TOX promotes the exhaustion of antitumor CD8(+) T cells by preventing PD1 degradation in hepatocellular carcinoma.
The thymocyte selection-associated high mobility group box protein (TOX) plays a vital role in T cell development and differentiation, however, its role in T cell exhaustion was unexplored. Here, we aim to investigate the role of TOX in regulating the antitumor effect of CD8+ T cells in hepatocellular carcinoma.
Fully functional, partially and severely exhausted tumor-infiltrating CD8+ T cells were sorted by flow cytometry and subjected to transcriptome sequencing analysis. Upregulated TOX expression was validated by flow cytometry. The antitumor function of CD8+ T cells with TOX downregulation or overexpression was studied in a mouse HCC model and HCC patient-derived xenograft mouse model. Transcriptome sequencing analysis was performed in TOX-overexpressing and control CD8+ T cells. The mechanism underlying the TOX-mediated regulation of PD1 expression was studied by laser confocal detection, immune co-precipitation and flow cytometer.
TOX was upregulated in exhausted CD8+ T cells in hepatocellular carcinoma. TOX downregulation in CD8+ T cells inhibited tumor growth, increased CD8+ T cell infiltration, alleviated CD8+ T cell exhaustion and improved the anti-PD1 response of CD8+ T cells. The mechanism behind this involved the binding of TOX to PD1 in the cytoplasm, which facilitated the endocytic recycling of PD1, thus maintaining abundant PD1 expression at the cell surface. High expression of TOX in peripheral CD8+ T cells correlated with poorer anti-PD1 responses and prognosis.
TOX promotes CD8+ T cell exhaustion in hepatocellular carcinoma by regulating endocytic recycling of PD1. Downregulating TOX expression in CD8+ T cells exerts synergistic effects with anti-PD1 therapy, highlighting a promising strategy for cancer immunotherapy.
Abundant TOX expression in CD8+ T cells impairs their antitumor function in hepatocellular carcinoma. Mechanically, TOX reduces PD1 degradation and promotes PD1 translocation to the cell surface in CD8+ T cells, thus maintaining high PD1 expression at the cell surface. Downregulating TOX expression improves the antitumor function of CD8+ T cells, which shows the synergetic role of anti-PD1 therapy, highlighting a promising strategy for enhancement of cancer immunotherapy.
Wang X
，He Q
，Shen H
，Xia A
，Tian W
，Yu W
，Sun B
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TIGIT and PD1 Co-blockade Restores ex vivo Functions of Human Tumor-Infiltrating CD8(+) T Cells in Hepatocellular Carcinoma.
TIGIT is a co-inhibitory receptor, and its suitability as a target for cancer immunotherapy in HCC is unknown. PD1 blockade is clinically effective in about 20% of advanced HCC patients. Here we aim to determine whether co-blockade of TIGIT/PD1 has added value to restore functionality of HCC tumor-infiltrating T cells (TILs).
Mononuclear leukocytes were isolated from tumors, paired tumor-free liver tissues (TFL) and peripheral blood of HCC patients, and used for flow cytometric phenotyping and functional assays. CD3/CD28 T-cell stimulation and antigen-specific assays were used to study the ex vivo effects of TIGIT/PD1 single or dual blockade on T-cell functions.
TIGIT was enriched, whereas its co-stimulatory counterpart CD226 was down-regulated on PD1high CD8+ TILs. PD1high TIGIT+ CD8+ TILs co-expressed exhaustion markers TIM3 and LAG3 and demonstrated higher TOX expression. Furthermore, this subset showed decreased capacity to produce IFN-γ and TNF-α. Expression of TIGIT-ligand CD155 was up-regulated on tumor cells compared with hepatocytes in TFL. Whereas single PD1 blockade preferentially enhanced ex vivo functions of CD8+ TILs from tumors with PD1high CD8+ TILs (high PD1 expressers), co-blockade of TIGIT and PD1 improved proliferation and cytokine production of CD8+ TILs from tumors enriched for PD1int CD8+ TILs (low PD1 expressers). Importantly, ex vivo co-blockade of TIGIT/PD1 improved proliferation, cytokine production, and cytotoxicity of CD8+ TILs compared with single PD1 blockade.
Ex vivo, co-blockade of TIGIT/PD1 improves functionality of CD8+ TILs that do not respond to single PD1 blockade. Therefore co-blockade of TIGIT/PD1 could be a promising immune therapeutic strategy for HCC patients.
