Role of cellular heparan sulfate proteoglycans in infection of human adenovirus serotype 3 and 35

Construction and application of adenoviral vectors

Adenoviral vectors have been widely used as vaccine candidates or potential vaccine candidates against infectious diseases due to the convenience of genome manipulation, their ability to accommodate large exogenous gene fragments, easy access of obtaining high-titer of virus, and high efficiency of transduction. At the same time, adenoviral vectors have also been used extensively in clinical research for cancer gene therapy and treatment of diseases caused by a single gene defect. However, application of adenovirus also faces a series of challenges such as poor targeting, strong immune response against the vector itself, and they cannot be used repeatedly. It is believed that these problems will be solved gradually with further research and technological development in related fields. Here, we review the construction methods of adenoviral vectors, including "gutless" adenovirus and discuss application of adenoviral vectors as prophylactic vaccines for infectious pathogens and their application prospects as therapeutic vaccines for cancer and other kinds of chronic infectious disease such as human papillomavirus, hepatitis B virus, and hepatitis C virus.

Influence of Heparan Sulfate Proteoglycans and Factor X on species D Human Adenovirus Uptake and Transduction

More than 100 human adenovirus (Ad) types were identified, of which species D comprises the largest group. Heparan sulfate proteoglycans (HSPGs) were shown to function as cell surface receptors for cell binding and uptake of some Ads, but a systematic analysis of species D Ads is lacking. Previous research focused on Ad5 and blood coagulation factor X (FX) complexes, which revealed that Ad5 can transduce cells with low expression levels of its main coxsackievirus-adenovirus receptor in the presence of high HSPG expression levels in a FX dependent manner. Based on our reporter gene-tagged Ad-library, we explored for the first time a broad spectrum of species D Ads to study the role of HSPG on their cellular uptake. This study was performed on three Chinese Hamster Ovary (CHO) cell lines with different forms of HSPG (only proteoglycan (745), non-sulfated HSPG (606) or sulfated HSPG (K1)). The effect of Ad:FX complexes on Ad uptake was explored in the presence of physiological levels of FX in blood (6-10 µg/mL). We found that sulfation of HSPG plays an important role in cellular uptake and transduction of FX-bound Ad5 but neither HSPG nor FX influenced uptake of all tested species D Ads. Because FX has no influence on transduction efficiencies of species D Ads and therefore may not bind to them, these Ads may not be protected from attack by neutralizing IgM antibodies or the complement pathway, which may have implications for species D Ads used as vaccine and gene therapy vectors.

Role of Fiber Shaft Length in Tumor Targeting with Ad5/3 Vectors

Desmoglein 2 (DSG2) is overexpressed in many epithelial cancers and therefore represents a target receptor for oncolytic viruses, including Ad5/3-based viruses. For most Ad serotypes, the receptor-binding fiber is composed of tail, shaft, and knob domains. Here, we investigated the role of the fiber shaft in Ad5/3 tumor transduction in vitro and in human DSG2-transgenic mice carrying human DSG2high tumors. DSG2tg mice express DSG2 in a pattern similar to humans. We constructed Ad5/3L (with the "long" Ad5 shaft) and Ad5/3S (with the "short" Ad3 shaft) expressing GFP or luciferase. In in vitro studies we found that coagulation factor X, which is known to mediate undesired hepatocyte transduction of Ad5, enhances the transduction of Ad5/3(L), but not the transduction of Ad5/3(S). We therefore hypothesized that Ad5/3(S) would target DSG2high tumors while sparing the liver after intravenous injection. In vivo imaging studies for luciferase and analysis of luciferase activity in isolated organs, showed that Ad5/3(L) vectors efficiently transduced DSG2high tumors and liver but not normal epithelial tissues after intravenous injection. Ad5/3(S) showed minimal liver transduction, however it failed to transduce DSG2high tumors. Further modifications of the Ad5/3(S) capsid are required to compensate for the lower infectivity of Ad5/3(S) vectors.

Heparan Sulfate and Sialic Acid in Viral Attachment: Two Sides of the Same Coin?

Sialic acids and heparan sulfates make up the outermost part of the cell membrane and the extracellular matrix. Both structures are characterized by being negatively charged, serving as receptors for various pathogens, and are highly expressed in the respiratory and digestive tracts. Numerous viruses use heparan sulfates as receptors to infect cells; in this group are HSV, HPV, and SARS-CoV-2. Other viruses require the cell to express sialic acids, as is the case in influenza A viruses and adenoviruses. This review aims to present, in a general way, the participation of glycoconjugates in viral entry, and therapeutic strategies focused on inhibiting the interaction between the virus and the glycoconjugates. Interestingly, there are few studies that suggest the participation of both glycoconjugates in the viruses addressed here. Considering the biological redundancy that exists between heparan sulfates and sialic acids, we propose that it is important to jointly evaluate and design strategies that contemplate inhibiting the interactions of both glycoconjugates. This approach will allow identifying new receptors and lead to a deeper understanding of interspecies transmission.

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.

Coreceptor Functions of Cell Surface Heparan Sulfate Proteoglycans

Receptor-ligand interactions play an important role in many biological processes by triggering specific cellular responses. These interactions are frequently regulated by coreceptors that facilitate, alter, or inhibit signaling. Coreceptors work in parallel with other specific and accessory molecules to coordinate receptor-ligand interactions. Cell surface heparan sulfate proteoglycans (HSPGs) function as unique coreceptors because they can bind to many ligands and receptors through their HS and core protein motifs. Cell surface HSPGs are typically expressed in abundance of the signaling receptors and, thus, are capable of mediating the initial binding of ligands to the cell surface. HSPG coreceptors do not possess kinase domains or intrinsic enzyme activities and, for the most part, binding to cell surface HSPGs does not directly stimulate intracellular signaling. Because of these features, cell surface HSPGs primarily function as coreceptors for many receptor-ligand interactions. Given that cell surface HSPGs are widely conserved, they likely serve fundamental functions to preserve basic physiological processes. Indeed, cell surface HSPGs can support specific cellular interactions with growth factors, morphogens, chemokines, extracellular matrix (ECM) components, and microbial pathogens and their secreted virulence factors. Through these interactions, HSPG coreceptors regulate cell adhesion, proliferation, migration and differentiation, and impact the onset, progression, and outcome of pathophysiological processes, such as development, tissue repair, inflammation, infection, and tumorigenesis. This review seeks to provide an overview of the various mechanisms of how cell surface HSPGs function as coreceptors.

In Vitro and In Vivo Evaluation of Human Adenovirus Type 49 as a Vector for Therapeutic Applications

The human adenovirus phylogenetic tree is split across seven species (A-G). Species D adenoviruses offer potential advantages for gene therapy applications, with low rates of pre-existing immunity detected across screened populations. However, many aspects of the basic virology of species D-such as their cellular tropism, receptor usage, and in vivo biodistribution profile-remain unknown. Here, we have characterized human adenovirus type 49 (HAdV-D49)-a relatively understudied species D member. We report that HAdV-D49 does not appear to use a single pathway to gain cell entry, but appears able to interact with various surface molecules for entry. As such, HAdV-D49 can transduce a broad range of cell types in vitro, with variable engagement of blood coagulation FX. Interestingly, when comparing in vivo biodistribution to adenovirus type 5, HAdV-D49 vectors show reduced liver targeting, whilst maintaining transduction of lung and spleen. Overall, this presents HAdV-D49 as a robust viral vector platform for ex vivo manipulation of human cells, and for in vivo applications where the therapeutic goal is to target the lung or gain access to immune cells in the spleen, whilst avoiding liver interactions, such as intravascular vaccine applications.

