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

Peak transgene expression after intramuscular immunization of mice with adenovirus 26-based vector vaccines correlates with transgene-specific adaptive immune responses

Non-replicating adenovirus-based vectors have been broadly used for the development of prophylactic vaccines in humans and are licensed for COVID-19 and Ebola virus disease prevention. Adenovirus-based vectored vaccines encode for one or more disease specific transgenes with the aim to induce protective immunity against the target disease. The magnitude and duration of transgene expression of adenovirus 5- based vectors (human type C) in the host are key factors influencing antigen presentation and adaptive immune responses. Here we characterize the magnitude, duration, and organ biodistribution of transgene expression after single intramuscular administration of adenovirus 26-based vector vaccines in mice and evaluate the differences with adenovirus 5-based vector vaccine to understand if this is universally applicable across serotypes. We demonstrate a correlation between peak transgene expression early after adenovirus 26-based vaccination and transgene-specific cellular and humoral immune responses for a model antigen and SARS-CoV-2 spike protein, independent of innate immune activation. Notably, the memory immune response was similar in mice immunized with adenovirus 26-based vaccine and adenovirus 5-based vaccine, despite the latter inducing a higher peak of transgene expression early after immunization and a longer duration of transgene expression. Together these results provide further insights into the mode of action of adenovirus 26-based vector vaccines.

Type I Interferon, Induced by Adenovirus or Adenoviral Vector Infection, Regulates the Cytokine Response to Lipopolysaccharide in a Macrophage Type-Specific Manner

INTRODUCTION

While TLR ligands derived from microbial flora and pathogens are important activators of the innate immune system, a variety of factors such as intracellular bacteria, viruses, and parasites can induce a state of hyperreactivity, causing a dysregulated and potentially life-threatening cytokine over-response upon TLR ligand exposure. Type I interferon (IFN-αβ) is a central mediator in the induction of hypersensitivity and is strongly expressed in splenic conventional dendritic cells (cDC) and marginal zone macrophages (MZM) when mice are infected with adenovirus. This study investigates the ability of adenoviral infection to influence the activation state of the immune system and underlines the importance of considering this state when planning the treatment of patients.

METHODS

Infection with adenovirus-based vectors (Ad) or pretreatment with recombinant IFN-β was used as a model to study hypersensitivity to lipopolysaccharide (LPS) in mice, murine macrophages, and human blood samples. The TNF-α, IL-6, IFN-αβ, and IL-10 responses induced by LPS after pretreatment were measured. Mouse knockout models for MARCO, IFN-αβR, CD14, IRF3, and IRF7 were used to probe the mechanisms of the hypersensitive reaction.

RESULTS

We show that, similar to TNF-α and IL-6 but not IL-10, the induction of IFN-αβ by LPS increases strongly after Ad infection. This is true both in mice and in human blood samples ex vivo, suggesting that the regulatory mechanisms seen in the mouse are also present in humans. In mice, the scavenger receptor MARCO on IFN-αβ-producing cDC and splenic marginal zone macrophages is important for Ad uptake and subsequent cytokine overproduction by LPS. Interestingly, not all IFN-αβ-pretreated macrophage types exposed to LPS exhibit an enhanced TNF-α and IL-6 response. Pretreated alveolar macrophages and alveolar macrophage-like murine cell lines (MPI cells) show enhanced responses, while bone marrow-derived and peritoneal macrophages show a weaker response. This correlates with the respective absence or presence of the anti-inflammatory IL-10 response in these different macrophage types. In contrast, Ad or IFN-β pretreatment enhances the subsequent induction of IFN-αβ in all macrophage types. IRF3 is dispensable for the LPS-induced IFN-αβ overproduction in infected MPI cells and partly dispensable in infected mice, while IRF7 is required. The expression of the LPS co-receptor CD14 is important but not absolutely required for the elicitation of a TNF-α over-response to LPS in Ad-infected mice.

CONCLUSION

Viral infections or application of virus-based vaccines induces type I interferon and can tip the balance of the innate immune system in the direction of hyperreactivity to a subsequent exposure to TLR ligands. The adenoviral model presented here is one example of how multiple factors, both environmental and genetic, affect the physiological responses to pathogens. Being able to measure the current reactivity state of the immune system would have important benefits for infection-specific therapies and for the prevention of vaccination-elicited adverse effects.

Pathogenicity and virulence of human adenovirus F41: Possible links to severe hepatitis in children

Over 100 human adenoviruses (HAdVs) have been isolated and allocated to seven species, A-G. Species F comprises two members-HAdV-F40 and HAdV-F41. As their primary site of infection is the gastrointestinal tract they have been termed, with species A, enteric adenoviruses. HAdV-F40 and HAdV-F41 are a common cause of gastroenteritis and diarrhoea in children. Partly because of difficulties in propagating the viruses in the laboratory, due to their restrictions on growth in many cell lines, our knowledge of the properties of individual viral proteins is limited. However, the structure of HAdV-F41 has recently been determined by cryo-electron microscopy. The overall structure is similar to those of HAdV-C5 and HAdV-D26 although with some differences. The sequence and arrangement of the hexon hypervariable region 1 (HVR1) and the arrangement of the C-terminal region of protein IX differ. Variations in the penton base and hexon HVR1 may play a role in facilitating infection of intestinal cells by HAdV-F41. A unique feature of HAdV-F40 and F41, among human adenoviruses, is the presence and expression of two fibre genes, giving long and short fibre proteins. This may also contribute to the tropism of these viruses. HAdV-F41 has been linked to a recent outbreak of severe acute hepatitis "of unknown origin" in young children. Further investigation has shown a very high prevalence of adeno-associated virus-2 in the liver and/or plasma of some cohorts of patients. These observations have proved controversial as HAdV-F41 had not been reported to infect the liver and AAV-2 has generally been considered harmless.

Potent antitumor efficacy of human dental pulp stem cells armed with YSCH-01 oncolytic adenovirus

BACKGROUND

Systemic administration of oncolytic adenovirus for cancer therapy is still a challenge. Mesenchymal stem cells as cell carriers have gained increasing attention in drug delivery due to their excellent tumor tropism, immunosuppressive modulatory effects, and paracrine effects. However, the potential of human dental pulp stem cells (hDPSCs) loaded with oncolytic adenovirus for cancer biotherapy has not been investigated yet.

METHODS

The stemness of hDPSCs was characterized by FACS analysis and Alizarin red staining, Oil Red O staining, and immunofluorescence assays. The biological fitness of hDPSCs loaded with oncolytic adenovirus YSCH-01 was confirmed by virus infection with different dosages and cell viability CCK-8 assays. Additionally, the expression of CAR receptor in hDPSCs was detected by qPCR assay. Tumor tropism of hDPSC loaded with YSCH-01 in vitro and in vivo was investigated by Transwell assays and living tumor-bearing mice imaging technology and immunohistochemistry, Panoramic scanning of frozen section slices assay analysis. Furthermore, the antitumor efficacy was observed through the different routes of YSCH-01/hPDSCs administration in SW780 and SCC152 xenograft models. The direct tumor cell-killing effect of YSCH-01/hDPSCs in the co-culture system was studied, and the supernatant of YSCH-01/hDPSCs inhibited cell growth was further analyzed by CCK-8 assays.

RESULTS

hDPSCs were found to be susceptible to infection by a novel oncolytic adenovirus named YSCH-01 and were capable of transporting this virus to tumor sites at 1000 VP/cell infectious dosage in vitro and in vivo. Moreover, it was discovered that intraperitoneal injection of hDPSCs loaded with oncolytic adenovirus YSCH-01 exhibited potential anti-tumor effects in both SW780 and SCC152 xenograft models. The crucial role played by the supernatant secretome derived from hDPSCs loaded with YSCH-01 significantly exerted a specific anti-tumor effect without toxicity for normal cells, in both an active oncolytic virus and an exogenous protein-independent manner. Furthermore, the use of hDPSCs as a cell carrier significantly reduced the required dosage of virus delivery in vivo compared to other methods.

CONCLUSIONS

These findings highlight the promising clinical potential of hDPSCs as a novel cell carrier in the field of oncolytic virus-based anti-cancer therapy.

