlene H. Sharpe, W. Nicholas Haining. Subsets of exhausted CD8+ T cells differentially mediate tumor control and respond to checkpoint blockade [abstract]. In: Proceedings of the AACR Special Conference on Tumor Immunology and Immunotherapy; 2019 Nov 17-20; Boston, MA. Philadelphia (PA): AACR; Cancer Immunol Res 2020;8(3 Suppl):Abstract nr A83.

T cell dysfunction in the tumor microenvironment (TME) is a hallmark of many cancers. Reinvigoration of T cell function by PD-1 checkpoint blockade can result in striking clinical responses, but is only effective in a minority of patients. The basis for T cell dysfunction in the TME, as well as the mechanisms by which anti-PD-1 therapy acts on dysfunctional T cells are not fully understood. Here we show that anti-PD-1 therapy acts on a specific subpopulation of CD8+ tumor-infiltrating lymphocytes (TILs) in melanoma mouse models, which can also be found in patients with melanoma. We find that dysfunctional CD8+ TILs possess canonical epigenetic and transcriptional features of T cell exhaustion, mirroring those seen in chronic viral infection. Similar to chronic viral infection, exhausted CD8+ TILs contain a subpopulation of “progenitor exhausted” T cells that have a distinct regulatory state. Progenitor exhausted TILs also have critical functional attributes that are not shared by the majority “terminally exhausted” TILs: they retain more polyfunctionality, persist following transfer into tumor-bearing mice, and differentiate to repopulate terminally exhausted TILs in the TME. As a result, progenitor exhausted CD8+ TILs are better able to control tumor growth than terminally exhausted cells. Progenitor exhausted, but not terminally exhausted, CD8+ TILs can respond to anti-PD-1 therapy but this occurs without reversion of their exhausted epigenetic state. Human melanomas contain CD8+ T cells with a progenitor exhausted phenotype and patients with a higher fraction of this subpopulation in their tumors have a significantly longer duration of response to combination checkpoint blockade therapy. Therefore, approaches to expand progenitor exhausted CD8+ T cells in the tumor microenvironment may be an important component of improving checkpoint blockade response. Citation Format: Brian C. Miller, Debattama R. Sen, Rose Al Abosy, Kevin Bi, Yamini V. Virkud, Martin W. LaFleur, Kathleen B. Yates, Ana Lako, Kristen Felt, Girish S. Naik, Michael Manos, Evisa Gjini, F. Stephen Hodi, Scott J. Rodig, Arlene H. Sharpe, W. Nicholas Haining. Functionally specialized subsets of exhausted CD8+ T cells mediate tumor control and differentially respond to checkpoint blockade [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 2701.

T-cell dysfunction in the tumor microenvironment (TME) is a hallmark of many cancers. Reinvigoration of T-cell function by PD-1 checkpoint blockade can result in striking clinical responses, but is effective only in a minority of patients. The basis for T-cell dysfunction in the TME, as well as the mechanisms by which anti-PD-1 therapy acts on dysfunctional T-cells are not fully understood. Here we show that anti-PD-1 therapy acts on a specific subpopulation of CD8+ tumor-infiltrating lymphocytes (TILs) in melanoma mouse models as well as patients with melanoma. We find that dysfunctional CD8+ TILs possess canonical epigenetic and transcriptional features of T-cell exhaustion, mirroring those seen in chronic viral infection. Similar to chronic viral infection, exhausted CD8+ TILs contain a subpopulation of “stem-like exhausted” T-cells that have a distinct regulatory state. Stem-like exhausted TILs also have critical functional attributes that are not shared by the majority “terminally exhausted” TILs: they retain more polyfunctionality, persist following transfer into tumor-bearing mice, and differentiate to repopulate terminally exhausted TILs in the TME. As a result, stem-like exhausted CD8+ TILs are better able to control tumor growth than terminally exhausted cells. Stem-like exhausted, but not terminally exhausted, CD8+ TILs can respond to anti-PD-1 therapy without reversion of their exhausted epigenetic state. CD8+ T-cells with a stem-like exhausted phenotype can be found in human melanoma samples and patients with a higher fraction of this subpopulation in their tumors have a significantly longer duration of response to combination checkpoint blockade therapy. Responsiveness to checkpoint blockade is therefore restricted to a subpopulation of exhausted TILs that retain specific functional properties which enable them to control tumors. Approaches to expand stem-like exhausted CD8+ T-cells in the tumor microenvironment may be an important component of improving checkpoint blockade response. Citation Format: Debattama R. Sen, Brian C. Miller, Rose Al Abosy, Kevin Bi, Martin W. LaFleur, Kathleen B. Yates, Ana Lako, Kristen D. Felt, Girish S. Naik, Michael Manos, Evisa Gjini, Yamini V. Virkud, Stephen Hodi, Scott J. Rodig, Arlene H. Sharpe, W. Nicholas Haining. Functionally specialized subsets of exhausted CD8+ T-cells mediate tumor control and response to checkpoint blockade [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 A216.

Although PD-1 pathway inhibitors are revolutionizing cancer treatment, the mechanisms by which PD-1 regulates anti-tumor immunity are not fully understood. Following subcutaneous transplantation of MC38 adenocarcinoma tumor cells into mice, we show that complete loss of PD-1 selectively on CD8+ T cells improved metabolic activity and functions in the tumor microenvironment (TME). Since clinically PD-1 inhibitors likely act on T cells post-priming, we next deleted PD-1 after initial priming and restricted deletion to roughly 50% of cells. Loss of PD-1 led to T cell-intrinsic boosts in metabolism and CD8+ T cells that lost PD-1 after priming preferentially formed anti-tumor memory cells, suggesting PD-1 antagonizes memory formation. Unexpectedly, there was also a bystander effect that improved functions of PD-1 expressing CD8+ T cells in the TME. These data suggest that complete loss of PD-1 is not necessary for optimal tumor immunity, and that enhancing the functions of a subset of CD8+ T cells can promote an antitumor microenvironment and immunologic memory. Citation Format: Kristen E. Pauken, Vikram R. Juneja, Peter T. Sage, Martin W. LaFleur, Juhi R. Kuchroo, Alison Ringel, Noga Ron-Harel, Seth P. Maleri, Gordon J. Freeman, Nicolas Chevrier, Marcia C. Haigis, Arlene H. Sharpe. PD-1 modulation promotes antitumor immunity by improving metabolic fitness of both PD-1+ and PD-1- CD8+ T cells in the tumor [abstract]. In: Proceedings of the AACR Special Conference on Tumor Immunology and Immunotherapy; 2017 Oct 1-4; Boston, MA. Philadelphia (PA): AACR; Cancer Immunol Res 2018;6(9 Suppl):Abstract nr A19.