Viruses Like Sugars: How to Assess Glycan Involvement in Viral Attachment

The first step of viral infection requires interaction with the host cell. Before finding the specific receptor that triggers entry, the majority of viruses interact with the glycocalyx. Identifying the carbohydrates that are specifically recognized by different viruses is important both for assessing the cellular tropism and for identifying new antiviral targets. Advances in the tools available for studying glycan-protein interactions have made it possible to identify them more rapidly; however, it is important to recognize the limitations of these methods in order to draw relevant conclusions. Here, we review different techniques: genetic screening, glycan arrays, enzymatic and pharmacological approaches, and surface plasmon resonance. We then detail the glycan interactions of enterovirus D68 and severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), highlighting the aspects that need further clarification.

Turkey adenovirus 3, a siadenovirus, uses sialic acid on N-linked glycoproteins as a cellular receptor

Turkey adenovirus 3 (TAdV-3) is the causative agent of an immune-mediated disease in turkeys, haemorrhagic enteritis, through targeting B lymphocytes. In the present study, we investigated the role of sialic acid in TAdV-3 entry and characterized the structural components of TAdV-3 receptor(s) on RP19, B lymphoblastoid cells. Removal of the cell-surface sialic acids by neuraminidases or blocking of sialic acids by wheat germ agglutinin lectin reduced virus infection. Pre-incubation of cells with Maackia amurensis lectin or Sambucus nigra agglutinin resulted in virus reduction, suggesting that TAdV-3 uses both α2,3-linked and α2,6-linked sialic acids as attachment receptor. Virus infectivity data from RP19 cells treated with sodium periodate, proteases (trypsin or bromelain) or metabolic inhibitors (dl-threo-1-phenyl-2-decanoylamino-3-morpholino-1-propanol, tunicamycin, or benzyl N-acetyl-α-d-galactosaminide) indicated that N-linked, but not O-linked, carbohydrates are part of the sialylated receptor and they are likely based on a membrane glycoprotein, rather than a glycolipid. Furthermore, our data, in conjunction with previous findings, implies that the secondary receptor for TAdV-3 is a protein molecule since the inhibition of glycolipid biosynthesis did not affect the virus infection, which was rather reduced by protease treatment. We can conclude that terminal sialic acids attached to N-linked membrane glycoproteins on B cells are used for virus attachment and are essential for successful virus infection.

Heparan Sulfate Is a Cellular Receptor for Enteric Human Adenoviruses

Human adenovirus (HAdV)-F40 and -F41 are leading causes of diarrhea and diarrhea-associated mortality in children under the age of five, but the mechanisms by which they infect host cells are poorly understood. HAdVs initiate infection through interactions between the knob domain of the fiber capsid protein and host cell receptors. Unlike most other HAdVs, HAdV-F40 and -F41 possess two different fiber proteins-a long fiber and a short fiber. Whereas the long fiber binds to the Coxsackievirus and adenovirus receptor (CAR), no binding partners have been identified for the short fiber. In this study, we identified heparan sulfate (HS) as an interaction partner for the short fiber of enteric HAdVs. We demonstrate that exposure to acidic pH, which mimics the environment of the stomach, inactivates the interaction of enteric adenovirus with CAR. However, the short fiber:HS interaction is resistant to and even enhanced by acidic pH, which allows attachment to host cells. Our results suggest a switch in receptor usage of enteric HAdVs after exposure to acidic pH and add to the understanding of the function of the short fibers. These results may also be useful for antiviral drug development and the utilization of enteric HAdVs for clinical applications such as vaccine development.

Advances in high-throughput methods for the identification of virus receptors

Viruses have evolved many mechanisms to invade host cells and establish successful infections. The interaction between viral attachment proteins and host cell receptors is the first and decisive step in establishing such infections, initiating virus entry into the host cells. Therefore, the identification of host receptors is fundamental in understanding pathogenesis and tissue tropism. Furthermore, receptor identification can inform the development of antivirals, vaccines, and diagnostic technologies, which have a substantial impact on human health. Nevertheless, due to the complex nature of virus entry, the redundancy in receptor usage, and the limitations in current identification methods, many host receptors remain elusive. Recent advances in targeted gene perturbation, high-throughput screening, and mass spectrometry have facilitated the discovery of virus receptors in recent years. In this review, we compare the current methods used within the field to identify virus receptors, focussing on genomic- and interactome-based approaches.

Antiviral effects of Cacicol®, a heparan sulfate biomimetic for corneal regeneration therapy, for herpes simplex virus type-1 and varicella zoster virus infection

BACKGROUND

Cacicol^®, a topical eye biopolymer containing a poly-carboxymethylglucose sulfate solution that is a regenerating matrix therapy agent, intended for wound healing of persistent corneal epithelial defects. Based on the chemical composition, we hypothesized that Cacicol^® may compete with natural heparan sulfate (HS) which initiates cell surface attachment of herpes simplex virus type-1 (HSV-1), varicella zoster virus (VZV) and human adenovirus (HAdV), three viruses associated with corneal infections.

METHODS

Cacicol^® was compared to vehicle in the following viral strains: HSV-1 SC16 strain and HSV-1 PSLR, a clinical isolate highly resistant to acyclovir and foscarnet; VZV ATH and VZV FLO, two VZV clinical isolates; and HAdV-D37 strain. Viruses in Cacicol^® or vehicle were added to cells for 1 h during adsorption then viral replication was assessed by plaque reduction assays on Vero cells for HSV-1 and MeWo cells for VZV and by immunostaining assay on Hep-2 cells for HAdV-D37.

RESULTS

The vehicle had no effect, dose-dependent effects were demonstrated when HSV-1 SC16, HSV-1 PSLR, VZV ATH and VZV FLO were inoculated in the presence of Cacicol^®, inhibiting viral replication by 98.4%, 98.9%, 90.1% and 89.0%, respectively. Cacicol^® had no antiviral effect against HAdV-D37.

CONCLUSIONS

Cacicol^® has a significant antiviral activity on HSV-1 and VZV, but not on HAdV-D37. The lack of effect on HAdV is probably because it is less dependent on HS interactions for cell entry. Clinical studies are necessary to determine Cacicol^® for an adjunct or alternative therapy of corneal HSV-1 or VZV infection, particularly for the management of antiviral resistant HSV-1.

Sulfated Glycosaminoglycans as Viral Decoy Receptors for Human Adenovirus Type 37

Glycans on plasma membranes and in secretions play important roles in infection by many viruses. Species D human adenovirus type 37 (HAdV-D37) is a major cause of epidemic keratoconjunctivitis (EKC) and infects target cells by interacting with sialic acid (SA)-containing glycans via the fiber knob domain of the viral fiber protein. HAdV-D37 also interacts with sulfated glycosaminoglycans (GAGs), but the outcome of this interaction remains unknown. Here, we investigated the molecular requirements of HAdV-D37 fiber knob:GAG interactions using a GAG microarray and demonstrated that fiber knob interacts with a broad range of sulfated GAGs. These interactions were corroborated in cell-based assays and by surface plasmon resonance analysis. Removal of heparan sulfate (HS) and sulfate groups from human corneal epithelial (HCE) cells by heparinase III and sodium chlorate treatments, respectively, reduced HAdV-D37 binding to cells. Remarkably, removal of HS by heparinase III enhanced the virus infection. Our results suggest that interaction of HAdV-D37 with sulfated GAGs in secretions and on plasma membranes prevents/delays the virus binding to SA-containing receptors and inhibits subsequent infection. We also found abundant HS in the basement membrane of the human corneal epithelium, which may act as a barrier to sub-epithelial infection. Collectively, our findings provide novel insights into the role of GAGs as viral decoy receptors and highlight the therapeutic potential of GAGs and/or GAG-mimetics in HAdV-D37 infection.