Atherosclerosis and Inflammation: Insights from the Theory of General Pathological Processes

Recent advances have greatly improved our understanding of the molecular mechanisms behind atherosclerosis pathogenesis. However, there is still a need to systematize this data from a general pathology perspective, particularly with regard to atherogenesis patterns in the context of both canonical and non-classical inflammation types. In this review, we analyze various typical phenomena and outcomes of cellular pro-inflammatory stress in atherosclerosis, as well as the role of endothelial dysfunction in local and systemic manifestations of low-grade inflammation. We also present the features of immune mechanisms in the development of productive inflammation in stable and unstable plaques, along with their similarities and differences compared to canonical inflammation. There are numerous factors that act as inducers of the inflammatory process in atherosclerosis, including vascular endothelium aging, metabolic dysfunctions, autoimmune, and in some cases, infectious damage factors. Life-critical complications of atherosclerosis, such as cardiogenic shock and severe strokes, are associated with the development of acute systemic hyperinflammation. Additionally, critical atherosclerotic ischemia of the lower extremities induces paracoagulation and the development of chronic systemic inflammation. Conversely, sepsis, other critical conditions, and severe systemic chronic diseases contribute to atherogenesis. In summary, atherosclerosis can be characterized as an independent form of inflammation, sharing similarities but also having fundamental differences from low-grade inflammation and various variants of canonical inflammation (classic vasculitis).

Cell entry and innate sensing shape adaptive immune responses to adenovirus-based vaccines

Nonreplicating adenovirus-based vectors have been successfully implemented as prophylactic vaccines against infectious viral diseases and induce protective cellular and humoral responses. Differences in the mechanisms of cellular entry or endosomal escape of these vectors contribute to differences in innate immune sensing between adenovirus species. Innate immune responses to adenovirus-based vaccines, such as interferon signaling, have been reported to affect the development of adaptive responses in preclinical studies, although limited data are available in humans. Understanding the mechanisms of these early events is critical for the development of vaccines that elicit effective and durable adaptive immune responses while maintaining an acceptable reactogenicity profile.

Persistent Antigen Harbored by Alveolar Macrophages Enhances the Maintenance of Lung-Resident Memory CD8+ T Cells

Lung tissue-resident memory T cells are crucial mediators of cellular immunity against respiratory viruses; however, their gradual decline hinders the development of T cell-based vaccines against respiratory pathogens. Recently, studies using adenovirus (Ad)-based vaccine vectors have shown that the number of protective lung-resident CD8+ TRMs can be maintained long term. In this article, we show that immunization of mice with a replication-deficient Ad serotype 5 expressing influenza (A/Puerto Rico/8/34) nucleoprotein (AdNP) generates a long-lived lung TRM pool that is transcriptionally indistinct from those generated during a primary influenza infection. In addition, we demonstrate that CD4+ T cells contribute to the long-term maintenance of AdNP-induced CD8+ TRMs. Using a lineage tracing approach, we identify alveolar macrophages as a cell source of persistent NP Ag after immunization with AdNP. Importantly, depletion of alveolar macrophages after AdNP immunization resulted in significantly reduced numbers of NP-specific CD8+ TRMs in the lungs and airways. Combined, our results provide further insight to the mechanisms governing the enhanced longevity of Ag-specific CD8+ lung TRMs observed after immunization with recombinant Ad.

Adenovirus entry: Stability, uncoating, and nuclear import

Adenoviruses (AdVs) are widespread in vertebrates. They infect the respiratory and gastrointestinal tracts, the eyes, heart, liver, and kidney, and are lethal to immunosuppressed people. Mastadenoviruses infecting mammals comprise several hundred different types, and many specifically infect humans. Human adenoviruses are the most widely used vectors in clinical applications, including cancer treatment and COVID-19 vaccination. AdV vectors are physically and genetically stable and generally safe in humans. The particles have an icosahedral coat and a nucleoprotein core with a DNA genome. We describe the concept of AdV cell entry and highlight recent advances in cytoplasmic transport, uncoating, and nuclear import of the viral DNA. We highlight a recently discovered "linchpin" function of the virion protein V ensuring cytoplasmic particle stability, which is relaxed at the nuclear pore complex by cues from the E3 ubiquitin ligase Mind bomb 1 (MIB1) and the proteasome triggering disruption. Capsid disruption by kinesin motor proteins and microtubules exposes the linchpin and renders protein V a target for MIB1 ubiquitination, which dissociates V from viral DNA and enhances DNA nuclear import. These advances uncover mechanisms controlling capsid stability and premature uncoating and provide insight into nuclear transport of nucleic acids.

Binding of adenovirus species C hexon to prothrombin and the influence of hexon on vector properties in vitro and in vivo

The majority of adenovirus (Ad) vectors are based on human Ad type 5, which is a member of Ad species C. Species C also includes the closely-related types 1, 2, 6, 57 and 89. It is known that coagulation factors bind to Ad5 hexon and play a key role in the liver tropism of Ad5 vectors, but it is unclear how coagulation factors affect vectors derived from other species C Ads. We evaluated species C Ad vectors both in vitro and following intravenous injection in mice. To assess the impact of hexon differences, we constructed chimeric Ad5 vectors that contain the hexon hypervariable regions from other species C types, including vectors with hexon mutations that decreased coagulation factor binding. After intravenous injection into mice, vectors with Ad5 or Ad6 hexon had strong liver tropism, while vectors with chimeric hexon from other Ad types had weaker liver tropism due to inhibition by natural antibodies and complement. In addition, we discovered a novel ability of hexon to bind prothrombin, which is the most abundant coagulation factor in blood, and we found striking differences in the affinity of Ads for human, mouse and bovine coagulation factors. When compared to Ad5, vectors with non-Ad5 species C hexons had considerably higher affinity for both human and mouse prothrombin. Most of the vectors tested were strongly dependent on coagulation factors for liver transduction, but vectors with chimeric Ad6 hexon showed much less dependence on coagulation factors than other vectors. We found that in vitro neutralization experiments with mouse serum predicted in vivo behavior of Ad5 vectors, but in vitro experiments did not predict the in vivo behavior of vectors based on other Ad types. In sum, hexons from different human Ad species C viruses confer diverse properties on vectors, including differing abilities to target the liver.

Hsp70 Inhibits the Replication of Fowl Adenovirus Serotype 4 by Suppressing Viral Hexon with the Assistance of DnaJC7

Fowl adenovirus serotype 4 (FAdV-4) infection results in serious hepatitis-hydropericardium syndrome (HHS) in broilers, which has caused great economic losses to the poultry industry; however, the specific host responses to FAdV-4 remain unknown. In this study, we identified 141 high-confidence protein-protein interactions (PPIs) between the main viral proteins (Hexon, Fiber 1, Fiber 2, and Penton bases) and host proteins via a liquid chromatography-tandem mass spectrometry (LC-MS/MS) assay. We found that heat shock protein 70 (Hsp70), the protein with the highest score, and its cofactor DnaJ heat shock protein 40 family member C7 (DnaJC7) could negatively regulate the replication of FAdV-4. Furthermore, the nucleotide binding domain (NBD) of Hsp70 and the J domain of DnaJC7 were necessary for inhibiting FAdV-4 replication. We verified that DnaJC7 as a bridge could bind to Hsp70 and Hexon, assisting the indirect interaction between Hsp70 and Hexon. In addition, we found that FAdV-4 infection strongly induced the expression of autophagy proteins and cellular Hsp70 in a dose-dependent manner. Blockage of Hexon by Hsp70 overexpression was significantly reduced when the autophagy pathway was blocked by the specific inhibitor chloroquine (CQ). Our results showed that Hsp70 was co-opted by DnaJC7 to interact with viral Hexon and inhibited Hexon through the autophagy pathway, leading to a considerable restriction of FAdV-4 replication. IMPORTANCE FAdV-4, as the main cause of HHS, has quickly spread all over the world in recent years, seriously threatening the poultry industry. The aim of this study was to identify the important host proteins that have the potential to regulate the life cycle of FAdV-4. We found that Hsp70 and DnaJC7 played crucial roles in regulating the amount of viral Hexon and extracellular viral titers. Moreover, we demonstrated that Hsp70 interacted with viral Hexon with the assistance of DnaJC7, followed by suppressing Hexon protein through the autophagy pathway. These results provide new insight into the role of the molecular chaperone complex Hsp70-DnaJC7 in FAdV-4 infection and suggest a novel strategy for anti-FAdV-4 drug development by targeting the specific interactions among Hsp70, DnaJC7 and Hexon.

