Identification of CD46 binding sites within the adenovirus serotype 35 fiber knob

Nonclinical characterization of ICVB-1042 as a selective oncolytic adenovirus for solid tumor treatment

ICVB-1042 is an oncolytic adenovirus containing modifications to enhance replication, lysis, and viral spreading in tumor cells. The anti-tumor activity, immune activation, tropism, selectivity, and mechanism of action were evaluated in preparation for a first-in-human study. ICVB-1042 was at least 100-fold more cytotoxic in A549 cells than in normal primary cells tested, demonstrating its high tumor selectivity and a low likelihood of targeting primary tissues. ICVB-1042 administered to mice intravenously or intratumorally was effective in reducing tumor burden. Its intravenous administration also inhibited tumor growth in orthotopic models. ICVB-1042 was well tolerated in mice compared to HAdV-C5 (Wt Ad5), with reduced liver sequestration, supporting safety of the drug for systemic delivery. These preclinical data demonstrating the safety and potency of ICVB-1042 for treatment of various solid tumors support the ongoing clinical investigation (NCT05904236).

The Immune System-A Double-Edged Sword for Adenovirus-Based Therapies

Pathogenic adenovirus (Ad) infections are widespread but typically mild and transient, except in the immunocompromised. As vectors for gene therapy, vaccine, and oncology applications, Ad-based platforms offer advantages, including ease of genetic manipulation, scale of production, and well-established safety profiles, making them attractive tools for therapeutic development. However, the immune system often poses a significant challenge that must be overcome for adenovirus-based therapies to be truly efficacious. Both pre-existing anti-Ad immunity in the population as well as the rapid development of an immune response against engineered adenoviral vectors can have detrimental effects on the downstream impact of an adenovirus-based therapeutic. This review focuses on the different challenges posed, including pre-existing natural immunity and anti-vector immunity induced by a therapeutic, in the context of innate and adaptive immune responses. We summarise different approaches developed with the aim of tackling these problems, as well as their outcomes and potential future applications.

Toward the understanding of DSG2 and CD46 interaction with HAdV-11 fiber, a super-complex analysis

IMPORTANCE

The main limitation of oncolytic vectors is neutralization by blood components, which prevents intratumoral administration to patients. Enadenotucirev, a chimeric HAdV-11p/HAdV-3 adenovirus identified by bio-selection, is a low seroprevalence vector active against a broad range of human carcinoma cell lines. At this stage, there's still some uncertainty about tropism and primary receptor utilization by HAdV-11. However, this information is very important, as it has a direct influence on the effectiveness of HAdV-11-based vectors. The aim of this work is to determine which of the two receptors, DSG2 and CD46, is involved in the attachment of the virus to the host, and what role they play in the early stages of infection.

Oncolytic Adenoviruses Armed with Co-Stimulatory Molecules for Cancer Treatment

In clinical trials, adenovirus vectors (AdVs) are commonly used platforms for human gene delivery therapy. High genome capacity and flexibility in gene organization make HAdVs suitable for cloning. Recent advancements in molecular techniques have influenced the development of genetically engineered adenovirus vectors showing therapeutic potential. Increased molecular understanding of the benefits and limitations of HAdVs in preclinical research and clinical studies is a crucial point in the engineering of refined oncolytic vectors. This review presents HAdV species (A-G) used in oncotherapy. We describe the adenovirus genome organizations and modifications, the possibilities oncolytic viruses offer, and their current limitations. Ongoing and ended clinical trials based on oncolytic adenoviruses are presented. This review provides a broad overview of the current knowledge of oncolytic therapy. HAdV-based strategies targeting tumors by employing variable immune modifiers or delivering immune stimulatory factors are of great promise in the field of immune oncologyy This approach can change the face of the fight against cancer, supplying the medical tools to defeat tumors more selectively and safely.

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.

