Diminished Innate Antiviral Response to Adenovirus Vectors in cGAS/STING-Deficient Mice Minimally Impacts Adaptive Immunity

Adenoviral Vector System: A Comprehensive Overview of Constructions, Therapeutic Applications and Host Responses

Adenoviral vectors are crucial for gene therapy and vaccine development, offering a platform for gene delivery into host cells. Since the discovery of adenoviruses, first-generation vectors with limited capacity have evolved to third-generation vectors flacking viral coding sequences, balancing safety and gene-carrying capacity. The applications of adenoviral vectors for gene therapy and anti-viral treatments have expanded through the use of in vitro ligation and homologous recombination, along with gene editing advancements such as CRISPR-Cas9. Current research aims to maintain the efficacy and safety of adenoviral vectors by addressing challenges such as pre-existing immunity against adenoviral vectors and developing new adenoviral vectors from rare adenovirus types and non-human species. In summary, adenoviral vectors have great potential in gene therapy and vaccine development. Through continuous research and technological advancements, these vectors are expected to lead to the development of safer and more effective treatments.

cGAS-STING, an important signaling pathway in diseases and their therapy

Since cyclic guanosine monophosphate-adenosine monophosphate synthase (cGAS)-stimulator of interferon genes (STING) signaling pathway was discovered in 2013, great progress has been made to elucidate the origin, function, and regulating mechanism of cGAS-STING signaling pathway in the past decade. Meanwhile, the triggering and transduction mechanisms have been continuously illuminated. cGAS-STING plays a key role in human diseases, particularly DNA-triggered inflammatory diseases, making it a potentially effective therapeutic target for inflammation-related diseases. Here, we aim to summarize the ancient origin of the cGAS-STING defense mechanism, as well as the triggers, transduction, and regulating mechanisms of the cGAS-STING. We will also focus on the important roles of cGAS-STING signal under pathological conditions, such as infections, cancers, autoimmune diseases, neurological diseases, and visceral inflammations, and review the progress in drug development targeting cGAS-STING signaling pathway. The main directions and potential obstacles in the regulating mechanism research and therapeutic drug development of the cGAS-STING signaling pathway for inflammatory diseases and cancers will be discussed. These research advancements expand our understanding of cGAS-STING, provide a theoretical basis for further exploration of the roles of cGAS-STING in diseases, and open up new strategies for targeting cGAS-STING as a promising therapeutic intervention in multiple diseases.

Drosophila melanogaster Sting mediates Coxiella burnetii infection by reducing accumulation of reactive oxygen species

The Gram-negative bacterium Coxiella burnetii is the causative agent of query fever in humans and coxiellosis in livestock. C. burnetii infects a variety of cell types, tissues, and animal species including mammals and arthropods, but there is much left to be understood about the molecular mechanisms at play during infection in distinct species. Human stimulator of interferon genes (STING) induces an innate immune response through the induction of type I interferons (IFNs), and IFN promotes or suppresses C. burnetii replication, depending on tissue type. Drosophila melanogaster contains a functional STING ortholog (Sting) which activates NF-κB signaling and autophagy. Here, we sought to address the role of D. melanogaster Sting during C. burnetii infection to uncover how Sting regulates C. burnetii infection in flies. We show that Sting-null flies exhibit higher mortality and reduced induction of antimicrobial peptides following C. burnetii infection compared to control flies. Additionally, Sting-null flies induce lower levels of oxidative stress genes during infection, but the provision of N-acetyl-cysteine (NAC) in food rescues Sting-null host survival. Lastly, we find that reactive oxygen species levels during C. burnetii infection are higher in Drosophila S2 cells knocked down for Sting compared to control cells. Our results show that at the host level, NAC provides protection against C. burnetii infection in the absence of Sting, thus establishing a role for Sting in protection against oxidative stress during C. burnetii infection.

cGAS: action in the nucleus

As a canonical cytoplasmic DNA sensor, cyclic GMP-AMP synthase (cGAS) plays a key role in innate immunity. In recent years, a growing number of studies have shown that cGAS can also be located in the nucleus and plays new functions such as regulating DNA damage repair, nuclear membrane repair, chromosome fusion, DNA replication, angiogenesis and other non-canonical functions. Meanwhile, the mechanisms underlying the nucleo-cytoplasmic transport and the regulation of cGAS activation have been revealed in recent years. Based on the current understanding of the structure, subcellular localization and canonical functions of cGAS, this review focuses on summarizing the mechanisms underlying nucleo-cytoplasmic transport, activity regulation and non-canonical functions of cGAS in the nucleus. We aim to provide insights into exploring the new functions of cGAS in the nucleus and advance its clinical translation.

SOCS3 inhibiting JAK-STAT pathway enhances oncolytic adenovirus efficacy by potentiating viral replication and T-cell activation

Oncolytic viruses (OVs) are emerging as a potentially useful treatment for malignancies due to the capabilities of direct oncolysis and immune induction. Improving the replication of OVs is an effective approach to enhance the oncolytic effects. Here, we observed that cancer cells with deficiencies in JAK-STAT pathway showed greater sensitivity to oncolytic adenovirus (oAd), and JAK inhibitor could enhance the replication of oAd. Therefore, we constructed a novel oAd expressing SOCS3, a major negative regulator of JAK-STAT pathway, and confirmed that oAd-SOCS3 exhibited a more significant antitumor effect than oAd-Ctrl both in vitro and in vivo. Mechanistically, SOCS3 inhibited the activation of JAK-STAT pathway, resulting in stronger tumor selective replication of oAd and downregulated expression of PD-L1 on cancer cells as well. Both benefits could collectively awaken antitumor immunity. This study highlights the importance of JAK-STAT pathway in viral replication and confirms the treatment of oAd-SOCS3 in potential clinical applications.

Two Novel Adenovirus Vectors Mediated Differential Antibody Responses via Interferon-α and Natural Killer Cells

Recombinant adenovirus vectors have been widely used in vaccine development. To overcome the preexisting immunity of human adenovirus type 5 (Ad5) in populations, a range of chimpanzee or rare human adenovirus vectors have been generated. However, these novel adenovirus vectors mediate the diverse immune responses in the hosts. In this study, we explored the immune mechanism of differential antibody responses to SARS-CoV-2 S protein in mice immunized by our previously developed two novel simian adenovirus type 23 (Sad23L) and human adenovirus type 49 (Ad49L), and Ad5 vectored COVID-19 vaccines. Sad23L-nCoV-S and Ad5-nCoV-S vaccines induced the low level of interferon-α (IFN-α) and the high level of antigen-specific antibody responses in wild-type and IFN-α/β receptor defective (IFNAR-/-) C57 mice, while Ad49L-nCoV-S vaccine induced the high IFN-α and low antibody responses in C57 mice but the high antibody response in IFNAR-/- mice. In addition, the high antibody response was detected in natural killer (NK) cells-blocked but the low in follicular helper T (TFH) cells -blocked C57 mice immunized with Ad49L-nCoV-S vaccine. These results showed that Ad49L vectored vaccine stimulated IFN-α secretion to activate NK cells, and then reduced the number of TFH cells, generation center (GC) B cells and plasma cells, and subsequently reduced antigen-specific antibody production. The different novel adenovirus vectors could be selected for vaccine development according to the need for either humoral or cellular or both immune protections against a particular disease. IMPORTANCE Novel adenovirus vectors are an important antigen delivery platform for vaccine development. Understanding the immune diversity between different adenoviral vectors is critical to design the proper vaccine against an aim disease. In this study, we described the immune mechanism of Sad23L and Ad49L vectored vaccines for raising the equally high specific T cell response but the different level of specific antibody responses in mice. We found that Ad49L-vectored vaccine initiated the high IFN-α and activated NK cells to inhibit antibody response via downregulating the number of CD4+ TFH cells leading to the decline of GC B cells and plasma cells.