Human Adenovirus Type 26 Infection Mediated by αvβ3 Integrin Is Caveolin-1-Dependent

Human adenovirus type 26 (HAdV26) has been recognized as a promising platform for vaccine vector development, and very recently vaccine against COVID-19 based on HAdV26 was authorized for emergency use. Nevertheless, basic biology of this virus, namely, pathway which HAdV26 uses to enter the cell, is still insufficiently known. We have shown here that HAdV26 infection of human epithelial cells expressing low amount of αvβ3 integrin involves clathrin and is caveolin-1-independent, while HAdV26 infection of cells with high amount of αvβ3 integrin does not involve clathrin but is caveolin-1-dependent. Thus, this study demonstrates that caveolin-1 is limiting factor in αvβ3 integrin-mediated HAdV26 infection. Regardless of αvβ3 integrin expression, HAdV26 infection involves dynamin-2. Our data provide for the first-time description of HAdV26 cell entry pathway, hence increase our knowledge of HAdV26 infection. Knowing that functionality of adenovirus vector is influenced by its cell entry pathway and intracellular trafficking, our results will contribute to better understanding of HAdV26 immunogenicity and antigen presentation when used as vaccine vector.

IMPORTANCE In order to fulfill its role as a vector, adenovirus needs to successfully deliver its DNA genome to the host nucleus, a process highly influenced by adenovirus intracellular translocation. Thus, cell entry pathway and intracellular trafficking determine functionality of human adenovirus-based vectors. Endocytosis of HAdV26, currently extensively studied as a vaccine vector, has not been described so far. We present here that HAdV26 infection of human epithelial cells with high expression of αvβ3 integrin, one of the putative HAdV26 receptors, is caveolin-1- and partially dynamin-2-dependent. Since caveolin containing domains provide a unique environment for specific signaling events and participate in inflammatory signaling one can imagine that directing HAdV26 cell entry toward caveolin-1-mediate pathway might play role in immunogenicity of this virus. Therefore, our results contribute to better understanding of HAdV26 infection pathway, hence, can be helpful in explaining induction of immune response and antigen presentation by HAdV26-based vaccine vector.

Adenovirus receptors on antigen-presenting cells of the skin

Skin, the largest human organ, is part of the first line of physical and immunological defense against many pathogens. Understanding how skin antigen-presenting cells (APCs) respond to viruses or virus-based vaccines is crucial to develop antiviral pharmaceutics, and efficient and safe vaccines. Here, we discuss the way resident and recruited skin APCs engage adenoviruses and the impact on innate immune responses. This article is protected by copyright. All rights reserved.

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.

Scavenger Receptors in the Pathogenesis of Viral Infections

Scavenger receptors (SR) are not only pattern recognition receptors involved in the immune response against pathogens but are also important receptors exploited by different virus to enter host cells, and thus represent targets for antiviral therapy. The high mutation rates of viruses, as well as their small genomes are partly responsible for the high rates of virus resistance and effective treatments remain a challenge. Most currently approved formulations target viral-encoded factors. Nevertheless, host proteins may function as additional targets. Thus, there is a need to explore and develop new strategies aiming at cellular factors involved in virus replication and host cell entry. SR-virus interactions have implications in the pathogenesis of several viral diseases and in adenovirus-based vaccination and gene transfer technologies, and may function as markers of severe progression. Inhibition of SR could reduce adenoviral uptake and improve gene therapy and vaccination, as well as reduce pathogenesis. In this review, we will examine the crucial role of SR play in cell entry of different types of human virus, which will allow us to further understand their role in protection and pathogenesis and its potential as antiviral molecules. The recent discovery of SR-B1 as co-factor of SARS-Cov-2 (severe acute respiratory syndrome coronavirus 2) entry is also discussed. Further fundamental research is essential to understand molecular interactions in the dynamic virus-host cell interplay through SR for rational design of therapeutic strategies.

Human adenovirus type 26 basic biology and its usage as vaccine vector

Due to their nature, adenoviruses have been recognised as promising candidates for vaccine vector development. Since they mimic natural infection, recombinant adenovirus vectors have been proven as ideal shuttles to deliver foreign transgenes aiming at inducing both humoral and cellular immune response. In addition, a potent adjuvant effect can be exerted due to the adenovirus inherent stimulation of various elements of innate and adaptive immunity. Due to its low seroprevalence in humans as well as induction of favourable immune response to inserted transgene, human adenovirus type 26 (HAdV-D26) has been recognised as a promising platform for vaccine vector development and is studied in number of completed or ongoing clinical studies. Very recently HAdV-D26 based Ebola and Covid-19 vaccines were approved for medical use. In this review, current state of the art regarding HAdV-D26 basic biology and its usage as vaccine vector will be discussed.

Characterization of scavenger receptor MARCO in orange-spotted grouper, Epinephelus coioides

Macrophage receptor with collagenous structure (MARCO) is a scavenger receptor that plays a crucial role in the immune response against microbial infections. To clarify the roles of fish MARCO in Singapore grouper iridovirus (SGIV) infection, we identified and characterized Ec-MARCO in the orange-spotted grouper (Epinephelus coioides). The Ec-MARCO encoded a 370-amino acid protein with transmembrane region, coiled coil region and SR domain, which shared high identities with reported MARCO. The abundant transcriptional level of Ec-MARCO was found in spleen, head kidney and blood. And the Ec-MARCO expression was significantly up-regulated in grouper spleen (GS) cells after infection with SGIV in vitro. Subcellular localization analysis revealed that Ec-MARCO was mainly distributed in the cytoplasm and on the cell membrane. Ec-MARCO knockdown in vitro significantly inhibited SGIV infection in GS cells, as evidenced by reduced decreased SGIV major capsid protein (MCP) transcription and MCP protein expression. Further studies showed that Ec-MARCO knockdown positively regulated proinflammatory cytokines and interferon-stimulated genes, and enhanced IFN and ISRE promoter activities. However, overexpression of Ec-MARCO did not affect SGIV entry into host cells. In summary, our results suggested that Ec-MARCO affected SGIV infection by regulating antiviral innate immune response.

Infection of non-cancer cells: A barrier or support for oncolytic virotherapy?

Oncolytic viruses are designed to specifically target cancer cells, sparing normal cells. Although numerous studies demonstrate the ability of oncolytic viruses to infect a wide range of non-tumor cells, the significance of this phenomenon for cancer virotherapy is poorly understood. To fill the gap, we summarize the data on infection of non-cancer targets by oncolytic viruses with a special focus on tumor microenvironment and secondary lymphoid tissues. The review aims to address two major questions: how do attenuated viruses manage to infect normal cells, and whether it is of importance for oncolytic virotherapy.

A viral ubiquitination switch attenuates innate immunity and triggers nuclear import of virion DNA and infection

Antiviral defense and virus exclusion from the cell nucleus restrict foreign nucleic acid influx and infection. How the genomes of DNA viruses evade cytosolic pattern recognition and cross the nuclear envelope is incompletely understood. Here, we show that the virion protein V of adenovirus functions as a linchpin between the genome and the capsid, thereby securing particle integrity. Absence of protein V destabilizes cytoplasmic particles and promotes premature genome release, raising cytokine levels through the DNA sensor cGAS. Non-ubiquitinable V yields stable virions, genome misdelivery to the cytoplasm, and increased cytokine levels. In contrast, normal protein V is ubiquitinated at the nuclear pore complex, dissociates from the virion depending on the E3 ubiquitin ligase Mib1 and the proteasome, and allows genome delivery into the nucleus for infection. Our data uncover previously unknown cellular and viral mechanisms of viral DNA nuclear import in pathogenesis, vaccination, gene therapy, and synthetic biology.

The RGD-binding integrins αvβ6 and αvβ8 are receptors for mouse adenovirus-1 and -3 infection

Mammalian adenoviruses (AdVs) comprise more than ~350 types including over 100 human (HAdVs) and just three mouse AdVs (MAdVs). While most HAdVs initiate infection by high affinity/avidity binding of their fiber knob (FK) protein to either coxsackievirus AdV receptor (CAR), CD46 or desmoglein (DSG)-2, MAdV-1 (M1) infection requires arginine-glycine-aspartate (RGD) binding integrins. To identify the receptors mediating MAdV infection we generated five novel reporter viruses for MAdV-1/-2/-3 (M1, M2, M3) transducing permissive murine (m) CMT-93 cells, but not B16 mouse melanoma cells expressing mCAR, human (h) CD46 or hDSG-2. Recombinant M1 or M3 FKs cross-blocked M1 and M3 but not M2 infections. Profiling of murine and human cells expressing RGD-binding integrins suggested that αvβ6 and αvβ8 heterodimers are associated with M1 and M3 infections. Ectopic expression of mβ6 in B16 cells strongly enhanced M1 and M3 binding, infection, and progeny production comparable with mαvβ6-positive CMT-93 cells, whereas mβ8 expressing cells were more permissive to M1 than M3. Anti-integrin antibodies potently blocked M1 and M3 binding and infection of CMT-93 cells and hαvβ8-positive M000216 cells. Soluble integrin αvβ6, and synthetic peptides containing the RGDLXXL sequence derived from FK-M1, FK-M3 and foot and mouth disease virus coat protein strongly interfered with M1/M3 infections, in agreement with high affinity interactions of FK-M1/FK-M3 with αvβ6/αvβ8, determined by surface plasmon resonance measurements. Molecular docking simulations of ternary complexes revealed a bent conformation of RGDLXXL-containing FK-M3 peptides on the subunit interface of αvβ6/β8, where the distal leucine residue dips into a hydrophobic pocket of β6/8, the arginine residue ionically engages αv aspartate215, and the aspartate residue coordinates a divalent cation in αvβ6/β8. Together, the RGDLXXL-bearing FKs are part of an essential mechanism for M1/M3 infection engaging murine and human αvβ6/8 integrins. These integrins are highly conserved in other mammals, and may favour cross-species virus transmission.