Non-Viral Delivery System and Targeted Bone Disease Therapy

Skeletal systems provide support, movement, and protection to the human body. It can be affected by several life suffering bone disorders such as osteoporosis, osteoarthritis, and bone cancers. It is not an easy job to treat bone disorders because of avascular cartilage regions. Treatment with non-specific drug delivery must utilize high doses of systemic administration, which may result in toxicities in non-skeletal tissues and low therapeutic efficacy. Therefore, in order to overcome such limitations, developments in targeted delivery systems are urgently needed. Although the idea of a general targeted delivery system using bone targeting moieties like bisphosphonates, tetracycline, and calcium phosphates emerged a few decades ago, identification of carrier systems like viral and non-viral vectors is a recent approach. Viral vectors have high transfection efficiency but are limited by inducing immunogenicity and oncogenicity. Although non-viral vectors possess low transfection efficiency they are comparatively safe. A number of non-viral vectors including cationic lipids, cationic polymers, and cationic peptides have been developed and used for targeted delivery of DNA, RNA, and drugs to bone tissues or cells with successful consequences. Here we mainly discuss such various non-viral delivery systems with respect to their mechanisms and applications in the specific targeting of bone tissues or cells. Moreover, we discuss possible therapeutic agents that can be delivered against various bone related disorders.

Intranasal Delivery of Adenoviral and AAV Vectors for Transduction of the Mammalian Peripheral Olfactory System

Intranasal delivery of solutions is a straightforward methodology for viral vector transduction and gene transfer to the epithelia within the nasal cavity. Beyond the simplicity of the technique, intranasal delivery has demonstrated restricted transduction of the olfactory and respiratory epithelial tissues. Here we outline the procedure of viral vector intranasal delivery in early postnatal and adult mice, as well as adult rats. The procedure allows for robust transduction and ectopic gene delivery that can be used for the visualization of cellular structures, protein distribution, and assessment of viral vector-mediated therapies.

Structure and N-acetylglucosamine binding of the distal domain of mouse adenovirus 2 fibre

Murine adenovirus 2 (MAdV-2) infects cells of the mouse gastrointestinal tract. Like human adenoviruses, it is a member of the genus Mastadenovirus, family Adenoviridae. The MAdV-2 genome has a single fibre gene that expresses a 787 residue-long protein. Through analogy to other adenovirus fibre proteins, it is expected that the carboxy-terminal virus-distal head domain of the fibre is responsible for binding to the host cell, although the natural receptor is unknown. The putative head domain has little sequence identity to adenovirus fibres of known structure. In this report, we present high-resolution crystal structures of the carboxy-terminal part of the MAdV-2 fibre. The structures reveal a domain with the typical adenovirus fibre head topology and a domain containing two triple β-spiral repeats of the shaft domain. Through glycan microarray profiling, saturation transfer difference nuclear magnetic resonance spectroscopy, isothermal titration calorimetry and site-directed mutagenesis, we show that the fibre specifically binds to the monosaccharide N-acetylglucosamine (GlcNAc). The crystal structure of the complex reveals that GlcNAc binds between the AB and CD loops at the top of each of the three monomers of the MAdV-2 fibre head. However, infection competition assays show that soluble GlcNAc monosaccharide and natural GlcNAc-containing polymers do not inhibit infection by MAdV-2. Furthermore, site-directed mutation of the GlcNAc-binding residues does not prevent the inhibition of infection by soluble fibre protein. On the other hand, we show that the MAdV-2 fibre protein binds GlcNAc-containing mucin glycans, which suggests that the MAdV-2 fibre protein may play a role in viral mucin penetration in the mouse gut.

Glycomics and Proteomics Approaches to Investigate Early Adenovirus-Host Cell Interactions

Adenoviruses as most viruses rely on glycan and protein interactions to attach to and enter susceptible host cells. The Adenoviridae family comprises more than 80 human types and they differ in their attachment factor and receptor usage, which likely contributes to the diverse tropism of the different types. In the past years, methods to systematically identify glycan and protein interactions have advanced. In particular sensitivity, speed and coverage of mass spectrometric analyses allow for high-throughput identification of glycans and peptides separated by liquid chromatography. Also, developments in glycan microarray technologies have led to targeted, high-throughput screening and identification of glycan-based receptors. The mapping of cell surface interactions of the diverse adenovirus types has implications for cell, tissue, and species tropism as well as drug development. Here we review known adenovirus interactions with glycan- and protein-based receptors, as well as glycomics and proteomics strategies to identify yet elusive virus receptors and attachment factors. We finally discuss challenges, bottlenecks, and future research directions in the field of non-enveloped virus entry into host cells.

Designer Oncolytic Adenovirus: Coming of Age

The licensing of talimogene laherparepvec (T-Vec) represented a landmark moment for oncolytic virotherapy, since it provided unequivocal evidence for the long-touted potential of genetically modified replicating viruses as anti-cancer agents. Whilst T-Vec is promising as a locally delivered virotherapy, especially in combination with immune-checkpoint inhibitors, the quest continues for a virus capable of specific tumour cell killing via systemic administration. One candidate is oncolytic adenovirus (Ad); it’s double stranded DNA genome is easily manipulated and a wide range of strategies and technologies have been employed to empower the vector with improved pharmacokinetics and tumour targeting ability. As well characterised clinical and experimental agents, we have detailed knowledge of adenoviruses’ mechanisms of pathogenicity, supported by detailed virological studies and in vivo interactions. In this review we highlight the strides made in the engineering of bespoke adenoviral vectors to specifically infect, replicate within, and destroy tumour cells. We discuss how mutations in genes regulating adenoviral replication after cell entry can be used to restrict replication to the tumour, and summarise how detailed knowledge of viral capsid interactions enable rational modification to eliminate native tropisms, and simultaneously promote active uptake by cancerous tissues. We argue that these designer-viruses, exploiting the viruses natural mechanisms and regulated at every level of replication, represent the ideal platforms for local overexpression of therapeutic transgenes such as immunomodulatory agents. Where T-Vec has paved the way, Ad-based vectors now follow. The era of designer oncolytic virotherapies looks decidedly as though it will soon become a reality.

Expression of human CD46 and trans-complementation by murine adenovirus 1 fails to allow productive infection by a group B oncolytic adenovirus in murine cancer cells

BACKGROUND

Oncolytic viruses are currently experiencing accelerated development in several laboratories worldwide, with some forty-seven clinical trials currently recruiting. Many oncolytic viruses combine targeted cytotoxicity to cancer cells with a proinflammatory cell lysis. Due to their additional potential to express immunomodulatory transgenes, they are also often known as oncolytic viral vaccines. However, several types of oncolytic viruses are human-specific and the lack of suitable immune-competent animal models complicates biologically relevant evaluation of their vaccine potential. This is a particular challenge for group B adenoviruses, which fail to infect even those immunocompetent animal model systems identified as semi-permissive for type 5 adenovirus. Here, we aim to develop a murine cell line capable of supporting replication of a group B oncolytic adenovirus, enadenotucirev (EnAd), for incorporation into a syngeneic immunocompetent animal model to explore the oncolytic vaccine potential of group B oncolytic viruses.

