Tumor-infiltrating DCs suppress nucleic acid-mediated innate immune responses through interactions between the receptor TIM-3 and the alarmin HMGB1

Life after death: targeting high mobility group box 1 in emergent cancer therapies

High mobility group box 1 (HMGB1), an evolutionarily highly conserved and abundant nuclear protein also has roles within the cytoplasm and as an extracellular damage-associated molecular pattern (DAMP) molecule. Extracellular HMGB1 is the prototypic endogenous 'danger signal' that triggers inflammation and immunity. Recent findings suggest that posttranslational modifications dictate the cellular localization and secretion of HMGB1. HMGB1 is actively secreted from immune cells and stressed cancer cells, or passively released from necrotic cells. During cancer development or administration of therapeutic agents including chemotherapy, radiation, epigenetic drugs, oncolytic viruses, or immunotherapy, the released HMGB1 may either promote or limit cancer growth, depending on the state of progression and vascularization of the tumor. Extracellular HMGB1 enhances autophagy and promotes persistence of surviving cancer cells following initial activation. When oxidized, it chronically suppresses the immune system to promote cancer growth and progression, thereby enhancing resistance to cancer therapeutics. In its reduced form, it can facilitate and elicit innate and adaptive anti-tumor immunity, recruiting and activating immune cells, in conjunction with cytotoxic agents, particularly in early transplantable tumor models. We hypothesize that HMGB1 also functions as an epigenetic modifier, mainly through regulation of NF-kB-dependent signaling pathways, to modulate the behavior of surviving cancer cells as well as the immune cells found within the tumor microenvironment. This has significant implications for developing novel cancer therapeutics.

Expression and anatomical distribution of TIM-containing molecules in Langerhans cell sarcoma

Signals from the T cell immunoglobulin and mucin-domain (TIM)-containing molecules have been demonstrated to be involved in regulating the progress of carcinoma. However, the expression and anatomical distribution of TIMs in Langerhans cell sarcoma (LCS), which is a rare malignancy derived from dendritic cells of the epidermis, has yet to be determined. In this study, the expression of TIM-1, TIM-3 and TIM-4 in LCS samples were detected by immunohistochemistry. Our results showed that these three molecules were found in LCS sections. At the cellular level, these molecules were found on the cell membrane and in the cytoplasm. Immunofluorescence double-staining demonstrated that these TIMs were co-expressed with Langerin, a potential biomarker for detecting LCS. In addition, TIM-1 was also expressed on CD68(+) macrophages and CK-18(+) epithelial cells, while TIM-3 and TIM-4 were expressed on all cell types investigated, including CD3(+)T cells, CD68(+) macrophages, CD11c(+) dendritic cells, CD16(+) NK Cells, CD31(+) endothelial cells and CK-18(+) epithelial cells. Interestingly, TIMs were also co-expressed with some members of the B7 superfamily, including B7-H1, B7-H3 and B7-H4 on sarcoma cells. Our results clearly showed the characteristic expression and anatomical distribution of TIMs in LCS, and a clear understanding of their functional roles may further elucidate the pathogenesis of this carcinoma and potentially contribute to the development of novel immunotherapeutic strategies.

A Janus tale of two active high mobility group box 1 (HMGB1) redox states

High mobility group box 1 (HMGB1), the prototypic damage-associated molecular pattern molecule, is released at sites of inflammation and/or tissue damage. There, it promotes cytokine production and chemokine production/cell migration. New work shows that the redox status of HMGB1 distinguishes its cytokine-inducing and chemokine activity. Reduced all-thiol-HMGB1 has sole chemokine activity, whereas disulfide-HMGB1 has only cytokine activity, and oxidized, denatured HMGB1 has neither. Autophagy (programmed cell survival) and apoptosis (programmed cell death) have been implicated in controlling both innate and adaptive immune functions. Reduced HMGB1 protein promotes autophagy, whereas oxidized HMGB1 promotes apoptosis. Thus, the differential activity of HMGB1 in immunity, inflammation and cell death depends on the cellular redox status within tissues.

Immunogenic cell death and DAMPs in cancer therapy

Although it was thought that apoptotic cells, when rapidly phagocytosed, underwent a silent death that did not trigger an immune response, in recent years a new concept of immunogenic cell death (ICD) has emerged. The immunogenic characteristics of ICD are mainly mediated by damage-associated molecular patterns (DAMPs), which include surface-exposed calreticulin (CRT), secreted ATP and released high mobility group protein B1 (HMGB1). Most DAMPs can be recognized by pattern recognition receptors (PRRs). In this Review, we discuss the role of endoplasmic reticulum (ER) stress and reactive oxygen species (ROS) in regulating the immunogenicity of dying cancer cells and the effect of therapy-resistant cancer microevolution on ICD.