MARCO+ lymphatic endothelial cells sequester arthritogenic alphaviruses to limit viremia and viral dissemination

Viremia in the vertebrate host is a major determinant of arboviral reservoir competency, transmission efficiency, and disease severity. However, immune mechanisms that control arboviral viremia are poorly defined. Here, we identify critical roles for the scavenger receptor MARCO in controlling viremia during arthritogenic alphavirus infections in mice. Following subcutaneous inoculation, arthritogenic alphavirus particles drain via the lymph and are rapidly captured by MARCO+ lymphatic endothelial cells (LECs) in the draining lymph node (dLN), limiting viral spread to the bloodstream. Upon reaching the bloodstream, alphavirus particles are cleared from the circulation by MARCO-expressing Kupffer cells in the liver, limiting viremia and further viral dissemination. MARCO-mediated accumulation of alphavirus particles in the draining lymph node and liver is an important host defense mechanism as viremia and viral tissue burdens are elevated in MARCO-/- mice and disease is more severe. In contrast to prior studies implicating a key role for lymph node macrophages in limiting viral dissemination, these findings exemplify a previously unrecognized arbovirus-scavenging role for lymphatic endothelial cells and improve our mechanistic understanding of viremia control during arthritogenic alphavirus infection.

Virus Infection Variability by Single-Cell Profiling

Cell-to-cell variability of infection has long been known, yet it has remained one of the least understood phenomena in infection research. It impacts on disease onset and development, yet only recently underlying mechanisms have been studied in clonal cell cultures by single-virion immunofluorescence microscopy and flow cytometry. In this review, we showcase how single-cell RNA sequencing (scRNA-seq), single-molecule RNA-fluorescence in situ hybridization (FISH), and copper(I)-catalyzed azide-alkyne cycloaddition (click) with alkynyl-tagged viral genomes dissect infection variability in human and mouse cells. We show how the combined use of scRNA-FISH and click-chemistry reveals highly variable onsets of adenoviral gene expression, and how single live cell plaques reveal lytic and nonlytic adenovirus transmissions. The review highlights how scRNA-seq profiling and scRNA-FISH of coxsackie, influenza, dengue, zika, and herpes simplex virus infections uncover transcriptional variability, and how the host interferon response tunes influenza and sendai virus infections. We introduce the concept of "cell state" in infection variability, and conclude with advances by single-cell simultaneous measurements of chromatin accessibility and mRNA counts at high-throughput. Such technology will further dissect the sequence of events in virus infection and pathology, and better characterize the genetic and genomic stability of viruses, cell autonomous innate immune responses, and mechanisms of tissue injury.

Desmoglein 2 (DSG2) Is A Receptor of Human Adenovirus Type 55 Causing Adult Severe Community-Acquired Pneumonia

Human adenovirus type 55 (HAdV-B55) is a re-emergent acute respiratory disease pathogen that causes adult community-acquired pneumonia (CAP). Previous studies have shown that the receptor of HAdV-B14, which genome is highly similar with HAdV-B55, is human Desmoglein 2 (DSG2). However, whether the receptor of HAdV-B55 is DSG2 is undetermined because there are three amino acid mutations in the fiber gene between HAdV-B14 and HAdV-B55. Here, firstly we found the 3T3 cells, a mouse embryo fibroblast rodent cell line which does not express human DSG2, were able to be infected by HAdV-B55 after transfected with pcDNA3.1-DSG2, while normal 3T3 cells were still unsusceptible to HAdV-B55 infection. Next, A549 cells with hDSG2 knock-down by siRNA were hard to be infected by HAdV-B3/-B14/-B55, while the control siRNA group was still able to be infected by all these types of HAdVs. Finally, immunofluorescence confocal microscopy indicated visually that Cy3-conjugated HAdV-B55 viruses entered A549 cells by binding to DSG2 protein. Therefore, DSG2 is a major receptor of HAdV-B55 causing adult CAP. Our finding is important for better understanding of interactions between adenoviruses and host cells and may shed light on the development of new drugs that can interfere with these processes as well as for the development of potent prophylactic vaccines.

Systemic cancer therapy with engineered adenovirus that evades innate immunity

Oncolytic virus therapy is a cancer treatment modality that has the potential to improve outcomes for patients with currently incurable malignancies. Although intravascular delivery of therapeutic viruses provides access to disseminated tumors, this delivery route exposes the virus to opsonizing and inactivating factors in the blood, which limit the effective therapeutic virus dose and contribute to activation of systemic toxicities. When human species C adenovirus HAdv-C5 is delivered intravenously, natural immunoglobulin M (IgM) antibodies and coagulation factor X rapidly opsonize HAdv-C5, leading to virus sequestration in tissue macrophages and promoting infection of liver cells, triggering hepatotoxicity. Here, we showed that natural IgM antibody binds to the hypervariable region 1 (HVR1) of the main HAdv-C5 capsid protein hexon. Using compound targeted mutagenesis of hexon HVR1 loop and other functional sites that mediate virus-host interactions, we engineered and obtained a high-resolution cryo-electron microscopy structure of an adenovirus vector, Ad5-3M, which resisted inactivation by blood factors, avoided sequestration in liver macrophages, and failed to trigger hepatotoxicity after intravenous delivery. Systemic delivery of Ad5-3M to mice with localized or disseminated lung cancer led to viral replication in tumor cells, suppression of tumor growth, and prolonged survival. Thus, compound targeted mutagenesis of functional sites in the virus capsid represents a generalizable approach to tailor virus interactions with the humoral and cellular arms of the immune system, enabling generation of "designer" viruses with improved therapeutic properties.

ML-AdVInfect: A Machine-Learning Based Adenoviral Infection Predictor

Adenoviruses (AdVs) constitute a diverse family with many pathogenic types that infect a broad range of hosts. Understanding the pathogenesis of adenoviral infections is not only clinically relevant but also important to elucidate the potential use of AdVs as vectors in therapeutic applications. For an adenoviral infection to occur, attachment of the viral ligand to a cellular receptor on the host organism is a prerequisite and, in this sense, it is a criterion to decide whether an adenoviral infection can potentially happen. The interaction between any virus and its corresponding host organism is a specific kind of protein-protein interaction (PPI) and several experimental techniques, including high-throughput methods are being used in exploring such interactions. As a result, there has been accumulating data on virus-host interactions including a significant portion reported at publicly available bioinformatics resources. There is not, however, a computational model to integrate and interpret the existing data to draw out concise decisions, such as whether an infection happens or not. In this study, accepting the cellular entry of AdV as a decisive parameter for infectivity, we have developed a machine learning, more precisely support vector machine (SVM), based methodology to predict whether adenoviral infection can take place in a given host. For this purpose, we used the sequence data of the known receptors of AdVs, we identified sets of adenoviral ligands and their respective host species, and eventually, we have constructed a comprehensive adenovirus–host interaction dataset. Then, we committed interaction predictions through publicly available virus-host PPI tools and constructed an AdV infection predictor model using SVM with RBF kernel, with the overall sensitivity, specificity, and AUC of 0.88 ± 0.011, 0.83 ± 0.064, and 0.86 ± 0.030, respectively. ML-AdVInfect is the first of its kind as an effective predictor to screen the infection capacity along with anticipating any cross-species shifts. We anticipate our approach led to ML-AdVInfect can be adapted in making predictions for other viral infections.