METHODS

Transgenic murine cell lines were infected with EnAd expressing GFP transgene under replication-independent or -dependent promoters. Virus mRNA expression, genome replication, and late protein expression were determined by qRT-PCR, qPCR, and immunoblotting, respectively. We also use Balb/c immune-competent mice to determine the tumourogenicity and infectivity of transgenic murine cell lines.

RESULTS

Our results show that a broad range of human carcinoma cells will support EnAd replication, but not murine carcinoma cells. Murine cells can be readily modified to express surface human CD46, one of the receptors for group B adenoviruses, allowing receptor-mediated uptake of EnAd particles into the murine cells and expression of CMV promoter-driven transgenes. Although the early E1A mRNA was expressed in murine cells at levels similar to human cells, adenovirus E2B and Fibre mRNA expression levels were hampered and few virus genomes were produced. Unlike previous reports on group C adenoviruses, trans-complementation of group B adenoviruses by co-infection with mouse adenovirus 1 did not rescue replication. A panel of group B adenoviruses expressing individual mouse adenovirus 1 genes were also unable to rescue EnAd replication.

CONCLUSION

Together, these results indicate that there may be major differences in the early stages of replication of group C and B adenoviruses in murine cells, and that the block to the life cycle of B adenoviruses in murine cells occurs in the early stage of virus replication, perhaps reflecting poor activity of Ad11p E1A in murine cells.

A general strategy for generating intact, full-length IgG antibodies that penetrate into the cytosol of living cells

Full-length IgG antibodies cannot cross cell membranes of living cells; this limits their use for direct targeting of cytosolic proteins. Here, we describe a general strategy for the generation of intact, full-length IgG antibodies, herein called cytotransmabs, which internalize into living cells and localize in the cytosol. We first generated a humanized light chain variable domain (VL) that could penetrate into the cytosol of living cells and was engineered for association with various subtypes of human heavy chain variable domains (VHs). When light chains with humanized VL were co-expressed with 3 heavy chains (HCs), including 2 HCs of the clinically approved adalimumab (Humira®) and bevacizumab (Avastin®), all 3 purified IgG antibodies were internalized into the cytoplasm of living cells. Cytotransmabs primarily internalized into living cells by the clathrin-mediated endocytic pathway through interactions with heparin sulfate proteoglycan that was expressed on the cell surface. The cytotransmabs escaped into the cytosol from early endosomes without being further transported into other cellular compartments, like the lysosomes, endoplasmic reticulum, Golgi apparatus, and nucleus. Furthermore, we generated a cytotransmab that co-localized with the targeted cytosolic protein when it was incubated with living cells, demonstrating that the cytotransmab can directly target cytosolic proteins. Internalized cytotransmabs did not show any noticeable cytotoxicity and remained in the cytosol for more than 6 h before being degraded by proteosomes. These results suggest that cytotransmabs, which efficiently enter living cells and reach the cytosolic space, will find widespread uses as research, diagnostic, and therapeutic agents.

Diversity of heparan sulfate and HSV entry: basic understanding and treatment strategies

A modified form of heparan sulfate (HS) known as 3-O-sulfated heparan sulfate (3-OS HS) generates fusion receptor for herpes simplex virus (HSV) entry and spread. Primary cultures of corneal fibroblasts derived from human eye donors have shown the clinical significance of this receptor during HSV corneal infection. 3-OS HS- is a product of a rare enzymatic modification at C3 position of glucosamine residue which is catalyzed by 3-O-sulfotransferases (3-OSTs) enzymes. From humans to zebrafish, the 3-OST enzymes are highly conserved and widely expressed in cells and tissues. There are multiple forms of 3-OSTs each producing unique subset of sulfated HS making it chemically diverse and heterogeneous. HSV infection of cells or zebrafish can be used as a unique tool to understand the structural-functional activities of HS and 3-OS HS and likewise, the infection can be used as a functional assay to screen phage display libraries for identifying HS and 3-OS HS binding peptides or small molecule inhibitors. Using this approach over 200 unique 12-mer HS and 3-OS HS recognizing peptides were isolated and characterized against HSV corneal infection where 3-OS HS is known to be a key receptor. In this review we discuss emerging role of 3-OS HS based therapeutic strategies in preventing viral infection and tissue damage.

Glycan Engagement by Viruses: Receptor Switches and Specificity

A large number of viruses, including many human pathogens, bind cell-surface glycans during the initial steps of infection. Viral glycan receptors such as glycosaminoglycans and sialic acid-containing carbohydrates are often negatively charged, but neutral glycans such as histo-blood group antigens can also function as receptors. The engagement of glycans facilitates attachment and entry and, consequently, is often a key determinant of the host range, tissue tropism, pathogenicity, and transmissibility of viruses. Here, we review current knowledge about virus-glycan interactions using representative crystal structures of viral attachment proteins in complex with glycans. We illuminate the determinants of specificity utilized by different glycan-binding viruses and explore the potential of these interactions for switching receptor specificities within or even between glycan classes. A detailed understanding of these parameters is important for the prediction of binding sites where structural information is not available, and is invaluable for the development of antiviral therapeutics.

Development of an AdEasy-based system to produce first- and second-generation adenoviral vectors with tropism for CAR- or CD46-positive cells

BACKGROUND

The AdEasy system has acquired preeminence amongst the various methods for producing first-generation, early region 1 (E1)-deleted human adenovirus (HAdV) vectors (AdVs) as a result of the fast and reproducible recovery of full-length AdV genomes via homologous recombination in Escherichia coli.

METHODS

From the classical AdEasy system, a new production platform was derived to assemble first- and second-generation [i.e. E1- plus early region 2A (E2A)-deleted] AdVs displaying on their surface HAdV serotype 5 (HAdV5) fibers (F5) or chimeric fibers (F5/50) comprising the tail of F5 and the fiber shaft and knob of HAdV serotype 50 (HAdV50). The CD46-interacting chimeric fibers allow for the high-level transduction of various human primary cell types of clinical interest with low or no surface expression of the Coxsackievirus and adenovirus receptor.

RESULTS

A new set of pAdEasy plasmid 'backbones' with or without E2A and encoding F5 or F5/50 was constructed and recombined in E. coli strain BJ5183 with a 'shuttle' plasmid coding for β-galactosidase. The resulting clones yielded AdV preparations with similar high titers following their rescue and propagation in producer cells. The AdVs with F5/50 were superior to those carrying F5 with respect to transducing human skeletal myocytes and mesenchymal stem cells.

CONCLUSIONS

In the present study, an AdEasy system tailored for the production of not only first-, but also second-generation AdVs equipped with the receptor-interacting fiber domains of the prototypic species C HAdV5 or of the species B member HAdV50 is presented. This system expands the range of applications for this robust and versatile AdV production platform.