The Oncolytic Adenovirus XVir-N-31, in Combination with the Blockade of the PD-1/PD-L1 Axis, Conveys Abscopal Effects in a Humanized Glioblastoma Mouse Model

Glioblastoma (GBM) is an obligatory lethal brain tumor with a median survival, even with the best standard of care therapy, of less than 20 months. In light of this fact, the evaluation of new GBM treatment approaches such as oncolytic virotherapy (OVT) is urgently needed. Based on our preliminary preclinical data, the YB-1 dependent oncolytic adenovirus (OAV) XVir-N-31 represents a promising therapeutic agent to treat, in particular, therapy resistant GBM. Preclinical studies have shown that XVir-N-31 prolonged the survival of GBM bearing mice. Now using an immunohumanized mouse model, we examined the immunostimulatory effects of XVir-N-31 in comparison to the wildtype adenovirus (Ad-WT). Additionally, we combined OVT with the inhibition of immune checkpoint proteins by using XVir-N-31 in combination with nivolumab, or by using a derivate of XVir-N-31 that expresses a PD-L1 neutralizing antibody. Although in vitro cell killing was higher for Ad-WT, XVir-N-31 induced a much stronger immunogenic cell death that was further elevated by blocking PD-1 or PD-L1. In vivo, an intratumoral injection of XVir-N-31 increased tumor infiltrating lymphocytes (TILs) and NK cells significantly more than Ad-WT not only in the virus-injected tumors, but also in the untreated tumors growing in the contralateral hemisphere. This suggests that for an effective treatment of GBM, immune activating properties by OAVs seem to be of greater importance than their oncolytic capacity. Furthermore, the addition of immune checkpoint inhibition (ICI) to OVT further induced lymphocyte infiltration. Consequently, a significant reduction in contralateral non-virus-injected tumors was only visible if OVT was combined with ICI. This strongly indicates that for an effective eradication of GBM cells that cannot be directly targeted by an intratumoral OV injection, additional ICI therapy is required.

STING-pathway modulation to enhance the immunogenicity of adenoviral-vectored vaccines

Traditional chemical adjuvants remain a practical means of enhancing the immunogenicity of vaccines. Nevertheless, it is recognized that increasing the immunogenicity of viral vectors is challenging. Recently, STING ligands have been shown to enhance the efficacy of different vaccine platforms, but their affectivity on viral-vectored vaccination has not been fully assessed. In this study we used a multi-pronged approach to shed light on the immunological properties and potential mechanisms of action of this type of adjuvant and focused our study on replication-deficient human adenovirus serotype 5 (AdHu5). When the STING ligand 2'3'-cGAMP was mixed with AdHu5, the adjuvant enhanced anti-vector immune responses while decreasing the transgene-specific CD8+ T cell response. Studies employing STING-knockout mice and a 2'3'-cGAMP inactive analogue confirmed the aforementioned effects were STING dependent. In vitro assays demonstrated 2'3'-cGAMP induced the production of IFN-β which in turn negatively affected AdHu5 transgene expression and CD8+ T cell immunogenicity. In an effort to overcome the negative impact of early 2'3'-cGAMP signaling on AdHu5 transgene immunogenicity, we generated a bicistronic vector encoding the 2'3'-cGAMP together with a model antigen. Intracellular production of 2'3'-cGAMP after AdHu5 infection was able to enhance transgene-specific CD8+ T cell immunogenicity, although not to a level that would warrant progression of this adjuvant to clinical assessment. This work highlights the importance of timing of 2'3'-cGAMP administration when assessing its adjuvant capacity with different vaccine modalities.

Instructing durable humoral immunity for COVID-19 and other vaccinable diseases

Many aspects of SARS-CoV-2 have fully conformed with the principles established by decades of viral immunology research, ultimately leading to the crowning achievement of highly effective COVID-19 vaccines. Nonetheless, the pandemic has also exposed areas where our fundamental knowledge is thinner. Some key unknowns are the duration of humoral immunity post-primary infection or vaccination and how long booster shots confer protection. As a corollary, if protection does not last as long as desired, what are some ways it can be improved? Here, I discuss lessons from other infections and vaccines that point to several key features that influence durable antibody production and the perseverance of immunity. These include (1) the specific innate sensors that are initially triggered, (2) the kinetics of antigen delivery and persistence, (3) the starting B cell receptor (BCR) avidity and antigen valency, and (4) the memory B cell subsets that are recalled by boosters. I further highlight the fundamental B cell-intrinsic and B cell-extrinsic pathways that, if understood better, would provide a rational framework for vaccines to reliably provide durable immunity.

Engaging Pattern Recognition Receptors in Solid Tumors to Generate Systemic Antitumor Immunity

Malignant tumors frequently exploit innate immunity to evade immune surveillance. The priming, function, and polarization of antitumor immunity fundamentally depends upon context provided by the innate immune system, particularly antigen presenting cells. Such context is determined in large part by sensing of pathogen specific and damage associated features by pathogen recognition receptors (PRRs). PRR activation induces the delivery of T cell priming cues (e.g. chemokines, co-stimulatory ligands, and cytokines) from antigen presenting cells, playing a decisive role in the cancer immunity cycle. Indeed, endogenous PRR activation within the tumor microenvironment (TME) has been shown to generate spontaneous antitumor T cell immunity, e.g., cGAS-STING mediated activation of antigen presenting cells after release of DNA from dying tumor cells. Thus, instigating intratumor PRR activation, particularly with the goal of generating Th1-promoting inflammation that stokes endogenous priming of antitumor CD8⁺ T cells, is a growing area of clinical investigation. This approach is analogous to in situ vaccination, ultimately providing a personalized antitumor response against relevant tumor associated antigens. Here I discuss clinical stage intratumor modalities that function via activation of PRRs. These approaches are being tested in various solid tumor contexts including melanoma, colorectal cancer, glioblastoma, head and neck squamous cell carcinoma, bladder cancer, and pancreatic cancer. Their mechanism (s) of action relative to other immunotherapy approaches (e.g., antigen-defined cancer vaccines, CAR T cells, dendritic cell vaccines, and immune checkpoint blockade), as well as their potential to complement these approaches are also discussed. Examples to be reviewed include TLR agonists, STING agonists, RIG-I agonists, and attenuated or engineered viruses and bacterium. I also review common key requirements for effective in situ immune activation, discuss differences between various strategies inclusive of mechanisms that may ultimately limit or preclude antitumor efficacy, and provide a summary of relevant clinical data.