Adenovirus - a blueprint for gene delivery

A central quest in gene therapy and vaccination is to achieve effective and long-lasting gene expression at minimal dosage. Adenovirus vectors are widely used therapeutics and safely deliver genes into many cell types. Adenoviruses evolved to use elaborate trafficking and particle deconstruction processes, and efficient gene expression and progeny formation. Here, we discuss recent insights into how human adenoviruses deliver their double-stranded DNA genome into cell nuclei, and effect lytic cell killing, non-lytic persistent infection or vector gene expression. The mechanisms underlying adenovirus entry, uncoating, nuclear transport and gene expression provide a blueprint for the emerging field of synthetic virology, where artificial virus-like particles are evolved to deliver therapeutic payload into human cells without viral proteins and genomes.

The endoplasmic reticulum unfolded protein response - homeostasis, cell death and evolution in virus infections

Viruses elicit cell and organismic stress, and offset homeostasis. They trigger intrinsic, innate and adaptive immune responses, which limit infection. Viruses restore homeostasis by harnessing evolutionary conserved stress responses, such as the endoplasmic reticulum (ER) unfolded protein response (UPR^ER). The canonical UPR^ER restores homeostasis based on a cell-autonomous signalling network modulating transcriptional and translational output. The UPR^ER remedies cell damage, but upon severe and chronic stress leads to cell death. Signals from the UPR^ER flow along three branches with distinct stress sensors, the inositol requiring enzyme (Ire) 1, protein kinase R (PKR)-like ER kinase (PERK), and the activating transcription factor 6 (ATF6). This review shows how both enveloped and non-enveloped viruses use the UPR^ER to control cell stress and metabolic pathways, and thereby enhance infection and progeny formation, or undergo cell death. We highlight how the Ire1 axis bypasses apoptosis, boosts viral transcription and maintains dormant viral genomes during latency and persistence periods concurrent with long term survival of infected cells. These considerations open new options for oncolytic virus therapies against cancer cells where the UPR^ER is frequently upregulated. We conclude with a discussion of the evolutionary impact that viruses, in particular retroviruses, and anti-viral defense has on the UPR^ER.

Single-cell RNA sequencing reveals SARS-CoV-2 infection dynamics in lungs of African green monkeys

Detailed knowledge about the dynamics of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection is important for uncovering the viral and host factors that contribute to coronavirus disease 2019 (COVID-19) pathogenesis. Old-World nonhuman primates recapitulate mild to moderate cases of COVID-19, thereby serving as important pathogenesis models. We compared African green monkeys inoculated with infectious SARS-CoV-2 or irradiated, inactivated virus to study the dynamics of virus replication throughout the respiratory tract. Genomic RNA from the animals inoculated with the irradiated virus was found to be highly stable, whereas subgenomic RNA, an indicator of viral replication, was found to degrade quickly. We combined this information with single-cell RNA sequencing of cells isolated from the lung and lung-draining mediastinal lymph nodes and developed new analysis methods for unbiased targeting of important cells in the host response to SARS-CoV-2 infection. Through detection of reads to the viral genome, we were able to determine that replication of the virus in the lungs appeared to occur mainly in pneumocytes, whereas macrophages drove the inflammatory response. Monocyte-derived macrophages recruited to the lungs, rather than tissue-resident alveolar macrophages, were most likely to be responsible for phagocytosis of infected cells and cellular debris early in infection, with their roles switching during clearance of infection. Together, our dataset provides a detailed view of the dynamics of virus replication and host responses over the course of mild COVID-19 and serves as a valuable resource to identify therapeutic targets.

Single-cell RNA sequencing reveals SARS-CoV-2 infection dynamics in lungs of African green monkeys

Detailed knowledge about the dynamics of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection is important for uncovering the viral and host factors that contribute to coronavirus disease 2019 (COVID-19) pathogenesis. Old-World nonhuman primates recapitulate mild to moderate cases of COVID-19, thereby serving as important pathogenesis models. We compared African green monkeys inoculated with infectious SARS-CoV-2 or irradiated, inactivated virus to study the dynamics of virus replication throughout the respiratory tract. Genomic RNA from the animals inoculated with the irradiated virus was found to be highly stable, whereas subgenomic RNA, an indicator of viral replication, was found to degrade quickly. We combined this information with single-cell RNA sequencing of cells isolated from the lung and lung-draining mediastinal lymph nodes and developed new analysis methods for unbiased targeting of important cells in the host response to SARS-CoV-2 infection. Through detection of reads to the viral genome, we were able to determine that replication of the virus in the lungs appeared to occur mainly in pneumocytes, whereas macrophages drove the inflammatory response. Monocyte-derived macrophages recruited to the lungs, rather than tissue-resident alveolar macrophages, were most likely to be responsible for phagocytosis of infected cells and cellular debris early in infection, with their roles switching during clearance of infection. Together, our dataset provides a detailed view of the dynamics of virus replication and host responses over the course of mild COVID-19 and serves as a valuable resource to identify therapeutic targets.

Differential responses of murine alveolar macrophages to elongate mineral particles of asbestiform and non-asbestiform varieties: Cytotoxicity, cytokine secretion and transcriptional changes

Human exposures to asbestiform elongate mineral particles (EMP) may lead to diffuse fibrosis, lung cancer, malignant mesothelioma and autoimmune diseases. Cleavage fragments (CF) are chemically identical to asbestiform varieties (or habits) of the parent mineral, but no consensus exists on whether to treat them as asbestos from toxicological and regulatory standpoints. Alveolar macrophages (AM) are the first responders to inhaled particulates, participating in clearance and activating other resident and recruited immunocompetent cells, impacting the long-term outcomes. In this study we address how EMP of asbestiform versus non-asbestiform habit affect AM responses. Max Planck Institute (MPI) cells, a non-transformed mouse line that has an AM phenotype and genotype, were treated with mass-, surface area- (s.a.), and particle number- (p.n.) equivalent concentrations of respirable asbestiform and non-asbestiform riebeckite/tremolite EMP for 24 h. Cytotoxicity, cytokines secretion and transcriptional changes were evaluated. At the equal mass, asbestiform EMP were more cytotoxic, however EMP of both habits induced similar LDH leakage and decrease in viability at s.a. and p.n. equivalent doses. DNA damage assessment and cell cycle analysis revealed differences in the modes of cell death between asbestos and respective CF. There was an increase in chemokines, but not pro-inflammatory cytokines after all EMP treatments. Principal component analysis of the cytokine secretion showed close clustering for the s.a. and p.n. equivalent treatments. There were mineral- and habit-specific patterns of gene expression dysregulation at s.a. equivalent doses. Our study reveals the critical nature of EMP morphometric parameters for exposure assessment and dosing approaches used in toxicity studies.

Species D Adenoviruses as Oncolytic Viral Vectors

Oncolytic adenoviruses (Ad) have shown promising results in the therapeutic treatment of cancer. Ad type 5 (Ad5) is the most extensively utilized Ad type. However, several limitations exist to using Ad5 as an oncolytic virus, including high levels of anti-Ad5 neutralizing antibodies in the population, binding of the Ad5 hexon to blood coagulation factor X leading to liver sequestration and toxicity, and reduced expression of the primary receptor CAR on many tumors. Here, we use in vitro methods to explore the oncolytic potential of four alternative Ad types (Ad26, 28, 45, and 48) belonging to the species D Ad subgroup and developed replication-competent species D Ads expressing the human sodium iodide symporter protein (hNIS) for combination radiovirotherapy. We evaluated the species D Ad vectors transduction, replication, cytotoxicity, and gene expression in six different cancer cell lines. Species D Ads showed the greatest transduction and cytotoxic killing in the SKBR3 breast cancer cells, followed by 293, A549, and HepG2 cells, however the cytotoxicity was less than the wild type Ad5 virus. In contrast, species D Ads showed limited transduction and cytotoxicity in the Hela and SKOV3 cancer cell lines. These species D Ad vectors also successfully expressed the hNIS gene during infection leading to increased iodide uptake in multiple cancer cell lines. These results, the low seroprevalence of anti-species D antibodies, and the lack of binding to blood coagulation FX, support further exploration of species D Ads as alternative oncolytic adenoviruses against multiple types of cancer.

Enhanced expression of coxsackievirus and adenovirus receptor in lipopolysaccharide-induced inflammatory macrophages is through TRIF-dependent innate immunity pathway

AIMS

Inflammatory macrophages have been proposed as a therapeutic target for joint disorders caused by inflammation. This study aimed to investigate the expression and regulation of coxsackievirus-adenovirus receptor (CAR) in lipopolysaccharide (LPS)-stimulated inflammatory macrophages whereby to evaluate the feasibility of virus-directed enzyme prodrug therapy (VDEPT).