Mutation of the fiber shaft heparan sulphate binding site of a 5/3 chimeric adenovirus reduces liver tropism

Natural tropism to the liver is a major obstacle in systemic delivery of adenoviruses in cancer gene therapy. Adenovirus binding to soluble coagulation factors and to cellular heparan sulphate proteoglycans via the fiber shaft KKTK domain are suggested to cause liver tropism. Serotype 5 adenovirus constructs with mutated KKTK regions exhibit liver detargeting, but they also transduce tumors less efficiently, possibly due to altered fiber conformation. We constructed Ad5/3lucS*, a 5/3 chimeric adenovirus with a mutated KKTK region. The fiber knob swap was hypothesized to facilitate tumor transduction. This construct was studied with or without additional coagulation factor ablation. Ad5/3lucS* exhibited significantly reduced transduction of human hepatic cells in vitro and mouse livers in vivo. Combination of coagulation factor ablation by warfarinization to Ad5/3lucS* seemed to further enhance liver detargeting. Cancer cell transduction by Ad5/3lucS* was retained in vitro. In vivo, viral particle accumulation in M4A4-LM3 xenograft tumors was comparable to controls, but Ad5/3lucS* transgene expression was nearly abolished. Coagulation factor ablation did not affect tumor transduction. These studies set the stage for further investigations into the effects of the KKTK mutation and coagulation factor ablation in the context of 5/3 serotype chimerism. Of note, the putative disconnect between tumor transduction and transgene expression could prove useful in further understanding of adenovirus biology.

Over-expression of human endosulfatase-1 exacerbates cadmium-induced injury to transformed human lung cells in vitro

Environmental exposure to cadmium is known to cause damage to alveolar epithelial cells of the lung, impair their capacity to repair, and result in permanent structural alterations. Cell surface heparan sulfate proteoglycans (HSPGs) can modulate cell responses to injury through their interactions with soluble effector molecules. These interactions are often sulfate specific, and the removal of sulfate groups from HS side chains could be expected to influence cellular injury, such as that caused by exposure to cadmium. The goal of this study was to define the role 6-O-sulfate plays in cellular responses to cadmium exposure in two pulmonary epithelial cancer cell lines (H292 and A549) and in normal human primary alveolar type II (hAT2) cells. Sulfate levels were modified by transduced transient over-expression of 6-O-endosulfatase (HSulf-1), a membrane-bound enzyme which specifically removes 6-O-sulfate groups from HSPG side chains. Results showed that cadmium decreased cell viability and activated apoptosis pathways at low concentrations in hAT2 cells but not in the cancer cells. HSulf-1 over-expression, on the contrary, decreased cell viability and activated apoptosis pathways in H292 and A549 cells but not in hAT2 cells. When combined with cadmium, HSulf-1 over-expression further decreased cell viability and exacerbated the activation of apoptosis pathways in the transformed cells but did not add to the toxicity in hAT2 cells. The finding that HSulf-1 sensitizes these cancer cells and intensifies the injury induced by cadmium suggests that 6-O-sulfate groups on HSPGs may play important roles in protection against certain environmental toxicants, such as heavy metals.

Adenovirus signalling in entry

Viruses carry nucleic acids between and within host cells. Invariably, virus attachment to host cells leads to activation of cell signalling. These so-called forward signals emerge from interactions with cell surface receptors or cytosolic proteins and elicit profound responses in the cells, for example induction of growth or innate immunity responses. They can enhance or suppress infection. In addition, viruses receive signals from the cell. These reverse signals can impact on the structure of the virus leading to genome uncoating. They can enhance infection or inactivate virus, for example by facilitating degradation. Here we discuss the nature and mechanisms by which forward and reverse signals emerge and affect the outcome of human adenovirus infections. We describe how human adenoviruses use cell surface receptors for forward signalling to activate cell growth, intracellular transport or innate immune response. We also discuss how adenoviruses use acto-myosin, integrins or microtubule-based kinesin motors for reverse signalling to facilitate their stepwise uncoating programme.

Symmetry-related clustering of positive charges is a common mechanism for heparan sulfate binding in enteroviruses

Coxsackievirus A9 (CAV9), a member of the Picornaviridae family, uses an RGD motif in the VP1 capsid protein to bind to integrin αvβ6 during cell entry. Here we report that two CAV9 isolates can bind to the heparan sulfate/heparin class of proteoglycans (HSPG). Sequence analysis identified an arginine (R) at position 132 in VP1 in these two isolates, rather than a threonine (T) as seen in the nonbinding strains tested. We introduced a T132R substitution into the HSPG-nonbinding strain Griggs and recovered infectious virus capable of binding to immobilized heparin, unlike the parental Griggs strain. The known CAV9 structure was used to identify the location of VP1 position 132, 5 copies of which were found to cluster around the 5-fold axis of symmetry, presumably producing a region of positive charge which can interact with the negatively charged HSPG. Analysis of several enteroviruses of the same species as CAV9, Human enterovirus B (HEV-B), identified examples from 5 types in which blocking of infection by heparin was coincident with an arginine (or another basic amino acid, lysine) at a position corresponding to 132 in VP1 in CAV9. Together, these data show that membrane-associated HSPG can serve as a (co)receptor for some CAV9 and other HEV-B strains and identify symmetry-related clustering of positive charges as one mechanism by which HSPG binding can be achieved. This is a potentially powerful mechanism by which a single amino acid change could generate novel receptor binding capabilities, underscoring the plasticity of host-cell interactions in enteroviruses.

Characterization of malleability and immunological properties of human adenovirus type 3 hexon hypervariable region 1

Adenovirus (Ad) capsids that display exogenous epitopes can be potently immunogenic, eliciting a potent humoral response against components of the capsid. We used the epitopes flag, his(6)flag, his(6)lgsflag and AdV4HVR5 as model antigens to characterize the hexon hypervariable region (HVR) 1 as a site for epitope insertion. A peptide of up to 17 amino acids could be incorporated into HVR1 of the Ad3 hexon without adversely affecting the biological characteristics of the virus. Multiple vaccinations with capsid-modified Ad3 induced a humoral response against the epitope inserted in HVR1. However, antiserum against the his(6)flag or his(6)lgsflag epitope did not recognize glutathione S-transferase (GST)-his(6) and GST-flag fusion protein. Our study illustrates that there is an immune response against the new epitope within the amino acids of his(6)flag or his(6)lgsflag epitopes. This discovery could be a warning for the generation of multivalent vaccine vectors by incorporation of multiple epitopes into single HVRs.

Chapter six--Adenovirus-based immunotherapy of cancer: promises to keep

Progress in vector design and an increased knowledge of mechanisms underlying tumor-induced immune suppression have led to a new and promising generation of Adenovirus (Ad)-based immunotherapies, which are discussed in this review. As vaccine vehicles Ad vectors (AdVs) have been clinically evaluated and proven safe, but a major limitation of the commonly used Ad5 serotype is neutralization by preexistent or rapidly induced immune responses. Genetic modifications in the Ad capsid can reduce intrinsic immunogenicity and facilitate escape from antibody-mediated neutralization. Further modification of the Ad hexon and fiber allows for liver and scavenger detargeting and selective targeting of, for example, dendritic cells. These next-generation Ad vaccines with enhanced efficacy are now becoming available for testing as tumor vaccines. In addition, AdVs encoding immune-modulating products may be used to convert the tumor microenvironment from immune-suppressive and proinvasive to proinflammatory, thus facilitating cell-mediated effector functions that can keep tumor growth and invasion in check. Oncolytic AdVs, that selectively replicate in tumor cells and induce an immunogenic form of cell death, can also be armed with immune-activating transgenes to amplify primed antitumor immune responses. These novel immunotherapy strategies, employing highly efficacious AdVs in optimized configurations, show great promise and warrant clinical exploration.