Ex Vivo and In Vivo CD46 Receptor Utilization by Species D Human Adenovirus Serotype 26 (HAdV26)

Human adenovirus serotype 26 (Ad26) is used as a gene-based vaccine against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and HIV-1. However, its primary receptor portfolio remains controversial, potentially including sialic acid, coxsackie and adenovirus receptor (CAR), integrins, and CD46. We and others have shown that Ad26 can use CD46, but these observations were questioned on the basis of the inability to cocrystallize Ad26 fiber with CD46. Recent work demonstrated that Ad26 binds CD46 with its hexon protein rather than its fiber. We examined the functional consequences of Ad26 for infection in vitro and in vivo. Ectopic expression of human CD46 on Chinese hamster ovary cells increased Ad26 infection significantly. Deletion of the complement control protein domain CCP1 or CCP2 or the serine-threonine-proline (STP) region of CD46 reduced infection. Comparing wild-type and sialic acid-deficient CHO cells, we show that the usage of CD46 is independent of its sialylation status. Ad26 transduction was increased in CD46 transgenic mice after intramuscular (i.m.) injection but not after intranasal (i.n.) administration. Ad26 transduction was 10-fold lower than Ad5 transduction after intratumoral (i.t.) injection of CD46-expressing tumors. Ad26 transduction of liver was 1,000-fold lower than that ofAd5 after intravenous (i.v.) injection. These data demonstrate the use of CD46 by Ad26 in certain situations but also show that the receptor has little consequence by other routes of administration. Finally, i.v. injection of high doses of Ad26 into CD46 mice induced release of liver enzymes into the bloodstream and reduced white blood cell counts but did not induce thrombocytopenia. This suggests that Ad26 virions do not induce direct clotting side effects seen during coronavirus disease 2019 (COVID-19) vaccination with this serotype of adenovirus. IMPORTANCE The human species D Ad26 is being investigated as a low-seroprevalence vector for oncolytic virotherapy and gene-based vaccination against HIV-1 and SARS-CoV-2. However, there is debate in the literature about its tropism and receptor utilization, which directly influence its efficiency for certain applications. This work was aimed at determining which receptor(s) this virus uses for infection and its role in virus biology, vaccine efficacy, and, importantly, vaccine safety.

ChAdOx1 interacts with CAR and PF4 with implications for thrombosis with thrombocytopenia syndrome

Vaccines derived from chimpanzee adenovirus Y25 (ChAdOx1), human adenovirus type 26 (HAdV-D26), and human adenovirus type 5 (HAdV-C5) are critical in combatting the severe acute respiratory coronavirus 2 (SARS-CoV-2) pandemic. As part of the largest vaccination campaign in history, ultrarare side effects not seen in phase 3 trials, including thrombosis with thrombocytopenia syndrome (TTS), a rare condition resembling heparin-induced thrombocytopenia (HIT), have been observed. This study demonstrates that all three adenoviruses deployed as vaccination vectors versus SARS-CoV-2 bind to platelet factor 4 (PF4), a protein implicated in the pathogenesis of HIT. We have determined the structure of the ChAdOx1 viral vector and used it in state-of-the-art computational simulations to demonstrate an electrostatic interaction mechanism with PF4, which was confirmed experimentally by surface plasmon resonance. These data confirm that PF4 is capable of forming stable complexes with clinically relevant adenoviruses, an important step in unraveling the mechanisms underlying TTS.

Oncolytic virotherapy as promising immunotherapy against cancer: mechanisms of resistance to oncolytic viruses

Oncolytic virotherapy has currently emerged as a powerful therapeutic approach in cancer treatment. Although the history of using viruses goes back to the early 20th century, the approval of talimogene laherparepvec (T-VEC) in 2015 increased interest in oncolytic viruses (OVs). OVs are multifaceted biotherapeutic agents because they replicate in and kill tumor cells and augment immune responses by releasing immunostimulatory molecules from lysed cells. Despite promising results, some limitations hinder the efficacy of oncolytic virotherapy. The delivery challenges and the upregulation of checkpoints following oncolytic virotherapy also mediate resistance to OVs by diminishing immune responses. Furthermore, the localization of receptors of viruses in the tight junctions, interferon responses, and the aberrant expression of genes involved in the cell cycle of the virus, including their infection and replication, reduce the efficacy of OVs. In this review, we present different mechanisms of resistance to OVs and strategies to overcome them.