MAIN METHODS

Macrophage cell lines (RAW264.7 and J774A.1) and primary macrophage cells derived from rat spleen were used to evaluate the expression of CAR protein or CAR mRNA. Specific inhibitors for TLR4 pathway were used to investigate the regulation of CAR expression. CAR expression in rat joints was documented by immunohistochemistry. Conditionally replicating adenovirus, CRAd-EGFP(PS1217L) or CRAd-NTR(PS1217H6), and non-replicating adenovirus CTL102 were used to transduce genes for enhanced green fluorescent protein (EGFP) or nitroreductase (NTR), respectively. The expression of EGFP, NTR, and the toxicity induced by CB1954 activation were evaluated.

KEY FINDINGS

The in vitro experiments revealed that CAR upregulation was mediated through the TLR4/TRIF/IRF3 pathway in LPS-stimulated inflammatory macrophage RAW264.7 and J774A.1 cells. The inflammatory RAW264.7 cells upregulated CAR expression following LPS stimulation, leading to higher infectability, increased NTR expression, and enhanced sensitization to CB1954. In animal experiments, the induction of CAR expression was observed in the CD68-expressing primary macrophages and in the CD68-expressing macrophages within joints following LPS stimulation.

SIGNIFICANCE

In conclusion, we report an enhanced CAR expression in inflammatory macrophages in vitro and in vivo through the immune response elicited by LPS. Thus, the TLR4/TRIF/IRF3 pathway of macrophages, when activated, could facilitate the therapeutic application of adenovirus-mediated VDEPT.

Cell-to-cell and genome-to-genome variability of adenovirus transcription tuned by the cell cycle

In clonal cultures, not all cells are equally susceptible to virus infection, and the mechanisms underlying this are poorly understood. Here, we developed image-based single-cell measurements to scrutinize the heterogeneity of adenovirus (AdV) infection. AdV delivers, transcribes and replicates a linear double-stranded DNA genome in the nucleus. We measured the abundance of viral transcripts using single-molecule RNA fluorescence in situ hybridization (FISH) and the incoming 5-ethynyl-2'-deoxycytidine (EdC)-tagged viral genomes using a copper(I)-catalyzed azide-alkyne cycloaddition (click) reaction. Surprisingly, expression of the immediate early gene E1A only moderately correlated with the number of viral genomes in the cell nucleus. Intranuclear genome-to-genome heterogeneity was found at the level of viral transcription and, in accordance, individual genomes exhibited heterogeneous replication activity. By analyzing the cell cycle state, we found that G1 cells exhibited the highest E1A gene expression and displayed increased correlation between E1A gene expression and viral genome copy numbers. The combined image-based single-molecule procedures described here are ideally suited to explore the cell-to-cell variability in viral gene expression in a range of different settings, including the innate immune response.

VLRs expression were significantly affected by complement C3 knockdown morphants in Lampetra morii

The complement component 3 of the lamprey, a jawless vertebrate, functions as an opsonin during the phagocytosis of rabbit red cells. Furthermore, lamprey C3 may be activated and cleaved into C3b, which is attached to the surface of target cells in the cytolytic process. However, the mechanism mediating the biological function of C3 in the lamprey is unknown. To our knowledge, this study is the first to show that variable lymphocyte receptors (VLRs) expression were significantly affected by complement C3 knockdown morphants in Lampetra morii. We identified the C3 gene in the lamprey genome based on its orthologs, conserved synteny, functional domains, phylogenetic tree, and conserved motifs. Additionally, we determined the optimal infection concentration of Aeromonas hydrophila to perform immune stimulation experiments in the lamprey larvae. The quantitative real-time polymerase chain reaction and immunofluorescence analyses revealed that the expression of Lampetra morii C3 (lmC3) was significantly upregulated in the larvae infected with 10⁷ CFU/mL of A. hydrophila. The lmC3 morphants (lmC3 MO) of lamprey larvae were generated by morpholino-mediated knockdown. The lmC3 MO larvae were highly susceptible to A. hydrophila infection, which indicated that lmC3 is critical in lamprey immune response. The expression of a selected panel of orthologous genes was comparatively analyzed in the infected wild type, infected lmC3 MO, infected control MO, uninfected wild type and uninfected lmC3 MO one-month-old ammocoete larvae. The knockdown of lmC3 strongly affected the expression of VLRA⁺/VLRB⁺/VLRC⁺-associated genes, which was also confirmed by immunohistochemical analysis. Thus, VLR expression were significantly affected by complement C3 knockdown morphants in Lampetra morii.

The E3 Ubiquitin Ligase Mind Bomb 1 Controls Adenovirus Genome Release at the Nuclear Pore Complex

Adenoviruses (AdVs) cause respiratory, ocular, and gastrointestinal tract infection and inflammation in immunocompetent people and life-threatening disease upon immunosuppression. AdV vectors are widely used in gene therapy and vaccination. Incoming particles attach to nuclear pore complexes (NPCs) of post-mitotic cells, then rupture and deliver viral DNA (vDNA) to the nucleus or misdeliver to the cytosol. Our genome-wide RNAi screen in AdV-infected cells identified the RING-type E3 ubiquitin ligase Mind bomb 1 (Mib1) as a proviral host factor for AdV infection. Mib1 is implicated in Notch-Delta signaling, ciliary biogenesis, and RNA innate immunity. Mib1 depletion arrested incoming AdVs at NPCs. Induced expression of full-length but not ligase-defective Mib1 in knockout cells triggered vDNA uncoating from NPC-tethered virions, nuclear import, misdelivery of vDNA, and vDNA expression. Mib1 is an essential host factor for AdV uncoating in human cells, and it provides a new concept for licensing virion DNA delivery through the NPC.

Adenovirus Receptor Expression in Cancer and Its Multifaceted Role in Oncolytic Adenovirus Therapy

Oncolytic adenovirus therapy is believed to be a promising way to treat cancer patients. To be able to target tumor cells with an oncolytic adenovirus, expression of the adenovirus receptor on the tumor cell is essential. Different adenovirus types bind to different receptors on the cell, of which the expression can vary between tumor types. Pre-existing neutralizing immunity to human adenovirus species C type 5 (HAdV-C5) has hampered its therapeutic efficacy in clinical trials, hence several adenoviral vectors from different species are currently being developed as a means to evade pre-existing immunity. Therefore, knowledge on the expression of appropriate adenovirus receptors on tumor cells is important. This could aid in determining which tumor types would benefit most from treatment with a certain oncolytic adenovirus type. This review provides an overview of the known receptors for human adenoviruses and how their expression on tumor cells might be differentially regulated compared to healthy tissue, before and after standardized anticancer treatments. Mechanisms behind the up- or downregulation of adenovirus receptor expression are discussed, which could be used to find new targets for combination therapy to enhance the efficacy of oncolytic adenovirus therapy. Additionally, the utility of the adenovirus receptors in oncolytic virotherapy is examined, including their role in viral spread, which might even surpass their function as primary entry receptors. Finally, future directions are offered regarding the selection of adenovirus types to be used in oncolytic adenovirus therapy in the fight against cancer.

Entry of Epidemic Keratoconjunctivitis-Associated Human Adenovirus Type 37 in Human Corneal Epithelial Cells

Purpose

Ocular infection by human adenovirus species D type 37 (HAdV-D37) causes epidemic keratoconjunctivitis, a severe, hyperacute condition. The corneal component of epidemic keratoconjunctivitis begins upon infection of corneal epithelium, and the mechanism of viral entry dictates subsequent proinflammatory gene expression. Therefore, it is important to understand the specific pathways of adenoviral entry in these cells.

Methods

Transmission electron microscopy of primary and tert-immortalized human corneal epithelial cells infected with HAdV-D37 was performed to identify the means of viral entry. Confocal microscopy was used to determine intracellular trafficking. The results of targeted small interfering RNA and specific chemical inhibitors were analyzed by quantitative PCR, and Western blot.

Results

By transmission electron microscopy, HAdV-D37 was seen to enter by both clathrin-coated pits and macropinocytosis; however, entry was both pH and dynamin 2 independent. Small interfering RNA against clathrin, AP2A1, and lysosome-associated membrane protein 1, but not early endosome antigen 1, decreased early viral gene expression. Ethyl-isopropyl amiloride, which blocks micropinocytosis, did not affect HAdV-D37 entry, but IPA, an inhibitor of p21-activated kinase, and important to actin polymerization, decreased viral entry in a dose-dependent manner.