Adenovirus gene transfer to amelogenesis imperfecta ameloblast-like cells

To explore gene therapy strategies for amelogenesis imperfecta (AI), a human ameloblast-like cell population was established from third molars of an AI-affected patient. These cells were characterized by expression of cytokeratin 14, major enamel proteins and alkaline phosphatase staining. Suboptimal transduction of the ameloblast-like cells by an adenovirus type 5 (Ad5) vector was consistent with lower levels of the coxsackie-and-adenovirus receptor (CAR) on those cells relative to CAR-positive A549 cells. To overcome CAR -deficiency, we evaluated capsid-modified Ad5 vectors with various genetic capsid modifications including “pK7” and/or “RGD” motif-containing short peptides incorporated in the capsid protein fiber as well as fiber chimera with the Ad serotype 3 (Ad3) fiber “knob” domain. All fiber modifications provided an augmented transduction of AI-ameloblasts, revealed following vector dose normalization in A549 cells with a superior effect (up to 404-fold) of pK7/RGD double modification. This robust infectivity enhancement occurred through vector binding to both α_vβ3/α_vβ5 integrins and heparan sulfate proteoglycans (HSPGs) highly expressed by AI-ameloblasts as revealed by gene transfer blocking experiments. This work thus not only pioneers establishment of human AI ameloblast-like cell population as a model for in vitro studies but also reveals an optimal infectivity-enhancement strategy for a potential Ad5 vector-mediated gene therapy for AI.

Glycan microarrays for decoding the glycome

In the last decade, glycan microarrays have revolutionized the analysis of the specificity of glycan-binding proteins (GBPs), providing information that simultaneously illuminates the biology mediated by them and decodes the informational content of the glycome. Numerous methods have emerged for arraying glycans in a "chip" format, and glycan libraries have been assembled that address the diversity of the human glycome. Such arrays have been successfully used for analysis of GBPs, which mediate mammalian biology, host-pathogen interactions, and immune recognition of glycans relevant to vaccine production and cancer antigens. This review covers the development of glycan microarrays and applications that have provided insights into the roles of mammalian and microbial GBPs.

An adenovirus traffic update: from receptor engagement to the nuclear pore

Adenoviruses have a bipolar nature: they are ubiquitous pathogens that occasionally cause life-threatening diseases or they can be engineered into powerful gene transfer vectors. The goal of this article is to summarize the most recent advances in adenovirus receptor engagement, internalization, endosomal maturation, endosomal escape and trafficking to the nuclear pore. A better understanding of this initial part of the adenovirus lifecycle may identify new mechanistic-based treatments for adenovirus-induced diseases and help in the engineering of more efficient vectors.

Cell entry and trafficking of human adenovirus bound to blood factor X is determined by the fiber serotype and not hexon:heparan sulfate interaction

Human adenovirus serotype 5 (HAdV5)-based vectors administered intravenously accumulate in the liver as the result of their direct binding to blood coagulation factor X (FX) and subsequent interaction of the FX-HAdV5 complex with heparan sulfate proteoglycan (HSPG) at the surface of liver cells. Intriguingly, the serotype 35 fiber-pseudotyped vector HAdV5F35 has liver transduction efficiencies 4-logs lower than HAdV5, even though both vectors carry the same hexon capsomeres. In order to reconcile this apparent paradox, we investigated the possible role of other viral capsid proteins on the FX/HSPG-mediated cellular uptake of HAdV5-based vectors. Using CAR- and CD46-negative CHO cells varying in HSPG expression, we confirmed that FX bound to serotype 5 hexon protein and to HAdV5 and HAdV5F35 virions via its Gla-domain, and enhanced the binding of both vectors to surface-immobilized hypersulfated heparin and cellular HSPG. Using penton mutants, we found that the positive effect of FX on HAdV5 binding to HSPG and cell transduction did not depend on the penton base RGD and fiber shaft KKTK motifs. However, we found that FX had no enhancing effect on the HAdV5F35-mediated cell transduction, but a negative effect which did not involve the cell attachment or endocytic step, but the intracellular trafficking and nuclear import of the FX-HAdV5F35 complex. By cellular imaging, HAdV5F35 particles were observed to accumulate in the late endosomal compartment, and were released in significant amounts into the extracellular medium via exocytosis. We showed that the stability of serotype 5 hexon:FX interaction was higher at low pH compared to neutral pH, which could account for the retention of FX-HAdV5F35 complexes in the late endosomes. Our results suggested that, despite the high affinity interaction of hexon capsomeres to FX and cell surface HSPG, the adenoviral fiber acted as the dominant determinant of the internalization and trafficking pathway of HAdV5-based vectors.

Identification of amino acid residues important for heparan sulfate proteoglycan interaction within variable region 3 of the feline immunodeficiency virus surface glycoprotein

Heparan sulfate proteoglycans (HSPGs) act as binding receptors or attachment factors for the viral envelope of many viruses, including strains of HIV and feline immunodeficiency virus (FIV). The FIV gp95 glycoprotein (SU) from laboratory-adapted strains (tissue culture adapted [TCA]) such as FIV-34TF10 can bind to HSPG, whereas SU from field strains (FS) such as FIV-PPR cannot. Previous studies indicate that SU-HSPG interactions occur within the V3 loop. We utilized a series of nested V3 peptides to further map the HSPG binding sites and found that both sides of the predicted V3 loop stem were critical for the binding but not the CXCR4 binding domain near the predicted tip of the V3 loop. Neutralization assays for TCA strain entry using the same set of V3 peptides showed that peptides targeting CXCR4 or HSPG binding sites can block infection, supporting the V3 loop as a critical neutralization target. Site-directed mutagenesis identified two highly conserved arginines, R379 and R389, on the N-terminal side of the V3 stem as critical for the contact between SU and HSPG. Residues K407, K409, K410, and K412 on the C-terminal side of the V3 stem form a second nonconserved domain necessary for HSPG binding, consistent with the observed specificity distinctions with FS FIV. Our findings discriminate structural determinants important for HSPG and CXCR4 binding by FIV SU and thus further define the importance of the V3 loop for virus entry and infection.

Multimerization of adenovirus serotype 3 fiber knob domains is required for efficient binding of virus to desmoglein 2 and subsequent opening of epithelial junctions

Recently, we identified desmoglein 2 (DSG2) as the main receptor for a group of species B adenoviruses (Ads), including Ad3, a serotype that is widely distributed in the human population (H. Wang et al., Nat. Med. 17:96-104, 2011). In this study, we have attempted to delineate structural details of the Ad3 interaction with DSG2. For CAR- and CD46-interacting Ad serotypes, attachment to cells can be completely blocked by an excess of recombinant fiber knob protein, while soluble Ad3 fiber knob only inefficiently blocks Ad3 infection. We found that the DSG2-interacting domain(s) within Ad3 is formed by several fiber knob domains that have to be in the spatial constellation that is present in viral particles. Based on this finding, we generated a small recombinant, self-dimerizing protein containing the Ad3 fiber knob (Ad3-K/S/Kn). Ad3-K/S/Kn bound to DSG2 with high affinity and blocked Ad3 infection. We demonstrated by confocal immunofluorescence and transmission electron microscopy analyses that Ad3-K/S/Kn, through its binding to DSG2, triggered the transient opening of intercellular junctions in epithelial cells. The pretreatment of epithelial cells with Ad3-K/S/Kn resulted in increased access to receptors that are localized in or masked by epithelial junctions, e.g., CAR or Her2/neu. Ad3-K/S/Kn treatment released CAR from tight junctions and thus increased the transduction of epithelial cells by a serotype Ad5-based vector. Furthermore, the pretreatment of Her2/neu-positive breast cancer cells with Ad3-K/S/Kn increased the killing of cancer cells by the Her2/neu-targeting monoclonal antibody trastuzumab (Herceptin). This study widens our understanding of how Ads achieve high avidity to their receptors and the infection of epithelial tissue. The small recombinant protein Ad3-K/S/Kn has practical implications for the therapy of epithelial cancer and gene/drug delivery to normal epithelial tissues.