Cytokine Responses to Adenovirus and Adenovirus Vectors

The expression of cytokines and chemokines in response to adenovirus infection is tightly regulated by the innate immune system. Cytokine-mediated toxicity and cytokine storm are known clinical phenomena observed following naturally disseminated adenovirus infection in immunocompromised hosts as well as when extremely high doses of adenovirus vectors are injected intravenously. This dose-dependent, cytokine-mediated toxicity compromises the safety of adenovirus-based vectors and represents a critical problem, limiting their utility for gene therapy applications and the therapy of disseminated cancer, where intravenous injection of adenovirus vectors may provide therapeutic benefits. The mechanisms triggering severe cytokine response are not sufficiently understood, prompting efforts to further investigate this phenomenon, especially in clinically relevant settings. In this review, we summarize the current knowledge on cytokine and chemokine activation in response to adenovirus- and adenovirus-based vectors and discuss the underlying mechanisms that may trigger acute cytokine storm syndrome. First, we review profiles of cytokines and chemokines that are activated in response to adenovirus infection initiated via different routes. Second, we discuss the molecular mechanisms that lead to cytokine and chemokine transcriptional activation. We further highlight how immune cell types in different organs contribute to synthesis and systemic release of cytokines and chemokines in response to adenovirus sensing. Finally, we review host factors that can limit cytokine and chemokine expression and discuss currently available and potential future interventional approaches that allow for the mitigation of the severity of the cytokine storm syndrome. Effective cytokine-targeted interventional approaches may improve the safety of systemic adenovirus delivery and thus broaden the potential clinical utility of adenovirus-based therapeutic vectors.

Cell Type-Specific Roles of STAT3 Signaling in the Pathogenesis and Progression of K-ras Mutant Lung Adenocarcinoma

Simple Summary

Lung adenocarcinomas with mutations in the K-ras gene are hard to target pharmacologically and highly lethal. As a result, there is a need to identify other therapeutic targets that influence K-ras oncogenesis. One contender is STAT3, a transcription factor that is associated with K-ras mutations and aids tumor development and progression through tumor cell intrinsic and extrinsic mechanisms. In this review, we summarize the lung epithelial and infiltrating immune cells that express STAT3, the roles of STAT3 in K-ras mutant lung adenocarcinoma, and therapies that may be able to target STAT3.

Abstract

Worldwide, lung cancer, particularly K-ras mutant lung adenocarcinoma (KM-LUAD), is the leading cause of cancer mortality because of its high incidence and low cure rate. To treat and prevent KM-LUAD, there is an urgent unmet need for alternative strategies targeting downstream effectors of K-ras and/or its cooperating pathways. Tumor-promoting inflammation, an enabling hallmark of cancer, strongly participates in the development and progression of KM-LUAD. However, our knowledge of the dynamic inflammatory mechanisms, immunomodulatory pathways, and cell-specific molecular signals mediating K-ras-induced lung tumorigenesis is substantially deficient. Nevertheless, within this signaling complexity, an inflammatory pathway is emerging as a druggable target: signal transducer and activator of transcription 3 (STAT3). Here, we review the cell type-specific functions of STAT3 in the pathogenesis and progression of KM-LUAD that could serve as a new target for personalized preventive and therapeutic intervention for this intractable form of lung cancer.

Nanodelivery of STING agonists against cancer and infectious diseases

Vaccination is a modality that has been widely explored for the treatment of various diseases. To increase the potency of vaccine formulations, immunostimulatory adjuvants have been regularly exploited, and the stimulator of interferon genes (STING) signaling pathway has recently emerged as a remarkable therapeutic target. STING is an endogenous protein on the endoplasmic reticulum that is a downstream sensor to cytosolic DNA. Upon activation, STING initiates a series of intracellular signaling cascades that ultimately generate potent type I interferon-mediated immune responses. Both natural and synthetic agonists have been used to stimulate the STING pathway, but they are usually administered locally due to low bioavailability, instability, and difficulty in bypassing the plasma membrane. With excellent pharmacokinetic profiles and versatility, nanocarriers can address many of these challenges and broaden the application of STING vaccines. Along these lines, STING-inducing nanovaccines are being developed to address a wide range of diseases. In this review, we discuss the recent advances in STING nanovaccines for anticancer, antiviral, and antibacterial applications.

Adenovirus vector-based vaccine for infectious diseases

Replication-incompetent adenovirus (Ad) vectors have been widely used as gene delivery vehicles in both gene therapy studies and basic studies for gene function analysis due to their highly advantageous properties, which include high transduction efficiencies, relatively large capacities for transgenes, and high titer production. In addition, Ad vectors induce moderate levels of innate immunity and have relatively high thermostability, making them very attractive as potential vaccine vectors. Accordingly, it is anticipated that Ad vectors will be used in vaccines for the prevention of infectious diseases, including Ebola virus disease and acquired immune deficiency syndrome (AIDS). Much attention is currently focused on the potential use of an Ad vector vaccine for coronavirus disease 2019 (COVID-19). In this review, we describe the basic properties of an Ad vector, Ad vector-induced innate immunity and immune responses to Ad vector-produced transgene products. Development of novel Ad vectors which can overcome the drawbacks of conventional Ad vector vaccines and clinical application of Ad vector vaccines to several infectious diseases are also discussed.

Human IFIT3 Protein Induces Interferon Signaling and Inhibits Adenovirus Immediate Early Gene Expression

Interferons (IFNs) are one of the hallmarks of host antiviral immunity. IFNs exert their antiviral activities through the induction of IFN-stimulated genes (ISGs) and antiviral proteins; however, the mechanism by which ISGs inhibit adenovirus (Ad) replication is not clearly understood. IFNs repress Ad immediate early gene expression and, consequently, all subsequent aspects of the viral life cycle. In this study, we found that IFN-induced protein with tetratricopeptide repeats 3, IFIT3 (ISG60), restricts Ad replication. IFIT3 repressed Ad E1A immediate early gene expression but did not alter Ad genome entry into the nucleus. Expression of IFIT3 led to phosphorylation of TBK1, IRF3, and STAT1; increased expression of IFNβ and ISGs; and required IFIT1 and IFIT2 partner proteins. During RNA virus infections, it is known that IFIT3 stimulates IFN production through mitochondrial antiviral signaling (MAVS)-mediated activation of TBK1 which synergizes activation of IRF3 and NF-κB. MAVS or TBK1 depletion in cells expressing IFIT3 blocked IFN signaling and reversed the Ad replication restriction. In addition, STING depletion phenocopied the effect suggesting that IFIT3 activates the STING pathway with cross talk to the MAVS pathway. This occurs independently of viral pathogen-associated molecular patterns (PAMPs). These results demonstrate that the expression of a single ISG, IFIT3, activates IFN signaling and establishes a cellular antiviral state independent of viral PAMPs. IMPORTANCE IFITs belong to a family of IFN-induced proteins that have broad antiviral functions, primarily studied with RNA viruses leaving a gap of knowledge on the effects of these proteins on DNA viruses. In this study we show that IFIT3, with its partner proteins IFIT1 and IFIT2, specifically restricts replication of human Ad, a DNA virus, by stimulating IFNβ production via the STING and MAVS pathways. This effect enhanced the IFN response and is independent of viral PAMPs. These results reveal a novel mechanism of activation of IFN signaling to enhance cellular antiviral responses.