Ge Z
，Zhou G
，Campos Carrascosa L
，Gausvik E
，Boor PPC
，Noordam L
，Doukas M
，Polak WG
，Terkivatan T
，Pan Q
，Takkenberg RB
，Verheij J
，Erdmann JI
，IJzermans JNM
，Peppelenbosch MP
，Kraan J
，Kwekkeboom J
，Sprengers D
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《Cellular and Molecular Gastroenterology and Hepatology》
Disruption of SIRT7 Increases the Efficacy of Checkpoint Inhibitor via MEF2D Regulation of Programmed Cell Death 1 Ligand 1 in Hepatocellular Carcinoma Cells.
Immune checkpoint inhibitors have some efficacy in the treatment of hepatocellular carcinoma (HCC). Programmed cell death 1 ligand 1 (PD-L1), expressed on some cancer cells, binds to the receptor programmed cell death 1 (PDCD1, also called PD1) on T cells to prevent their proliferation and reduce the antigen-tumor immune response. Immune cells that infiltrate some types of HCCs secrete interferon gamma (IFNG). Some HCC cells express myocyte enhancer factor 2D (MEF2D), which has been associated with shorter survival times of patients. We studied whether HCC cell expression of MEF2D regulates expression of PD-L1 in response to IFNG.
We analyzed immune cells from 20 fresh HCC tissues by flow cytometry. We analyzed 225 fixed HCC tissues (from 2 cohorts) from patients in China by immunohistochemistry and obtained survival data. We created mice with liver-specific knockout of MEF2D (MEF2DLPC-KO mice). We knocked out or knocked down MEF2D, E1A binding protein p300 (p300), or sirtuin 7 (SIRT7) in SMMC-7721, Huh7, H22, and Hepa1-6 HCC cell lines, some incubated with IFNG. We analyzed liver tissues from mice and cell lines by RNA sequencing, immunoblot, dual luciferase reporter, and chromatin precipitation assays. MEF2D protein acetylation and proteins that interact with MEF2D were identified by coimmunoprecipitation and pull-down assays. H22 cells, with MEF2D knockout or without (controls), were transplanted into BALB/c mice, and some mice were given antibodies to deplete T cells. Mice bearing orthotopic tumors grown from HCC cells, with or without knockout of SIRT7, were given injections of an antibody against PD1. Growth of tumors was measured, and tumors were analyzed by immunohistochemistry and flow cytometry.
In human HCC specimens, we found an inverse correlation between level of MEF2D and numbers of CD4+ and CD8+ T cells; level of MEF2D correlated with percentages of PD1-positive or TIM3-positive CD8+ T cells. Knockout of MEF2D from H22 cells reduced their growth as allograft tumors in immune-competent mice but not in immune-deficient mice or mice with depletion of CD8+ T cells. When MEF2D-knockout cells were injected into immune-competent mice, they formed smaller tumors that had increased infiltration and activation of T cells compared with control HCC cells. In human and mouse HCC cells, MEF2D knockdown or knockout reduced expression of PD-L1. MEF2D bound the promoter region of the CD274 gene (encodes PD-L1) and activated its transcription. Overexpression of p300 in HCC cells, or knockout of SIRT7, promoted acetylation of MEF2D and increased its binding, along with acetylated histones, to the promoter region of CD274. Exposure of HCC cells to IFNG induced expression of p300 and its binding MEF2D, which reduced the interaction between MEF2D and SIRT7. MEF2D-induced expression of PD-L1 upon IFNG exposure was independent of interferon-regulatory factors 1 or 9. In HCC cells not exposed to IFNG, SIRT7 formed a complex with MEF2D that attenuated expression of PD-L1. Knockout of SIRT7 reduced proliferation of HCC cells and growth of tumors in immune-deficient mice. Compared with allograft tumors grown from control HCC cells, in immune-competent mice, tumors grown from SIRT7-knockout HCC cells expressed higher levels of PD-L1 and had reduced infiltration and activation of T cells. In immune-competent mice given antibodies to PD1, allograft tumors grew more slowly from SIRT7-knockout HCC cells than from control HCC cells.
Expression of MEF2D by HCC cells increases their expression of PD-L1, which prevents CD8+ T-cell-mediated antitumor immunity. When HCC cells are exposed to IFNG, p300 acetylates MEF2D, causing it to bind the CD274 gene promoter and up-regulate PD-L1 expression. In addition to promoting HCC cell proliferation, SIRT7 reduced acetylation of MEF2D and expression of PD-L1 in HCC cells not exposed to IFNG. Strategies to manipulate this pathway might increase the efficacy of immune therapies for HCC.
Xiang J
，Zhang N
，Sun H
，Su L
，Zhang C
，Xu H
，Feng J
，Wang M
，Chen J
，Liu L
，Shan J
，Shen J
，Yang Z
，Wang G
，Zhou H
，Prieto J
，Ávila MA
，Liu C
，Qian C
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