Lysosomal localization and mechanism of membrane penetration influence nonenveloped virus activation of the NLRP3 inflammasome

Adenovirus (Ad) endosomal membrane penetration activates the NLRP3 inflammasome by releasing lysosomal cathepsin B (catB) into the cytoplasm. We therefore examined the extent to which inflammasome activation correlates with Ad colocalization with catB-enriched lysosomes. Inflammasome activation, is greater during infections with Ad5 possessing an Ad16 fiber (Ad5F16gfp), or Ad5gfp neutralized by human serum, than Ad5gfp alone. Enhanced IL-1β release by Ad5F16gfp is partially due to increased TLR9 signaling but also correlates with greater release of catB into the cytoplasm. This increased TLR9 signaling and catB release correlates with a greater localization of Ad5F16gfp to lysosomes prior to endosomal escape. Another nonenveloped virus, reovirus, requires catB to penetrate cell membranes. However, reovirus did not release catB into the cytoplasm despite significantly greater colocalization with lysosomes compared to Ad5gfp and efficient membrane penetration. Thus, not only lysosomal localization, but the mechanism of membrane penetration influences viral activation of the NLRP3 inflammasome.

Heparan Sulfate Proteoglycans in Infection

To cause infections, microbial pathogens elaborate a multitude of factors that interact with host components. Using these host–pathogen interactions to their advantage, pathogens attach, invade, disseminate, and evade host defense mechanisms to promote their survival in the hostile host environment. Many viruses, bacteria, and parasites express adhesins that bind to cell surface heparan sulfate proteoglycans (HSPGs) to facilitate their initial attachment and subsequent cellular entry. Some pathogens also secrete virulence factors that modify HSPG expression. HSPGs are ubiquitously expressed on the cell surface of adherent cells and in the extracellular matrix. HSPGs are composed of one or several heparan sulfate (HS) glycosaminoglycan chains attached covalently to specific core proteins. For most intracellular pathogens, cell surface HSPGs serve as a scaffold that facilitates the interaction of microbes with secondary receptors that mediate host cell entry. Consistent with this mechanism, addition of HS or its pharmaceutical functional mimic, heparin, inhibits microbial attachment and entry into cultured host cells, and HS-binding pathogens can no longer attach or enter cultured host cells whose HS expression has been reduced by enzymatic treatment or chemical mutagenesis. In pathogens where the specific HS adhesin has been identified, mutant strains lacking HS adhesins are viable and show normal growth rates, suggesting that the capacity to interact with HSPGs is strictly a virulence activity. The goal of this chapter is to provide a mechanistic overview of our current understanding of how certain microbial pathogens subvert HSPGs to promote their infection, using specific HSPG–pathogen interactions as representative examples.

Oncolytic adenovirus based on serotype 3

Oncolytic adenoviruses have been safe in clinical trials but the efficacy has been mostly limited. All published trials have been performed with serotype 5 based viruses. The expression level of the Ad5 receptor CAR may be variable in advanced tumors. In contrast, the Ad3 receptor remains unclear, but is known to be abundantly expressed in most tumors. Therefore, we hypothesized that a fully serotype 3 oncolytic adenovirus might be useful for treating cancer. Patients exposed to adenoviruses develop high titers of serotype-specific neutralizing antibodies, which might compromise re-administration. Thus, having different serotype oncolytic viruses available might facilitate repeated dosing in humans. Ad3-hTERT-E1A is a fully serotype 3 oncolytic adenovirus controlled by the promoter of the catalytic domain of human telomerase. It was effective in vitro on cell lines representing seven major cancer types, although low toxicity was seen in non-malignant cells. In vivo, the virus had anti-tumor efficacy in three different animal models. Although in vitro oncolysis mediated by Ad3-hTERT-E1A and wild-type Ad3 occurred more slowly than with Ad5 or Ad5/3 (Ad3 fiber knob in Ad5) based viruses, in vivo the virus was at least as potent as controls. Anti-tumor efficacy was retained in presence of neutralizing anti-Ad5 antibodies whereas Ad5 based controls were blocked. In summary, we report generation of a non-Ad5 based oncolytic adenovirus, which might be useful for testing in cancer patients, especially in the context of high anti-Ad5 neutralizing antibodies.

Desmoglein 2 is a receptor for adenovirus serotypes 3, 7, 11 and 14

We have identified desmoglein 2 (DSG2) as the primary high-affinity receptor used by adenovirus (Ad) serotypes Ad3, Ad7, Ad11, and Ad14. These serotypes represent important human pathogens causing respiratory tract infections. In epithelial cells, adenovirus binding to DSG2 triggers events reminiscent of epithelial-to-mesenchymal transition, leading to transient opening of intercellular junctions. This improves access to receptors, e.g. CD46 and Her2/neu, that are trapped in intercellular junctions. In addition to complete virions, dodecahedral particles (PtDd), formed by viral penton and fiber in excess during viral replication, can trigger DSG2-mediated opening of intercellular junctions as shown by studies with recombinant Ad3 PtDd. Our findings shed light on adenovirus biology and pathogenesis and have implications for cancer therapy.

Tropism-modification strategies for targeted gene delivery using adenoviral vectors

Achieving high efficiency, targeted gene delivery with adenoviral vectors is a long-standing goal in the field of clinical gene therapy. To achieve this, platform vectors must combine efficient retargeting strategies with detargeting modifications to ablate native receptor binding (i.e. CAR/integrins/heparan sulfate proteoglycans) and “bridging” interactions. “Bridging” interactions refer to coagulation factor binding, namely coagulation factor X (FX), which bridges hepatocyte transduction in vivo through engagement with surface expressed heparan sulfate proteoglycans (HSPGs). These interactions can contribute to the off-target sequestration of Ad5 in the liver and its characteristic dose-limiting hepatotoxicity, thereby significantly limiting the in vivo targeting efficiency and clinical potential of Ad5-based therapeutics. To date, various approaches to retargeting adenoviruses (Ad) have been described. These include genetic modification strategies to incorporate peptide ligands (within fiber knob domain, fiber shaft, penton base, pIX or hexon), pseudotyping of capsid proteins to include whole fiber substitutions or fiber knob chimeras, pseudotyping with non-human Ad species or with capsid proteins derived from other viral families, hexon hypervariable region (HVR) substitutions and adapter-based conjugation/crosslinking of scFv, growth factors or monoclonal antibodies directed against surface-expressed target antigens. In order to maximize retargeting, strategies which permit detargeting from undesirable interactions between the Ad capsid and components of the circulatory system (e.g. coagulation factors, erythrocytes, pre-existing neutralizing antibodies), can be employed simultaneously. Detargeting can be achieved by genetic ablation of native receptor-binding determinants, ablation of “bridging interactions” such as those which occur between the hexon of Ad5 and coagulation factor X (FX), or alternatively, through the use of polymer-coated “stealth” vectors which avoid these interactions. Simultaneous retargeting and detargeting can be achieved by combining multiple genetic and/or chemical modifications.