Delivery of Anti-IFNAR1 shRNA to Hepatic Cells Decreases IFNAR1 Gene Expression and Improves Adenoviral Transduction and Transgene Expression

Chronic liver injury leads to advanced fibrosis, cirrhosis, and hepatocellular carcinoma. Genetical cell treatment related to the use of adenovirus (Ads) has proven to be beneficial and efficient in the recovery of hepatic diseases. Nevertheless, they are highly immunogenic and trigger an immune response where interferons type 1 (IFN-I) play a very important role. Three shRNAs against the Interferon-1 receptor (IFNAR1) were designed and cloned in pENTR/U6 plasmid and amplified in DH5α cells. Huh7 cells were transfected with these plasmids in the presence or absence of 1 × 10⁹ viral particles/ml of adenovirus containing the green fluorescent protein gene used as a reporter. Transfection with the shRNA plasmids partially inhibited the IFNAR1 expression. This inhibition substantially decreased antiviral response, demonstrated by the decrease of IFNAR1, IFN-α, and TNF-α gene expression, and the decrease at protein levels of IFNAR1, Protein kinase RNA-activated (PKR), and phosphorylated STAT1, allowing higher adenoviral transduction and transgene expression. Interestingly it was seen shRNA inhibited macrophage activation. These results suggest that the inhibition of the IFN-I pathway could be a strategy to minimize the immune response against Adenoviral vectors allowing higher Adenovirus transduction extending the transgene expression.

cGAS-STING-mediated sensing pathways in DNA and RNA virus infections: crosstalk with other sensing pathways

Viruses cause a variety of diseases in humans and other organisms. The most important defense mechanism against viral infections is initiated when the viral genome is sensed by host proteins, and this results in interferon production and pro-inflammatory cytokine responses. The sensing of the viral genome or its replication intermediates within host cells is mediated by cytosolic proteins. For example, cGAS and IFI16 recognize non-self DNA, and RIG-I and MDA5 recognize non-self RNA. Once these sensors are activated, they trigger a cascade of reactions activating downstream molecules, which eventually results in the transcriptional activation of type I and III interferons, which play a critical role in suppressing viral propagation, either by directly limiting their replication or by inducing host cells to inhibit viral protein synthesis. The immune response against viruses relies solely upon sensing of viral genomes and their downstream signaling molecules. Although DNA and RNA viruses are sensed by distinct classes of receptor proteins, there is a possibility of overlap between the viral DNA and viral RNA sensing mechanisms. In this review, we focus on various host sensing molecules and discuss the associated signaling pathways that are activated in response to different viral infections. We further highlight the possibility of crosstalk between the cGAS-STING and the RIG-I-MAVS pathways to limit viral infections. This comprehensive review delineates the mechanisms by which different viruses evade host cellular responses to sustain within the host cells.

Nonhuman Adenoviral Vector-Based Platforms and Their Utility in Designing Next Generation of Vaccines for Infectious Diseases

Several human adenoviral (Ad) vectors have been developed for vaccine delivery owing to their numerous advantages, including the feasibility of different vector designs, the robustness of elicited immune responses, safety, and scalability. To expand the repertoire of Ad vectors for receptor usage and circumvention of Ad vector immunity, the use of less prevalent human Ad types or nonhuman Ads were explored for vector design. Notably, many nonhuman Ad vectors have shown great promise in preclinical and clinical studies as vectors for vaccine delivery. This review describes the key features of several nonhuman Ad vector platforms and their implications in developing effective vaccines against infectious diseases.

Inflammatory cytokine storms severity may be fueled by interactions of micronuclei and RNA viruses such as COVID-19 virus SARS-CoV-2. A hypothesis

In this review we bring together evidence that (i) RNA viruses are a cause of chromosomal instability and micronuclei (MN), (ii) those individuals with high levels of lymphocyte MN have a weakened immune response and are more susceptible to RNA virus infection and (iii) both RNA virus infection and MN formation can induce inflammatory cytokine production. Based on these observations we propose a hypothesis that those who harbor elevated frequencies of MN within their cells are more prone to RNA virus infection and are more likely, through combined effects of leakage of self-DNA from MN and RNA from viruses, to escalate pro-inflammatory cytokine production via the cyclic GMP-AMP synthase (cGAS), stimulator of interferon genes (STING) and the Senescence Associated Secretory Phenotype (SASP) mechanisms to an extent that is unresolvable and therefore confers high risk of causing tissue damage by an excessive and overtly toxic immune response. The corollaries from this hypothesis are (i) those with abnormally high MN frequency are more prone to infection by RNA viruses; (ii) the extent of cytokine production and pro-inflammatory response to infection by RNA viruses is enhanced and possibly exceeds threshold levels that may be unresolvable in those with elevated MN levels in affected organs; (iii) reduction of MN frequency by improving nutrition and life-style factors increases resistance to RNA virus infection and moderates inflammatory cytokine production to a level that is immunologically efficacious and survivable.

The role of cGAS-STING signalling in liver diseases

The recently identified novel cytosolic DNA sensor cyclic GMP-AMP synthase (cGAS) activates the downstream adaptor protein stimulator of interferon genes (STING) by catalysing the synthesis of cyclic GMP-AMP. This in turn initiates an innate immune response through the release of various cytokines, including type I interferon. Foreign DNA (microbial infection) or endogenous DNA (nuclear or mitochondrial leakage) can serve as cGAS ligands and lead to the activation of cGAS-STING signalling. Therefore, the cGAS-STING pathway plays essential roles in infectious diseases, sterile inflammation, tumours, and autoimmune diseases. In addition, cGAS-STING signalling affects the progression of liver inflammation through other mechanisms, such as autophagy and metabolism. In this review, we summarise recent advances in our understanding of the role of cGAS-STING signalling in the innate immune modulation of different liver diseases. Furthermore, we discuss the therapeutic potential of targeting the cGAS-STING pathway in the treatment of liver diseases.

Mitochondrial Regulation of Macrophage Response Against Pathogens

Innate immune cells play the first line of defense against pathogens. Phagocytosis or invasion by pathogens can affect mitochondrial metabolism in macrophages by diverse mechanisms and shape the macrophage response (proinflammatory vs. immunomodulatory) against pathogens. Besides β-nicotinamide adenine dinucleotide 2'-phosphate, reduced (NADPH) oxidase, mitochondrial electron transport chain complexes release superoxide for direct killing of the pathogen. Mitochondria that are injured are removed by mitophagy, and this process can be critical for regulating macrophage activation. For example, impaired mitophagy can result in cytosolic leakage of mitochondrial DNA (mtDNA) that can lead to activation of cGAS-STING signaling pathway of macrophage proinflammatory response. In this review, we will discuss how metabolism, mtDNA, mitophagy, and cGAS-STING pathway shape the macrophage response to infectious agents.

Efficient antitumor effects of a novel oncolytic adenovirus fully composed of species B adenovirus serotype 35

Oncolytic adenoviruses (OAds) are among the most promising oncolytic viruses. Almost all oncolytic adenoviruses are composed of human adenovirus serotype 5 (Ad5) (OAd5). However, expression of the primary infection receptor for Ad5, coxsackievirus-adenovirus receptor (CAR), often declines on malignant tumor cells, resulting in inefficient infection in CAR-negative tumor cells. In addition, at least 80% of adults have neutralizing antibodies against Ad5. In this study, we developed a novel OAd fully composed of OAd35. OAd35 recognizes CD46, which is ubiquitously expressed on almost all human cells and is often upregulated on malignant tumor cells, as an infection receptor. Moreover, 20% or fewer adults have neutralizing antibodies against Ad35. OAd35 mediated efficient cell lysis activities at levels similar to OAd5 in CAR-positive tumor cells, while OAd35 showed higher levels of cell lysis activities than OAd5 in CAR-negative tumor cells. Anti-Ad5 serum significantly inhibited in vitro tumor cell lysis activities of OAd5, whereas OAd35 exhibited comparable levels of in vitro tumor cell lysis activities in the presence of anti-Ad5 and naive serum. OAd35 significantly suppressed growth of the subcutaneous CAR-positive and CAR-negative tumors following intratumoral administration. These results indicated that OAd35 is a promising alternative oncolytic virus for OAd5.