Conclusions

HAdV-D37 enters human corneal epithelial cells by a noncanonical clathrin-mediated pathway involving lysosome-associated membrane protein 1 and PAK1, independent of pH, dynamin, and early endosome antigen 1. We showed earlier that HAdV-D37 enters human keratocytes through caveolae. Therefore, epidemic keratoconjunctivitis-associated viruses enter different corneal cell types via disparate pathways, which could account for a relative paucity of proinflammatory gene expression upon infection of corneal epithelial cells compared with keratocytes, as seen in prior studies.

Lactoferrin-Hexon Interactions Mediate CAR-Independent Adenovirus Infection of Human Respiratory Cells

Many viruses enter target cells using cell adhesion molecules as receptors. Paradoxically, these molecules are abundant on the lateral and basolateral side of intact, polarized, epithelial target cells, but absent on the apical side that must be penetrated by incoming viruses to initiate infection. Our study provides a model whereby viruses use different mechanisms to infect polarized epithelial cells depending on which side of the cell—apical or lateral/basolateral—is attacked. This study may also be useful to understand the biology of other viruses that use cell adhesion molecules as receptors.

Virus entry into host cells is a complex process that is largely regulated by access to specific cellular receptors. Human adenoviruses (HAdVs) and many other viruses use cell adhesion molecules such as the coxsackievirus and adenovirus receptor (CAR) for attachment to and entry into target cells. These molecules are rarely expressed on the apical side of polarized epithelial cells, which raises the question of how adenoviruses—and other viruses that engage cell adhesion molecules—enter polarized cells from the apical side to initiate infection. We have previously shown that species C HAdVs utilize lactoferrin—a common innate immune component secreted to respiratory mucosa—for infection via unknown mechanisms. Using a series of biochemical, cellular, and molecular biology approaches, we mapped this effect to the proteolytically cleavable, positively charged, N-terminal 49 residues of human lactoferrin (hLF) known as human lactoferricin (hLfcin). Lactoferricin (Lfcin) binds to the hexon protein on the viral capsid and anchors the virus to an unknown receptor structure of target cells, resulting in infection. These findings suggest that HAdVs use distinct cell entry mechanisms at different stages of infection. To initiate infection, entry is likely to occur at the apical side of polarized epithelial cells, largely by means of hLF and hLfcin bridging HAdV capsids via hexons to as-yet-unknown receptors; when infection is established, progeny virions released from the basolateral side enter neighboring cells by means of hLF/hLfcin and CAR in parallel.

IMPORTANCE Many viruses enter target cells using cell adhesion molecules as receptors. Paradoxically, these molecules are abundant on the lateral and basolateral side of intact, polarized, epithelial target cells, but absent on the apical side that must be penetrated by incoming viruses to initiate infection. Our study provides a model whereby viruses use different mechanisms to infect polarized epithelial cells depending on which side of the cell—apical or lateral/basolateral—is attacked. This study may also be useful to understand the biology of other viruses that use cell adhesion molecules as receptors.

Retargeting adenoviruses for therapeutic applications and vaccines

Adenoviruses (Ads) are robust vectors for therapeutic applications and vaccines, but their use can be limited by differences in their in vitro and in vivo pharmacologies. This review emphasizes that there is not just one Ad, but a whole virome of diverse viruses that can be used as therapeutics. It discusses that true vector targeting involves not only retargeting viruses, but importantly also detargeting the viruses from off-target cells.

Adenovirus 14p1 Immunopathogenesis during Lung Infection in the Syrian Hamster

Adenovirus (Ad) infections are usually mild and self-limited, with minimal inflammatory responses. During worldwide outbreaks, Ad14p1, an emerging Ad14 variant, has caused severe pulmonary disease, including acute respiratory distress syndrome (ARDS). This increased pathogenicity of Ad14p1 is not completely understood. In initial studies, we observed that infection of Syrian hamsters with Ad14p1 can cause a patchy bronchopneumonia, with an increased intensity of inflammation, compared to wild type Ad14 infection. The current study compared the dynamics of the immunopathogenesis of Ad14 and Ad14p1 infection of hamster lungs through the first two weeks after infection. Little difference was seen in infection-induced inflammation at day 1. Beginning at day 3, Ad14p1-infected hamsters showed marked inflammation that continued through to day 7. The inflammation began to resolve by day 10 but was still detectable at day 14. In contrast, Ad14-infected hamsters showed little inflammation during the 14-day period of observation. Inflammatory cell type analysis revealed that, at day 1, hamsters infected with either virus had predominantly neutrophil infiltration that began to resolve by day 3. However, at day 5, Ad14p1-infected hamsters had a second wave of neutrophil infiltration that was accompanied by edema which persisted to a variable extent through to day 10. These differences were not explained by an increased Ad14p1 replication rate, compared with Ad14 in vitro, but there was prolonged persistence of Ad14p1 in hamster lungs. There were differences in lung tissue cytokine and chemokine responses to Ad14p1 vs. Ad14 infection that might account for the increased leukocyte infiltrates in Ad14p1-infected hamsters. This animal model characterization provides the basis for future translational studies of the viral genetic mechanisms that control the increased immunopathogenesis of the emergent, Ad14p1 strain.

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.

Adenovirus flow in host cell networks

Viruses are obligatory parasites that take advantage of intracellular niches to replicate. During infection, their genomes are carried in capsids across the membranes of host cells to sites of virion production by exploiting cellular behaviour and resources to guide and achieve all aspects of delivery and the downstream virus manufacturing process. Successful entry hinges on execution of a precisely tuned viral uncoating program where incoming capsids disassemble in consecutive steps to ensure that genomes are released at the right time, and in the right place for replication to occur. Each step of disassembly is cell-assisted, involving individual pathways that transmit signals to regulate discrete functions, but at the same time, these signalling pathways are organized into larger networks, which communicate back and forth in complex ways in response to the presence of virus. In this review, we consider the elegant strategy by which adenoviruses (AdVs) target and navigate cellular networks to initiate the production of progeny virions. There are many remarkable aspects about the AdV entry program; for example, the virus gains targeted control of a large well-defined local network neighbourhood by coupling several interacting processes (including endocytosis, autophagy and microtubule trafficking) around a collective reference state centred on the interactional topology and multifunctional nature of protein VI. Understanding the network targeting activity of protein VI, as well as other built-in mechanisms that allow AdV particles to be efficient at navigating the subsystems of the cell, can be used to improve viral vectors, but also has potential to be incorporated for use in entirely novel delivery systems.

Acid ceramidase of macrophages traps herpes simplex virus in multivesicular bodies and protects from severe disease

Macrophages have important protective functions during infection with herpes simplex virus type 1 (HSV-1). However, molecular mechanisms that restrict viral propagation and protect from severe disease are unclear. Here we show that macrophages take up HSV-1 via endocytosis and transport the virions into multivesicular bodies (MVBs). In MVBs, acid ceramidase (aCDase) converts ceramide into sphingosine and increases the formation of sphingosine-rich intraluminal vesicles (ILVs). Once HSV-1 particles reach MVBs, sphingosine-rich ILVs bind to HSV-1 particles, which restricts fusion with the limiting endosomal membrane and prevents cellular infection. Lack of aCDase in macrophage cultures or in Asah1^-/- mice results in replication of HSV-1 and Asah1^-/- mice die soon after systemic or intravaginal inoculation. The treatment of macrophages with sphingosine enhancing compounds blocks HSV-1 propagation, suggesting a therapeutic potential of this pathway. In conclusion, aCDase loads ILVs with sphingosine, which prevents HSV-1 capsids from penetrating into the cytosol.

Expression profile of porcine scavenger receptor A and its role in bacterial phagocytosis by macrophages

Expression of scavenger receptor A (SRA) in macrophages plays key role in macrophage mediated uptake of microbes. However, little is known about the role of porcine scavenger receptor A (pSRA) in phagocytic function of macrophages in swine species. In this study, polyclonal antibody against pSRA was generated by using recombinant proteins to study expression and function of pSRA. We report broad expression of pSRA in different tissues. In the lungs, pSRA is mainly expressed by alveolar macrophages. Blockade of class A scavenger receptor by fucoidan treatment demonstrates that pSRA has role in bacterial phagocytosis by macrophages. Furthermore, importance of SRA-mediated bacterial phagocytosis has been shown using CHO cell line expressing pSRA. In summary, these findings reveal that pSRA, which is predominantly expressed in alveolar macrophages is likely to be an important receptor mediating recognition and uptake of bacteria in pig lungs.