Requirements for receptor engagement during infection by adenovirus complexed with blood coagulation factor X

Human adenoviruses from multiple species bind to coagulation factor X (FX), yet the importance of this interaction in adenovirus dissemination is unknown. Upon contact with blood, vectors based on adenovirus serotype 5 (Ad5) binds to FX via the hexon protein with nanomolar affinity, leading to selective uptake of the complex into the liver and spleen. The Ad5:FX complex putatively targets heparan sulfate proteoglycans (HSPGs). The aim of this study was to elucidate the specific requirements for Ad5:FX-mediated cellular uptake in this high-affinity pathway, specifically the HSPG receptor requirements as well as the role of penton base-mediated integrin engagement in subsequent internalisation. Removal of HS sidechains by enzymatic digestion or competition with highly-sulfated heparins/heparan sulfates significantly decreased FX-mediated Ad5 cell binding in vitro and ex vivo. Removal of N-linked and, in particular, O-linked sulfate groups significantly attenuated the inhibitory capabilities of heparin, while the chemical inhibition of endogenous HSPG sulfation dose-dependently reduced FX-mediated Ad5 cellular uptake. Unlike native heparin, modified heparins lacking O- or N-linked sulfate groups were unable to inhibit Ad5 accumulation in the liver 1h after intravascular administration of adenovirus. Similar results were observed in vitro using Ad5 vectors possessing mutations ablating CAR- and/or α(v) integrin binding, demonstrating that attachment of the Ad5:FX complex to the cell surface involves HSPG sulfation. Interestingly, Ad5 vectors ablated for α(v) integrin binding showed markedly delayed cell entry, highlighting the need for an efficient post-attachment internalisation signal for optimal Ad5 uptake and transport following surface binding mediated through FX. This study therefore integrates the established model of α(v) integrin-dependent adenoviral infection with the high-affinity FX-mediated pathway. This has important implications for mechanisms that define organ targeting following contact of human adenoviruses with blood.

N-terminal α-helix-independent membrane interactions facilitate adenovirus protein VI induction of membrane tubule formation

Adenovirus disrupts endosomal membranes during cell entry. The membrane lytic capsid protein VI (pVI) facilitates entry by fragmenting membranes. Although an N-terminal amphipathic α-helix (VI-Φ) possesses similar membrane affinity as pVI, truncated protein lacking VI-Φ (VIΔ54) still possesses moderate membrane affinity. We demonstrate that incorporation of nickel-NTA lipids in membranes enhances the membrane affinity and the membrane lytic activity of VIΔ54. We also demonstrate that 3 predicted pVI α-helices within residues 54-114 associate with membranes, sitting roughly parallel to the membrane surface. His-tagged VIΔ54 is capable of fragmenting membranes similar to pVI and the VI-Φ peptide. Interestingly, neither VI-Φ nor His-tagged VIΔ54 can induce tubule formation in giant lipid vesicles as observed for pVI. These data suggest cooperativity between the amphipathic α-helix and residues in VIΔ54 to induce positive membrane curvature and tubule formation. These results provide additional details regarding the mechanism of nonenveloped virus membrane penetration.

Adenovirus 5-fiber 35 chimeric vector mediates efficient apical correction of the cystic fibrosis transmembrane conductance regulator defect in cystic fibrosis primary airway epithelia

In vivo gene transfer to the human respiratory tract by adenovirus serotype 5 (Ad5) vectors has revealed their limitations related to inefficient gene transfer, host antiviral response, and innate adenoviral toxicity. In the present work, we compared the cytotoxicity and efficiency of Ad5 and a chimeric Ad5F35 vector with respect to CFTR gene transfer to cystic fibrosis (CF) and non-CF human airway epithelial cells. We found that high doses of Ad5 vector had an adverse effect on the function of exogenous and endogenous CFTR. Results obtained with Ad5 capsid mutants suggested that the RGD motifs on the penton base capsomers were responsible for the negative effect on CFTR function. This negative interference did not result from a lower level of biosynthesis and/or altered cellular trafficking of the CFTR protein, but rather from an indirect mechanism of functional blockage of CFTR, related to the RGD integrin-mediated endocytic pathway of Ad5. No negative interference with CFTR was observed for Ad5F35, an Ad5-based vector pseudotyped with fibers from Ad35, a serotype that uses another cell entry pathway. In vitro, Ad5F35 vector expressing the GFP-tagged CFTR (Ad5F35-GFP-CFTR) showed a 30-fold higher efficiency of transduction and chloride channel correction in CFTR-deficient cells, compared with Ad5GFP-CFTR. Ex vivo, Ad5F35-GFP-CFTR had the capacity to transduce efficiently reconstituted airway epithelia from patients with CF (CF-HAE) via the apical surface, restored chloride channel function at relatively low vector doses, and showed relatively stable expression of GFP-CFTR for several weeks.

Macropinocytotic uptake and infection of human epithelial cells with species B2 adenovirus type 35

Human adenovirus serotype 35 (HAdV-35; here referred to as Ad35) causes kidney and urinary tract infections and infects respiratory organs of immunocompromised individuals. Unlike other adenoviruses, Ad35 has a low seroprevalence, which makes Ad35-based vectors promising candidates for gene therapy. Ad35 utilizes CD46 and integrins as receptors for infection of epithelial and hematopoietic cells. Here we show that infectious entry of Ad35 into HeLa cells, human kidney HK-2 cells, and normal human lung fibroblasts strongly depended on CD46 and integrins but not heparan sulfate and variably required the large GTPase dynamin. Ad35 infections were independent of expression of the carboxy-terminal domain of AP180, which effectively blocks clathrin-mediated uptake. Ad35 infections were inhibited by small chemicals against serine/threonine kinase Pak1 (p21-activated kinase), protein kinase C (PKC), sodium-proton exchangers, actin, and acidic organelles. Remarkably, the F-actin inhibitor jasplakinolide, the Pak1 inhibitor IPA-3, or the sodium-proton exchange inhibitor 5-(N-ethyl-N-isopropyl) amiloride (EIPA) blocked endocytic uptake of Ad35. Dominant-negative proteins or small interfering RNAs against factors driving macropinocytosis, including the small GTPase Rac1, Pak1, or the Pak1 effector C-terminal binding protein 1 (CtBP1), potently inhibited Ad35 infection. Confocal laser scanning microscopy, electron microscopy, and live cell imaging showed that Ad35 colocalized with fluid-phase markers in large endocytic structures that were positive for CD46, alphanu integrins, and also CtBP1. Our results extend earlier observations with HAdV-3 (Ad3) and establish macropinocytosis as an infectious pathway for species B human adenoviruses in epithelial and hematopoietic cells.

Characterization of human adenovirus serotypes 5, 6, 11, and 35 as anticancer agents

Human adenovirus type 5 (Ad5) has been the most popular platform for the development of oncolytic Ads. Alternative Ad serotypes with low seroprevalence might allow for improved anticancer efficacy in Ad5-immune patients. We studied the safety and efficacy of rare serotypes Ad6, Ad11 and Ad35. In vitro cytotoxicity of the Ads correlated with expression of CAR and CD46 in most but not all cell lines. Among CAR-binding viruses, Ad5 was often more active than Ad6, among CD46-binding viruses Ad35 was generally more cytotoxic than Ad11 in cell culture studies. Ad5, Ad6, and Ad11 demonstrated similar anticancer activity in vivo, whereas Ad35 was not efficacious. Hepatotoxicity developed only in Ad5-injected mice. Predosing with Ad11 and Ad35 did not increase infection of hepatocytes with Ad5-based vector demonstrating different interaction of these Ads with Kupffer cells. Data obtained in this study suggest developing Ad6 and Ad11 as alternative Ads for anticancer treatment.