Current Insights into the Host Immune Response to Respiratory Viral Infections

Respiratory viral infections often lead to severe illnesses varying from mild or asymptomatic upper respiratory tract infections to severe bronchiolitis and pneumonia or/and chronic obstructive pulmonary disease. Common viral infections, including but not limited to influenza virus, respiratory syncytial virus, rhinovirus and coronavirus, are often the leading cause of morbidity and mortality. Since the lungs are continuously exposed to foreign particles, including respiratory pathogens, it is also well equipped for recognition and antiviral defense utilizing the complex network of innate and adaptive immune cells. Immediately upon infection, a range of proinflammatory cytokines, chemokines and an interferon response is generated, thereby making the immune response a two edged sword, on one hand it is required to eliminate viral pathogens while on other hand it's prolonged response can lead to chronic infection and significant pulmonary damage. Since vaccines to all respiratory viruses are not available, a better understanding of the virus-host interactions, leading to the development of immune response, is critically needed to design effective therapies to limit the severity of inflammatory damage, enhance viral clearance and to compliment the current strategies targeting the virus. In this chapter, we discuss the host responses to common respiratory viral infections, the key players of adaptive and innate immunity and the fine balance that exists between the viral clearance and immune-mediated damage.

NLRP12 negatively regulates EtOH-induced liver macrophage activation via NF-κB pathway and mediates hepatocyte apoptosis in alcoholic liver injury

Alcohol-induced liver injury is characterized by abnormal liver dysfunction and excessive inflammation response. Recent years a wealth of data have been yielded indicating that EtOH (ethyl alcohol)-induced macrophage activation along with liver inflammation plays a dominating role in the progression of alcohol-induced liver injury. Here we found high expression of NLRP12 (Nucleotide-binding oligomerization domain protein 12, which is generally considered to be a negative regulator of inflammatory response) in EtOH-fed mouse liver tissue, primary Kupffer cells and EtOH-induced RAW264.7 cells. Additionally, overexpression of NLRP12 following Ad (adenovirus)-NLRP12-EGFP contributed to the attenuation of steatosis and inflammation in EtOH-fed mice model and EtOH-primed RAW264.7 cells. In parallel, Knockdown of NLRP12 aggravated the inflammatory response in RAW264.7 cells triggered by EtOH. Meanwhile, after administration of overexpression or inhibition of NLRP12 expression in vitro, the expression of phosphorylated protein of NF-kB signaling pathway was significantly affected. After increasing or decreasing the expression of NLRP12 in RAW264.7 cells, AML-12 cells were cultured with the supernatant of RAW264.7 cells stimulated by EtOH, and the percent of apoptosis ratio of AML-12 cells was remarkably altered. The study suggested that reduced inflammatory response induced by NLRP12-mediated inhibition of NF-kB pathway participated in the decrease of hepatocyte apoptosis in alcohol-induced liver injury. Collectively, these findings suggested the significance of NLRP12-mediated macrophage activation in alcohol-induced liver injury.

"Repair Me if You Can": Membrane Damage, Response, and Control from the Viral Perspective

Cells are constantly challenged by pathogens (bacteria, virus, and fungi), and protein aggregates or chemicals, which can provoke membrane damage at the plasma membrane or within the endo-lysosomal compartments. Detection of endo-lysosomal rupture depends on a family of sugar-binding lectins, known as galectins, which sense the abnormal exposure of glycans to the cytoplasm upon membrane damage. Galectins in conjunction with other factors orchestrate specific membrane damage responses such as the recruitment of the endosomal sorting complex required for transport (ESCRT) machinery to either repair damaged membranes or the activation of autophagy to remove membrane remnants. If not controlled, membrane damage causes the release of harmful components including protons, reactive oxygen species, or cathepsins that will elicit inflammation. In this review, we provide an overview of current knowledge on membrane damage and cellular responses. In particular, we focus on the endo-lysosomal damage triggered by non-enveloped viruses (such as adenovirus) and discuss viral strategies to control the cellular membrane damage response. Finally, we debate the link between autophagy and inflammation in this context and discuss the possibility that virus induced autophagy upon entry limits inflammation.

Factors Which Contribute to the Immunogenicity of Non-replicating Adenoviral Vectored Vaccines

Adenoviral vectors are a safe and potently immunogenic vaccine delivery platform. Non-replicating Ad vectors possess several attributes which make them attractive vaccines for infectious disease, including their capacity for high titer growth, ease of manipulation, safety, and immunogenicity in clinical studies, as well as their compatibility with clinical manufacturing and thermo-stabilization procedures. In general, Ad vectors are immunogenic vaccines, which elicit robust transgene antigen-specific cellular (namely CD8+ T cells) and/or humoral immune responses. A large number of adenoviruses isolated from humans and non-human primates, which have low seroprevalence in humans, have been vectorized and tested as vaccines in animal models and humans. However, a distinct hierarchy of immunological potency has been identified between diverse Ad vectors, which unfortunately limits the potential use of many vectors which have otherwise desirable manufacturing characteristics. The precise mechanistic factors which underlie the profound disparities in immunogenicity are not clearly defined and are the subject of ongoing, detailed investigation. It has been suggested that a combination of factors contribute to the potent immunogenicity of particular Ad vectors, including the magnitude and duration of vaccine antigen expression following immunization. Furthermore, the excessive induction of Type I interferons by some Ad vectors has been suggested to impair transgene expression levels, dampening subsequent immune responses. Therefore, the induction of balanced, but not excessive stimulation of innate signaling is optimal. Entry factor binding or receptor usage of distinct Ad vectors can also affect their in vivo tropism following administration by different routes. The abundance and accessibility of innate immune cells and/or antigen-presenting cells at the site of injection contributes to early innate immune responses to Ad vaccination, affecting the outcome of the adaptive immune response. Although a significant amount of information exists regarding the tropism determinants of the common human adenovirus type-5 vector, very little is known about the receptor usage and tropism of rare species or non-human Ad vectors. Increased understanding of how different facets of the host response to Ad vectors contribute to their immunological potency will be essential for the development of optimized and customized Ad vaccine platforms for specific diseases.

Immune Responses to Viral Gene Therapy Vectors

Several viral vector-based gene therapy drugs have now received marketing approval. A much larger number of additional viral vectors are in various stages of clinical trials for the treatment of genetic and acquired diseases, with many more in pre-clinical testing. Efficiency of gene transfer and ability to provide long-term therapy make these vector systems very attractive. In fact, viral vector gene therapy has been able to treat or even cure diseases for which there had been no or only suboptimal treatments. However, innate and adaptive immune responses to these vectors and their transgene products constitute substantial hurdles to clinical development and wider use in patients. This review provides an overview of the type of immune responses that have been documented in animal models and in humans who received gene transfer with one of three widely tested vector systems, namely adenoviral, lentiviral, or adeno-associated viral vectors. Particular emphasis is given to mechanisms leading to immune responses, efforts to reduce vector immunogenicity, and potential solutions to the problems. At the same time, we point out gaps in our knowledge that should to be filled and problems that need to be addressed going forward.