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.

Time-resolved characterization of the mechanisms of toxicity induced by silica and amino-modified polystyrene on alveolar-like macrophages

Macrophages play a major role in the removal of foreign materials, including nano-sized materials, such as nanomedicines and other nanoparticles, which they accumulate very efficiently. Because of this, it is recognized that for a safe development of nanotechnologies and nanomedicine, it is essential to investigate potential effects induced by nano-sized materials on macrophages. To this aim, in this work, a recently established model of primary murine alveolar-like macrophages was used to investigate macrophage responses to two well-known nanoparticle models: 50 nm amino-modified polystyrene, known to induce cell death via lysosomal damage and apoptosis in different cell types, and 50 nm silica nanoparticles, which are generally considered non-toxic. Then, a time-resolved study was performed to characterize in detail the response of the macrophages following exposure to the two nanoparticles. As expected, exposure to the amino-modified polystyrene led to cell death, but surprisingly no lysosomal swelling or apoptosis were detected. On the contrary, a peculiar mitochondrial membrane hyperpolarization was observed, accompanied by endoplasmic reticulum stress (ER stress), increased cellular reactive oxygen species (ROS) and changes of metabolic activity, ultimately leading to cell death. Strong toxic responses were observed also after exposure to silica, which included mitochondrial ROS production, mitochondrial depolarization and cell death by apoptosis. Overall, these results showed that exposure to the two nanoparticles led to a very different series of intracellular events, suggesting that the macrophages responded differently to the two nanoparticle models. Similar time-resolved studies are required to characterize the response of macrophages to nanoparticles, as a key parameter in nanosafety assessment.

Antibody and DNA sensing pathways converge to activate the inflammasome during primary human macrophage infection

Inflammasomes are potent innate immune signalling complexes that couple cytokine release with pro-inflammatory cell death. However, pathogens have evolved strategies to evade this cell autonomous system. Here, we show how antibodies combine with innate sensors in primary human macrophages to detect viral infection and activate the inflammasome. Our data demonstrate that antibody opsonisation of virions can activate macrophages in multiple ways. In the first, antibody binding of adenovirus causes lysosomal damage, activating NLRP3 to drive inflammasome formation and IL-1β release. Importantly, this mechanism enhances virion capture but not infection and is accompanied by cell death, denying the opportunity for viral replication. Unexpectedly, we also find that antibody-coated viruses, which successfully escape into the cytosol, trigger a second system of inflammasome activation. These viruses are intercepted by the cytosolic antibody receptor TRIM21 and the DNA sensor cGAS. Together, these sensors stimulate both NLRP3 inflammasome formation and NFκB activation, driving dose-dependent IL-1β and TNF secretion, without inducing cell death. Our data highlight the importance of cooperativity between multiple sensing networks to expose viruses to the inflammasome pathway, which is particularly important for how our innate immune system responds to infection in the presence of pre-existing immunity.

Adenovirus Entry: From Infection to Immunity

More than 80 different adenovirus (AdV) types infect humans through the respiratory, ocular, or gastrointestinal tracts. They cause acute clinical mani-festations or persist under humoral and cell-based immunity. Immuno-suppressed individuals are at risk of death from an AdV infection. Concepts about cell entry of AdV build on strong foundations from molecular and cellular biology-and increasingly physical virology. Here, we discuss how virions enter and deliver their genome into the nucleus of epithelial cells. This process breaks open the virion at distinct sites because the particle has nonisometric mechanical strength and reacts to specific host factors along the entry pathway. We further describe how macrophages and dendritic cells resist AdV infection yet enhance productive entry into polarized epithelial cells. A deep understanding of the viral mechanisms and cell biological and biophysical principles will continue to unravel how epithelial and antigen-presenting cells respond to AdVs and control inflammation and persistence in pathology and therapy.

Therapeutic effects of scavenger receptor MARCO ligand on silica-induced pulmonary fibrosis in rats

Pulmonary fibrosis induced by prolonged exposure to silica particles is a chronic and irreversible lung disease without effective treatment till now. Our previous study has shown that early intervention with MARCO antagonist PolyG could alleviate pulmonary fibrosis in silica-exposed rats. However, the therapeutic effects of PolyG on silica-induced pulmonary fibrosis have rarely been reported. In this study, we explored the effects of administration (on the 28th day after silica exposure) of PolyG (MARCO inhibitor) on an established rat silicosis model. The lungs were analyzed histopathologically in rats using HE and Masson staining. The silica-induced ERS-related apoptosis, EMT and fibrosis were evaluated using western blotting, qRT-PCR and immunohistochemical analyses. The results suggested that silica exposure could increase the MARCO activity, and induce ERS and EMT in lung tissues. Pharmacological targeting of MARCO with PolyG attenuated the development of pulmonary fibrosis in silica-exposed rats. Further study indicated that PolyG could inhibit silica-induced ERS-related apoptosis and EMT process. Together, our findings reveal an essential function of ERS-related apoptosis and EMT in the processes of pulmonary fibrosis caused by silica, and identify MARCO as a potential therapeutic pharmacological target for silicosis.

Class A Scavenger Receptors Are Used by Frog Virus 3 During Its Cellular Entry

Frog virus 3 (FV3) is the type species of the genus Ranavirus (family Iridoviridae). FV3 and FV3-like viruses are globally distributed infectious agents with the capacity to replicate in three vertebrate classes (teleosts, amphibians, and reptiles). At the cellular level, FV3 and FV3-like viruses can infect cells from virtually all vertebrate classes. To date, the cellular receptors that are involved in the FV3 entry process are unknown. Class A scavenger receptors (SR-As) are a family of evolutionarily conserved cell-surface receptors that bind a wide range of chemically distinct polyanionic ligands and can function as cellular receptors for other DNA viruses, including vaccinia virus and herpes simplex virus. The present study aimed to determine whether SR-As are involved in FV3 cellular entry. By using well-defined SR-A competitive and non-competitive ligand-blocking assays and absolute qPCR, we demonstrated that the SR-A competitive ligands drastically reduced the quantities of cell-associated viral loads in frog cells. Moreover, inducing the expression of a human SR-AI in an SR-A null cell line significantly increased FV3⁻cell association. Together, our results indicate that SR-As are utilized by FV3 during the cellular entry process.

αvβ3 Integrin Is Required for Efficient Infection of Epithelial Cells with Human Adenovirus Type 26

Human adenoviruses (HAdVs) are being explored as vectors for gene transfer and vaccination. Human adenovirus type 26 (HAdV26), which belongs to the largest subgroup of adenoviruses, species D, has a short fiber and a so-far-unknown natural tropism. Due to its low seroprevalence, HAdV26 has been considered a promising vector for the development of vaccines. Despite the fact that the in vivo safety and immunogenicity of HAdV26 have been extensively studied, the basic biology of the virus with regard to receptor use, cell attachment, internalization, and intracellular trafficking is poorly understood. In this work, we investigated the roles of the coxsackievirus and adenovirus receptor (CAR), CD46, and αv integrins in HAdV26 infection of human epithelial cell lines. By performing different gain- and loss-of-function studies, we found that αvβ3 integrin is required for efficient infection of epithelial cells by HAdV26, while CAR and CD46 did not increase the transduction efficiency of HAdV26. By studying intracellular trafficking of fluorescently labeled HAdV26 in A549 cells and A549-derived cell clones with stably increased expression of αvβ3 integrin, we observed that HAdV26 colocalizes with αvβ3 integrin and that increased αvβ3 integrin enhances internalization of HAdV26. Thus, we conclude that HAdV26 uses αvβ3 integrin as a receptor for infecting epithelial cells. These results give us new insight into the HAdV26 infection pathway and will be helpful in further defining HAdV-based vector manufacturing and vaccination strategies.IMPORTANCE Adenovirus-based vectors are used today for gene transfer and vaccination. HAdV26 has emerged as a promising candidate vector for development of vaccines due to its relatively low seroprevalence and its ability to induce potent immune responses against inserted transgenes. However, data regarding the basic biology of the virus, like receptor usage or intracellular trafficking, are limited. In this work, we found that efficient infection of human epithelial cell lines by HAdV26 requires the expression of the αvβ3 integrin. By studying intracellular trafficking of fluorescently labeled HAdV26 in a cell clone with stably increased expression of αvβ3 integrin, we observed that HAdV26 colocalizes with αvβ3 integrin and confirmed that αvβ3 integrin expression facilitates efficient HAdV26 internalization. These results will allow further improvement of HAdV26-based vectors for gene transfer and vaccination.