Project description:Metabolic alteration influences cancer immunity. However, the role and mechanism of metabolic adaption on immune checkpoint blockade (ICB) responses remains ill-defined. Here, metabolomic profiling in mouse tumor models and cancer patients treated with ICB was performed. We found that metabolite inosine was associated with ICB sensitivity in mice and humans, and overcame ICB resistance in several mouse tumor models. Notably, inosine sensitized tumor cells to T cell-mediated cytotoxicity by amplifying tumor-intrinsic immunogenicity. Chemical proteomics further identified that inosine directly bound and inhibited ubiquitin-activating enzyme UBA6. Tumor intrinsic UBA6 loss augmented tumor immunogenicity and substituted the synergistic effect of inosine in combination with ICB. Clinically, tumor UBA6 expression negatively correlated with ICB response in cancer patients. Thus, we reveal an unappreciated function of inosine on tumor-intrinsic immunogenicity and UBA6 as a candidate target for immunotherapy.
Project description:Despite substantial progress that has been made in understanding how tumors escape immune surveillance, measures to counteract tumor immune evasion have been limited. Suppression of tumor antigen expression is a common adaptive mechanism that cancers use to evade detection and destruction by the immune system. Epigenetic modifications play a critical role in in various aspects of immune invasion, including the regulation of tumor antigen expression. To identify novel epigenetic regulators of tumor antigen expression, we established a transplantable syngeneic tumor model of immune escape with silenced antigen expression and used this system as a platform for a CRISPR-Cas9 suppressor screen targeting genes encoding epigenetic modifiers. We found that genetic disruption of the chromatin modifiers Atf7ip or its interacting partner Setdb1 in tumor cells restored tumor antigen expression, resulting in augmented tumor immunogenicity concomitant with elevated endogenous retroviral antigens (ERVs), mRNA intron retention. ERVs disinhibition was associated with a robust type I interferon response and increased T cell infiltration, leading to rejection of cells lacking intact Atf7ip or Setdb1. ATF7IP or SETDB1 expression inversely correlated with antigen processing and presentation pathways, interferon signaling, and T cell infiltration and cytotoxicity in human cancers. Our results provide a rationale for targeting Atf7ip or Setdb1 in cancer immunotherapy.
Project description:Epigenetic dysregulation is a defining feature of tumorigenesis and has been implicated in immune escape. However, the epigenetic mechanisms that drive immune evasion in cancer are poorly understood. To systematically identify epigenetic factors that modulate the immune sensitivity of tumor cells, we performed in vivo loss of function screens targeting 936 chromatin regulators in mouse tumor models treated with immune checkpoint blockade. We identified the H3K9-methyltransferase SETDB1 and other members of the HUSH and KAP1 complexes as cell-intrinsic mediators of immune escape in tumor cells. We also found that amplification of SETDB1 (1q21) in human tumors is associated with reduced cytotoxic T-cell infiltration and resistance to immune checkpoint blockade. Mechanistically, we demonstrate that SETDB1 targets broad domains, hundreds of kilobases in size, many of which reside within the open genome compartment. These SETDB1 domains are enriched for transposable elements (TEs) and immune gene clusters associated with segmental duplication events, a central mechanism of mammalian genome evolution. SETDB1 loss derepresses latent TE-encoded regulatory elements and proximal immune genes within these repetitive regions, including canonical NKG2D ligands, and induces hundreds of putative TE-encoded viral antigens. Our study establishes SETDB1 as an epigenetic checkpoint that suppresses intrinsic immunogenicity in cancer cells, and thus represents a candidate target for immunotherapy.
Project description:Anti-cancer immunity and response to immune therapy is influenced by the metabolic states of the tumours. Immune checkpoint blockade therapy (ICB) is known to involve metabolic adaptation, however, the mechanism is not fully known. Here we show, by metabolic profiling of plasma samples from melanoma-bearing mice undergoing anti-PD1 and anti-CTLA4 combination therapy, that higher levels of purine metabolites, including inosine, mark ICB sensitivity. Metabolic profiles of ICB-treated human cancers confirm the association between inosine levels and ICB sensitivity. In mouse models, inosine supplementation sensitizes tumours to ICB, even if they are intrinsically ICB resistant, by enhancing T cell-mediated cytotoxicity and hence generating an immunologically hotter microenvironment. We find that inosine directly inhibits UBA6 in tumour cells, and lower level of UBA6 makes the tumour more immunogenic and this is reflected in favourable outcome following ICB therapy in human melanomas. Transplanted mouse melanoma and breast cancer cells with genetic ablation of Uba6 show higher sensitivity to ICB than wild type tumours. Thus, we provide evidence of an inosine-regulated UBA6-dependent pathway governing tumour-intrinsic immunogenicity and hence sensitivity to immune checkpoint inhibition, which might provide targets to overcome ICB resistance.
Project description:Griffin GK, Wu J, Iracheta-Vellve A, Patti JC, Hsu J, Davis T, Dele-Oni D, Du PP, Halawi A, Ishizuka JJ, Kim S, Klaeger S, Knudsen NH, Miller BC, Nguyen T, Olander K, Papanastasiou M, Rachimi S, Robitschek EJ, Schneider EM, Yeary M, Zimmer M, Jaffe JD, Carr SA, Doench JG, Haining WN, Yates KB, Manguso RT, Bernstein BE. 2020. Epigenetic dysregulation is a defining feature of tumorigenesis and has been implicated in immune escape, yet mechanisms that drive immune evasion are poorly understood. To systematically identify epigenetic factors that modulate the immune sensitivity of tumor cells, we performed in vivo CRISPR-Cas9 screens targeting 936 chromatin regulators in mouse tumor models treated with immune checkpoint blockade. We identified the H3K9-methyltransferase SETDB1 and other members of the HUSH and KAP1 complexes as cell-intrinsic mediators of immune escape in tumor cells. We also found that amplification of SETDB1 (1q21) in human tumors is associated with reduced cytotoxic T-cell infiltration and resistance to immune checkpoint blockade. Mechanistically, we demonstrate that SETDB1 represses broad domains, hundreds of kilobases in size, many of which reside within the open genome compartment. These SETDB1 domains are enriched for transposable elements (TEs) and immune gene clusters associated with segmental duplication events, a central mechanism of mammalian genome evolution. SETDB1 loss derepresses latent TE-encoded regulatory elements and proximal immune genes within these repetitive regions, including canonical co-stimulatory ligands, and induces hundreds of putative TE-encoded viral antigens. Our study establishes SETDB1 as an epigenetic checkpoint that suppresses intrinsic immunogenicity in cancer cells, and thus represents a candidate target for immunotherapy.