Lessons learned from adenovirus (1970-2019)

Animal viruses are well recognized for their ability to uncover fundamental cell and molecular processes, and adenovirus certainly provides a prime example. This review illustrates the lessons learned from studying adenovirus over the past five decades. We take a look back at the key studies of adenovirus structure and biophysical properties, which revealed the mechanisms of adenovirus association with antibody, cell receptor, and immune molecules that regulate infection. In addition, we discuss the critical contribution of studies of adenovirus gene expression to elucidation of fundamental reactions in pre-mRNA processing and its regulation. Other pioneering studies furnished the first examples of protein-primed initiation of DNA synthesis and viral small RNAs. As a nonenveloped virus, adenoviruses have furnished insights into the modes of virus attachment, entry, and penetration of host cells, and we discuss the diversity of cell receptors that support these processes, as well as membrane penetration. As a result of these extensive studies, adenovirus vectors were among the first to be developed for therapeutic applications. We highlight some of the early (unsuccessful) trials and the lessons learned from them.

STING signaling and host defense against microbial infection

The first line of host defense against infectious agents involves activation of innate immune signaling pathways that recognize specific pathogen-associated molecular patterns (PAMPs). Key triggers of innate immune signaling are now known to include microbial-specific nucleic acid, which is rapidly detected in the cytosol of the cell. For example, RIG-I-like receptors (RLRs) have evolved to detect viral RNA species and to activate the production of host defense molecules and cytokines that stimulate adaptive immune responses. In addition, host defense countermeasures, including the production of type I interferons (IFNs), can also be triggered by microbial DNA from bacteria, viruses and perhaps parasites and are regulated by the cytosolic sensor, stimulator of interferon genes (STING). STING-dependent signaling is initiated by cyclic dinucleotides (CDNs) generated by intracellular bacteria following infection. CDNs can also be synthesized by a cellular synthase, cGAS, following interaction with invasive cytosolic self-DNA or microbial DNA species. The importance of STING signaling in host defense is evident since numerous pathogens have developed strategies to prevent STING function. Here, we review the relevance of STING-controlled innate immune signaling in host defense against pathogen invasion, including microbial endeavors to subvert this critical process.

Innate immunity to adenovirus: lessons from mice

Adenovirus is a highly evolutionary successful pathogen, as it is widely prevalent across the animal kingdom, infecting hosts ranging from lizards and frogs to dolphins, birds, and humans. Although natural adenovirus infections in humans rarely cause severe pathology, intravenous injection of high doses of adenovirus-based vectors triggers rapid activation of the innate immune system, leading to cytokine storm syndrome, disseminated intravascular coagulation, thrombocytopenia, and hepatotoxicity, which individually or in combination may cause morbidity and mortality. Much of the information on exactly how adenovirus activates the innate immune system has been gathered from mouse experimental systems. Intravenous administration of adenovirus to mice revealed mechanistic insights into cellular and molecular components of the innate immunity that detect adenovirus particles, activate pro-inflammatory signaling pathways and cytokine production, sequester adenovirus particles from the bloodstream, and eliminate adenovirus-infected cells. Collectively, this information greatly improved our understanding of mechanisms of activation of innate immunity to adenovirus and may pave the way for designing safer adenovirus-based vectors for therapy of genetic and acquired human diseases.

The triggers of the cGAS-STING pathway and the connection with inflammatory and autoimmune diseases

Cyclic GMP-AMP synthase (cGAS) is a cytosolic nucleic acid sensor that can bind to dsDNA. It maintains an autoinhibited state in the absence of cytosolic dsDNA, while when activated, it in turn activates its adaptor protein STING, ultimately triggering a cascade that produces inflammatory cytokines and type I interferons (IFNs). With further research, additional types of nucleic acids have been found to be activators of the cGAS-STING pathway. The cGAS-STING pathway can provide protection or resistance against infections; however, improper or overactivation might cause severe inflammatory pathologies, including autoimmunity. This article systematically reviews the latest research progress on the axis, including categorical pathway triggers, the connection with autoimmune disease and drug therapy progress.

Adenovirus and Oxaliplatin cooperate as agnostic sensitizers for immunogenic cell death in colorectal carcinoma

Treatments with cytotoxic agents or viruses may cause Immunogenic Cell Death (ICD) that immunize tumor-bearing hosts but do not cause complete regression of tumor. We postulate that combining two ICD inducers may cause durable regression in immunocompetent mice. ICD was optimized in vitro by maximizing calreticulin externalization in human colorectal carcinoma (CRC) cells by exposure to mixtures of Oxaliplatin (OX) and human adenovirus (AdV). Six mm diameter CT26 or 4T1 carcinomas in flanks of BALB/c mice were injected once intratumorally (IT) with OX, AdV or their mixture. Tumor growth, Tumor-Infiltrating Lymphocytes (TIL), nodal cytotoxicity, and rejection of a viable cell challenge were measured. Tumors injected IT once with an optimum mixture of 80 µM OX - AdV 25 Multiplicity of Infection (MOI) in PBS buffer were 17-29% the volume of control tumors. When buffer was changed from PBS to 5% dextrose in water (D5W), volumes of tumors injected IT with 80 µM OX-AdV 25 MOI were 10% while IT OX or AdV alone were 32% and 40% the volume of IT buffer-treated tumors. OX-AdV IT increased CD3+ TIL by 4-fold, decreased CD8+ PD-1+ TIL from 79% to 19% and induced cytotoxicity to CT26 cells in draining node lymphocytes while lymphocytes from CT26-bearing untreated mice were not cytotoxic. OX-AdV IT in D5W caused complete regression in 40% of mice. Long-term survivors rejected a contralateral challenge of CT26. The buffer for Oxaliplatin is critical. The two ICD inducer mixture is promising as an agnostic sensitizer for carcinomas like colorectal carcinoma.

Diminished stimulator of interferon genes production with cigarette smoke-exposure contributes to weakened anti-adenovirus vectors response and destruction of lung in chronic obstructive pulmonary disease model

Cigarette smoke (CS) is the primary risk factor for chronic obstructive pulmonary disease (COPD) and dampens antiviral response, which increases viral infections and leads to COPD acute exacerbation (AECOPD). Adenovirus, a nonenveloped DNA virus, is linked with AECOPD, whose DNAs trigger innate immune response via interacting with pattern recognition receptors (PRRs). Stimulator of interferon genes (STING), as a cytosolic DNA sensor, participates in adenovirus-induced interferon β (IFNβ)-dependent antiviral response. STING is involved in various pulmonary diseases, but role of STING in pathogenesis of AECOPD is not well documented. In the present study, we explored relationship between STING and AECOPD induced by recombinant adenovirus vectors (rAdVs) and CS in wild type (WT) and STING-/- mice; and also characterized the inhibition of STING- IFNβ pathway in pulmonary epithelium exposed to cigarette smoke extract (CSE). We found that CS or CSE exposure alone dramatically inhibited STING expression, but not significantly effected IFNβ production. Moreover, CS or CSE-exposed significantly suppressed activation of STING-IFNβ pathway induced by rAdVs and suppressed clearance of rAdVs DNA. Inflammation, fibrosis and emphysema of lung tissues were exaggerated when treated with CS plus rAdVs, which further deteriorate in absences of STING. In A549 cells with knockdown of STING, we also observed enhancing apoptosis related to emphysema, especially CSE and adenovirus vectors in combination. Therefore, STING may play a protective role in preventing the progress of COPD.