T Cell Immunoglobulin Mucin Domain (TIM)-3 Promoter Activity in a Human Mast Cell Line

T cell immunoglobulin mucin domain (TIM)-3 is an immunomodulatory molecule and upregulated in T cells by several cytokines. TIM-3 also influences mast cell function but its transcriptional regulation in mast cells has not been clarified. Therefore, we examined the transcript level and the promoter activity of TIM-3 in mast cells. The TIM-3 transcript level was assessed by real-time RT-PCR and promoter activity by luciferase reporter assay. TIM-3 mRNA levels were increased in HMC-1, a human mast cell line by TGF-β1 stimulation but not by stimulation with interferon (IFN)-α, IFN-λ, TNF-α, or IL-10. TIM-3 promoter -349~+144 bp region relative to the transcription start site was crucial for the basal and TGF-β1-induced TIM-3 promoter activities in HMC-1 cells. TIM-3 promoter activity was increased by overexpression of Smad2 and Smad4, downstream molecules of TGF-β1 signaling. Our results localize TIM-3 promoter activity to the region spanning -349 to +144 bp in resting and TGF-β1 stimulated mast cells.

High-mobility group box family of proteins: ligand and sensor for innate immunity

Recent discoveries in signal-transducing innate receptors have illustrated the close link between innate and adaptive immunity. These advances revisit a fundamental issue of immunology, the recognition of self and non-self molecules by the immune system. Indeed, mounting evidence has been provided that the sensing of self-derived molecules by the immune system is important for health and disease. The high-mobility group box (HMGB) proteins, particularly HMGB1, are self-derived immune activators that have multiple functions in the regulation of immunity and inflammation. In this review, we summarize current knowledge of the function of HMGB proteins, as a ligand that can evoke inflammatory responses, and as a sensor for nucleic-acid-mediated immune responses.

MicroRNA-466l inhibits antiviral innate immune response by targeting interferon-alpha

Effective recognition of viral infections and subsequent triggering of antiviral innate immune responses are essential for the host antiviral defense, which is tightly regulated by multiple regulators, including microRNAs (miRNAs). A previous study showed that miR-466l upregulates IL-10 expression in macrophages by antagonizing RNA-binding protein tristetraprolin-mediated IL-10 mRNA degradation. However, the ability of miR-466l to regulate antiviral immune responses remains unknown. Here, we found that interferon-alpha (IFN-α) expression was repressed in Sendai virus (SeV)- and vesicular stomatitis virus (VSV)-infected macrophages and in dendritic cells transfected with miR-466l expression. Moreover, multiple IFN-α species can be directly targeted by miR-466l through their 3' untranslated region (3'UTR). This study has demonstrated that miR-466l could directly target IFN-α expression to inhibit host antiviral innate immune response.

Tumor immunity times out: TIM-3 and HMGB1

The characteristics of the tumor microenvironment vary widely. New work shows that after tumor-associated expression of the receptor TIM-3 by dendritic cells, TIM-3 inhibits the antitumor efficacy of DNA vaccines and chemotherapy by binding to the damage-associated molecular pattern molecule, HMGB1.

Galectin-9 increases Tim-3+ dendritic cells and CD8+ T cells and enhances antitumor immunity via galectin-9-Tim-3 interactions

A Tim-3 ligand, galectin-9 (Gal-9), modulates various functions of innate and adaptive immune responses. In this study, we demonstrate that Gal-9 prolongs the survival of Meth-A tumor-bearing mice in a dose- and time-dependent manner. Although Gal-9 did not prolong the survival of tumor-bearing nude mice, transfer of naive spleen cells restored a prolonged Gal-9-induced survival in nude mice, indicating possible involvement of T cell-mediated immune responses in Gal-9-mediated antitumor activity. Gal-9 administration increased the number of IFN-gamma-producing Tim-3(+) CD8(+) T cells with enhanced granzyme B and perforin expression, although it induced CD4(+) T cell apoptosis. It simultaneously increased the number of Tim-3(+)CD86(+) mature dendritic cells (DCs) in vivo and in vitro. Coculture of CD8(+) T cells with DCs from Gal-9-treated mice increased the number of IFN-gamma producing cells and IFN-gamma production. Depletion of Tim-3(+) DCs from DCs of Gal-9-treated tumor-bearing mice decreased the number of IFN-gamma-producing CD8(+) T cells. Such DC activity was significantly abrogated by Tim-3-Ig, suggesting that Gal-9 potentiates CD8(+) T cell-mediated antitumor immunity via Gal-9-Tim-3 interactions between DCs and CD8(+) T cells.