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.

Adenovirus and the Cornea: More Than Meets the Eye

Human adenoviruses cause disease at multiple mucosal sites, including the respiratory, gastrointestinal, and genitourinary tracts, and are common agents of conjunctivitis. One site of infection that has received sparse attention is the cornea, a transparent tissue and the window of the eye. While most adenovirus infections are self-limited, corneal inflammation (keratitis) due to adenovirus can persist or recur for months to years after infection, leading to reduced vision, discomfort, and light sensitivity. Topical corticosteroids effectively suppress late adenovirus keratitis but are associated with vision-threatening side effects. In this short review, we summarize current knowledge on infection of the cornea by adenoviruses, including corneal epithelial cell receptors and determinants of corneal tropism. We briefly discuss mechanisms of stromal keratitis due to adenovirus infection, and review an emerging therapy to mitigate adenovirus corneal infections based on evolving knowledge of corneal epithelial receptor usage.

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.

Diversity within the adenovirus fiber knob hypervariable loops influences primary receptor interactions

Adenovirus based vectors are of increasing importance for wide ranging therapeutic applications. As vaccines, vectors derived from human adenovirus species D serotypes 26 and 48 (HAdV-D26/48) are demonstrating promising efficacy as protective platforms against infectious diseases. Significant clinical progress has been made, yet definitive studies underpinning mechanisms of entry, infection, and receptor usage are currently lacking. Here, we perform structural and biological analysis of the receptor binding fiber-knob protein of HAdV-D26/48, reporting crystal structures, and modelling putative interactions with two previously suggested attachment receptors, CD46 and Coxsackie and Adenovirus Receptor (CAR). We provide evidence of a low affinity interaction with CAR, with modelling suggesting affinity is attenuated through extended, semi-flexible loop structures, providing steric hindrance. Conversely, in silico and in vitro experiments are unable to provide evidence of interaction between HAdV-D26/48 fiber-knob with CD46, or with Desmoglein 2. Our findings provide insight into the cell-virus interactions of HAdV-D26/48, with important implications for the design and engineering of optimised Ad-based therapeutics.

Human adenovirus type 17 from species D transduces endothelial cells and human CD46 is involved in cell entry

More than 70 human adenoviruses with type-dependent pathogenicity have been identified but biological information about the majority of these virus types is scarce. Here we employed multiple sequence alignments and structural information to predict receptor usage for the development of an adenoviral vector with novel biological features. We report the generation of a cloned adenovirus based on human adenovirus type 17 (HAdV17) with high sequence homology to the well characterized human adenovirus type 37 (HAdV37) that causes epidemic keratoconjunctivitis (EKC). Our study revealed that human CD46 (CD46) is involved in cell entry of HAdV17. Moreover, we found that HAdV17 infects endothelial cells (EC) in vitro including primary cells at higher efficiencies compared to the commonly used human adenovirus type 5 (HAdV5). Using a human CD46 transgenic mouse model, we observed that HAdV17 displays a broad tropism in vivo after systemic injection and that it transduces ECs in this mouse model. We conclude that the HAdV17-based vector may provide a novel platform for gene therapy.