The Role of Nucleic Acid Sensing in Controlling Microbial and Autoimmune Disorders

Innate immunity, the first line of defense against invading pathogens, is an ancient form of host defense found in all animals, from sponges to humans. During infection, innate immune receptors recognize conserved molecular patterns, such as microbial surface molecules, metabolites produces during infection, or nucleic acids of the microbe's genome. When initiated, the innate immune response activates a host defense program that leads to the synthesis proteins capable of pathogen killing. In mammals, the induction of cytokines during the innate immune response leads to the recruitment of professional immune cells to the site of infection, leading to an adaptive immune response. While a fully functional innate immune response is crucial for a proper host response and curbing microbial infection, if the innate immune response is dysfunctional and is activated in the absence of infection, autoinflammation and autoimmune disorders can develop. Therefore, it follows that the innate immune response must be tightly controlled to avoid an autoimmune response from host-derived molecules, yet still unencumbered to respond to infection. In this review, we will focus on the innate immune response activated from cytosolic nucleic acids, derived from the microbe or host itself. We will depict how viruses and bacteria activate these nucleic acid sensing pathways and their mechanisms to inhibit the pathways. We will also describe the autoinflammatory and autoimmune disorders that develop when these pathways are hyperactive. Finally, we will discuss gaps in knowledge with regard to innate immune response failure and identify where further research is needed.

Lung macrophage scavenger receptor SR-A6 (MARCO) is an adenovirus type-specific virus entry receptor

Macrophages are a diverse group of phagocytic cells acting in host protection against stress, injury, and pathogens. Here, we show that the scavenger receptor SR-A6 is an entry receptor for human adenoviruses in murine alveolar macrophage-like MPI cells, and important for production of type I interferon. Scavenger receptors contribute to the clearance of endogenous proteins, lipoproteins and pathogens. Knockout of SR-A6 in MPI cells, anti-SR-A6 antibody or the soluble extracellular SR-A6 domain reduced adenovirus type-C5 (HAdV-C5) binding and transduction. Expression of murine SR-A6, and to a lower extent human SR-A6 boosted virion binding to human cells and transduction. Virion clustering by soluble SR-A6 and proximity localization with SR-A6 on MPI cells suggested direct adenovirus interaction with SR-A6. Deletion of the negatively charged hypervariable region 1 (HVR1) of hexon reduced HAdV-C5 binding and transduction, implying that the viral ligand for SR-A6 is hexon. SR-A6 facilitated macrophage entry of HAdV-B35 and HAdV-D26, two important vectors for transduction of hematopoietic cells and human vaccination. The study highlights the importance of scavenger receptors in innate immunity against human viruses.

Macrophages are a diverse group of phagocytic cells acting in host protection against stress, injury, and pathogens. They phenotypically and functionally adapt to their local environment, for example, peritoneal macrophages are distinct from brain-resident microglia, from liver-resident Kupffer cells or lung macrophages in the lung. Airway macrophages are among the first cells to encounter human respiratory viruses, such as adenoviruses. They release pro-inflammatory cytokines, kill pathogens, present antigens, and restore tissues. Yet, interactions of viruses with lung macrophages are poorly understood, and it is unclear, how they lead to infection or virus clearance. Here we identified the murine scavenger receptor SR-A6 as a receptor for a subset of human adenoviruses on alveolar macrophage-like cells, so-called MPI cells. Scavenger receptors comprise a large family of trans-membrane proteins, and contribute to the clearance of endogenous proteins, lipoproteins and pathogens. In a series of robust experimentation, we show that adenoviruses use SR-A6 as an entry receptor for infection of MPI cells, and production of type I interferon. MPI cells are non-transformed, self-renewing macrophages derived from fetal murine liver, and closely resemble adult alveolar macrophages. The results demonstrate that SR-A6 binds virions on the surface of alveolar macrophage-like cells, and leads to infection.

Interaction between susceptibility loci in cGAS-STING pathway, MHC gene and HPV infection on the risk of cervical precancerous lesions in Chinese population

Human papillomavirus (HPV) infection is a definite risk factor for cervical cancer. Nevertheless, only some infected individuals actually develop cervical cancer. The cGAS-STING pathway in innate immunity plays an important role in protecting against HPV infection. Chen et al. described that the rs2516448 SNP in the MHC locus may affect susceptibility to cervical cancer, a finding that we attempted to replicate in a Chinese population. To investigate the effects of cGAS, STING and MHC polymorphisms on susceptibility to cervical precancerous lesions, 9 SNPs were analyzed in 164 cervical precancerous lesion cases and 428 controls. Gene-gene and gene-environment interactions were also evaluated. We found a significantly decreased risk of cervical precancerous lesions for the GG genotype of rs311678 in the cGAS gene (ORadjusted = 0.40, 95% CI: 0.16-0.98). Moreover, MDR analysis identified a significant three-locus interaction model, involving HPV infection, age at menarche and rs311678 in cGAS. Additionally, a significant antagonistic interaction between HPV infection and rs311678 was found on an additive scale. In conclusion, our results indicate that the rs311678 polymorphism in the cGAS gene confers genetic susceptibility to cervical precancerous lesions. Moreover, the three-way gene-environment interactions further demonstrate that the rs311678 polymorphism in cGAS can significantly decrease the risk of HPV infection and the elder at menarche.

WITHDRAWN: Research progress of cGAS-STING pathway in infectious diseases

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Stimulator of Interferon Genes Deficiency in Acute Exacerbation of Idiopathic Pulmonary Fibrosis

The stimulator of interferon genes (STING) is a key adaptor protein mediating innate immune defense against DNA viruses. To investigate the role of STING in acute exacerbation of idiopathic pulmonary fibrosis (AE-IPF), we isolated primary peripheral blood mononuclear cells (PBMCs) from patients and healthy controls (HCs). Raw264.7 and A549 cells were infected with herpes simplex virus type 1 (HSV-1). Mice with bleomycin-induced lung fibrosis were infected with HSV-1 to stimulate acute exacerbation of the lung fibrosis. Global gene expression profiling revealed a substantial downregulation of interferon-regulated genes (downstream of STING) in the AE-IPF group compared with the HC and stable IPF groups. The PBMCs of the AE-IPF group showed significantly reduced STING protein levels, increased levels of endoplasmic reticulum (ER) stress markers, and elevated apoptosis. HSV-1 infection decreased STING expression and stimulated the ER stress pathways in Raw264.7 and A549 cells in a time- and dose-dependent manner. HSV-1 infection exacerbated the bleomycin-induced lung injury in mice. In the primary bone marrow-derived macrophages of mice treated with bleomycin and HSV-1, STING protein expression was substantially reduced; ER stress was stimulated. Tauroursodeoxycholic acid, a known inhibitor of ER stress, partially reversed those HSV-1-mediated adverse effects in mice with bleomycin-induced lung injury. STING levels in PBMCs increased after treatment in patients showing improvement but remained at low levels in patients with deterioration. Viral infection may trigger ER stress, resulting in STING deficiency and AE-IPF onset.

cGAS-STING and Cancer: Dichotomous Roles in Tumor Immunity and Development

cGMP-AMP synthase (cGAS)-stimulator of interferon genes (STING) sensing has emerged as a key regulator of innate immune responses to both exogenous and endogenous DNA. Recent studies reveal critical roles for this pathway in natural antitumor immunity across cancer types as well as in immune checkpoint blockade therapy. However, it is also clear that some tumors evade cGAS-STING-mediated immune responses, and immunomodulatory therapeutics are currently being explored to target this pathway. Finally, we also discuss recent observations that cGAS-STING-mediated inflammation may promote tumor initiation, growth, and metastasis in certain malignancies and how this may complicate the utility of this pathway in therapeutic development.

Involvement of GATA1 and Sp3 in the activation of the murine STING gene promoter in NIH3T3 cells

Stimulator of Interferon Gene (STING) is a key mediator of innate immune signaling. STING plays a pivotal role in the pathogenesis of many diseases including infectious diseases, auto-immune diseases and cancer. Many studies have been carried out recently in the field of STING-regulated pathway, however, rarely of transcriptional mechanisms. To characterize the murine STING (mSTING) promoter, we cloned a series of different nucleotide sequences of the 5′-flanking region of the mSTING gene. Transient transfection of promoter-reporter recombinant plasmids and luciferase assay illustrated the region (−77/+177) relative to the transcription start site (TSS) of the mSTING gene was sufficient for full promoter activity. This region contains GATA1, IK2, Sp1/Sp3 and STAT putative transcription factor binding sites. Mutation of GATA1 or Sp1/Sp3 sites led to obvious decrease of the mSTING promoter activity. Overexpression of GATA1 and Sp3 enhanced the mSTING promoter activity, whereas knockdown of GATA1 and Sp3 by a siRNA strategy significantly reduced the transcription activity. Chromatin immunoprecipitation assays demonstrated that GATA1 and Sp3 interact with the mSTING promoter in vivo. These results provided the first analysis of mSTING promoter and demonstrated that transcription factor GATA1 and Sp3 positively regulate the basal transcription of the mSTING gene.

Cytosolic nucleic acid sensors and innate immune regulation

During viral and bacterial infections, pathogen-derived cytosolic nucleic acids are recognized by the intracellular RNA sensors retinoic acid-inducible gene I and melanoma-differentiated gene 5 and intracellular DNA sensors, including cyclic-di-GMP-AMP synthase, absent in melanoma 2, interferon (IFN)-gamma inducible protein 16, polymerase III, and so on. Binding of intracellular nucleic acids to these sensors activates downstream signaling cascades, resulting in the production of type I IFNs and pro-inflammatory cytokines to induce appropriate systematic immune responses. While these sensors also recognize endogenous nucleic acids and activate immune responses, they can discriminate between self- and non-self-nucleic acids. However, dysfunction of these sensors or failure of regulatory mechanisms causes aberrant activation of immune response and autoimmune disorders. In this review, we focus on how intracellular immune sensors recognize exogenous nucleic acids and activate the innate immune system, and furthermore, how autoimmune diseases result from dysfunction of these sensors.

Decreased expression of STING predicts poor prognosis in patients with gastric cancer

STING (stimulator of interferon genes) has recently been found to play an important role in host defenses against virus and intracellular bacteria via the regulation of type-I IFN signaling and innate immunity. Chronic infection with Helicobacter pylori is identified as the strongest risk factor for gastric cancer. Thus, we aim to explore the function of STING signaling in the development of gastric cancer. Immunohistochemistry was used to detect STING expression in 217 gastric cancer patients who underwent surgical resection. STING protein expression was remarkably decreased in tumor tissues compared to non-tumor tissues, and low STING staining intensity was positively correlated with tumor size, tumor invasion depth, lymph mode metastasis, TNM stage, and reduced patients’ survival. Multivariate analysis identified STING as an independent prognostic factor, which could improve the predictive accuracy for overall survival when incorporated into TNM staging system. In vitro studies revealed that knock-down of STING promoted colony formation, viability, migration and invasion of gastric cancer cells, and also led to a defect in cytosolic DNA sensing. Besides, chronic H. pylori infection up-regulated STING expression and activated STING signaling in mice. In conclusion, STING was proposed as a novel independent prognostic factor and potential immunotherapeutic target for gastric cancer.

MITA/STING and Its Alternative Splicing Isoform MRP Restrict Hepatitis B Virus Replication

An efficient clearance of hepatitis B virus (HBV) requires the coordinated work of both the innate and adaptive immune responses. MITA/STING, an adapter protein of the innate immune signaling pathways, plays a key role in regulating innate and adaptive immune responses to DNA virus infection. Previously, we identified an alternatively spliced isoform of MITA/STING, called MITA-related protein (MRP), and found that MRP could specifically block MITA-mediated interferon (IFN) induction while retaining the ability to activate NF-κB. Here, we asked whether MITA/STING and MRP were able to control the HBV replication. Both MITA/STING and MRP significantly inhibited HBV replication in vitro. MITA overexpression stimulated IRF3-IFN pathway; while MRP overexpression activated NF-κB pathway, suggesting these two isoforms may inhibit HBV replication through different ways. Using a hydrodynamic injection (HI) mouse model, we found that HBV replication was reduced following MITA/STING and MRP expression vectors in mice and was enhanced by the knockout of MITA/STING (MITA/STING^-/-). The HBV specific humoral and CD8⁺ T cell responses were impaired in MITA/STING deficient mice, suggesting the participation of MITA/STING in the initiation of host adaptive immune responses. In summary, our data suggest that MITA/STING and MRP contribute to HBV control via modulation of the innate and adaptive responses.

Decreased Expression of TMEM173 Predicts Poor Prognosis in Patients with Hepatocellular Carcinoma

Hepatocellular carcinoma (HCC) is one of the most lethal cancer types, and chronic infection with Hepatitis B Virus (HBV) is identified as the strongest risk factor for HCC. Transmembrane Protein 173 (TMEM173) is a pattern recognition receptor which functions as a major regulator of the innate immune response to viral and bacterial infections. However, the prognostic value of TMEM173 in HCC remains elusive. Thus, we aimed to evaluate the potential prognostic significance of TMEM173 expression in HCC patients following curative resection. Immunohistochemistry was used to detect TMEM173 expression in 96 HCC patients. We found that TMEM173 protein expression was remarkably decreased in tumor tissues compared to non-tumor tissues, and that TMEM173 staining intensity was inversely correlated with tumor size, tumor invasion TNM stage and overall survival (OS) in HCC patients. Multivariate analysis supported TMEM173 as an independent prognostic factor, and identified that combining TMEM173 expression with TNM stage showed better prognostic efficiency for OS in HCC patients. In summary, TMEM173 was discovered having an independent prognostic value and may serve as a potential immunotherapeutic target for HCC.

Adenovirus sensing by the immune system

The host immune system developed multiple ways for recognition of viral pathogens. Upon disseminated adenovirus infection, the immune system senses adenovirus invasion from the moment it enters the bloodstream. The soluble blood factors, FX, antibodies, and complement, can bind and activate plethora of host-protective immune responses. Adenovirus binding to the cellular β3 integrin and endosomal membrane rupture trigger activation of IL-1α/IL-1R1 proinflammatory cascade leading to attraction of cytotoxic immune cells to the site of infection. Upon cell entry, adenovirus exposes its DNA genome in the cytoplasm and triggers DNA sensors signaling. Even when inside the nucleus, the specialized cellular machinery that recognizes the double-strand DNA breaks become activated and triggers viral DNA replication arrest. Thus, the host employs very diverse mechanisms to prevent viral dissemination.