Tropism and transduction of oncolytic adenovirus 5 vectors in cancer therapy: Focus on fiber chimerism and mosaicism, hexon and pIX

The cellular internalization (infection of cells) of adenovirus 5 (Ad5) is mediated by the initial attachment of the globular knob domain of the capsid fiber protein to the cell surface coxsackievirus and adenovirus receptor (CAR), then followed by the interaction of the virus penton base proteins with cellular integrins. In tumors, there is a substantial intra- and intertumoral variability in CAR expression. The CAR-negative cells generally exhibit very low infectability. Since the fiber knob is a primary mediator of Ad5 binding to the cell surface, improved infectivity of Ad5-based vectors as oncolytic agents may be achieved via genetic modifications of this domain. The strategies to modify or broaden tropism and increase transduction efficiency of Ad5-based vectors include: 1) an incorporation of a targeting peptide into the fiber knob domain (the HI loop and/or C-terminus); 2) fiber knob serotype switching, or pseudotyping, by constructing chimeric fibers consisting of the knob domain derived from an alternate serotype (e.g., Ad5/3 or Ad5/35 chimeras), which binds to receptor(s) other than CAR (e.g., desmoglein 2/DSG2 and/or CD46); 3) "fiber complex mosaicism", an approach of combining serotype chimerism with peptide ligand(s) incorporation (e.g., Ad5/3-RGD); 4) "dual fiber mosaicism" by expressing two separate fibers with distinct receptor-binding capabilities on the same viral particle (e.g., Ad5-5/3 or Ad5-5/σ1); 5) fiber xenotyping by replacing the knob and shaft domains of wild-type Ad5 fiber protein with fibritin trimerization domain of T4 bacteriophage or σ1 attachment protein of reovirus. Other genetic approaches to increase the CAR-independent transduction efficiency include insertion of a targeting peptide into the hypervariable region of the capsid protein hexon or fusion to the C-terminus of pIX. Finally, we consider a yet unsolved molecular mechanism of liver targeting by Ad5-based vectors (CAR-, integrin-, fiber shaft KKTK motif-, and hepatic heparan sulfate glycosaminoglycans-independent, but fiber-, hexon- and blood factor X-dependent).

Recent Advances in Preclinical Developments Using Adenovirus Hybrid Vectors

Adenovirus (Ad)-based vectors are efficient gene-transfer vehicles to deliver foreign DNA into living organisms, offering large cargo capacity and low immunogenicity and genotoxicity. As Ad shows low integration rates of their genomes into host chromosomes, vector-derived gene expression decreases due to continuous cell cycling in regenerating tissues and dividing cell populations. To overcome this hurdle, adenoviral delivery can be combined with mechanisms leading to maintenance of therapeutic DNA and long-term effects of the desired treatment. Several hybrid Ad vectors (AdV) exploiting various strategies for long-term treatment have been developed and characterized. This review summarizes recent developments of preclinical approaches using hybrid AdVs utilizing either the Sleeping Beauty transposase system for somatic integration into host chromosomes or designer nucleases, including transcription activator-like effector nucleases and clustered regularly interspaced short palindromic repeats/CRISPR-associated protein-9 nuclease for permanent gene editing. Further options on how to optimize these vectors further are discussed, which may lead to future clinical applications of these versatile gene-therapy tools.

Pathogenesis and management of adenoviral keratoconjunctivitis

Human adenovirus (HAdV) is a ubiquitous virus that infects the mucosa of the eye. It is the most common cause of infectious conjunctivitis worldwide, affecting people of all ages and demographics. Pharyngoconjunctival fever outbreak is due to HAdV types 3, 4, and 7, whereas outbreaks of epidemic keratoconjunctivitis are usually caused by HAdV types 8, 19, 37, and 54. Primary cellular receptors, such as CAR, CD46, and sialic acid interact with fiber-knob protein to mediate adenoviral attachment to the host cell, whereas adenoviral penton base–integrin interaction mediates internalization of adenovirus. Type 1 immunoresponse to adenoviral ocular infection involves both innate immunity mediated by natural killer cells and type 1 interferon, as well as adaptive immunity mediated mainly by CD8 T cells. The resulting ocular manifestations are widely variable, with pharyngoconjunctival fever being the most common, manifesting clinically with fever, pharyngitis, and follicular conjunctivitis. Epidemic keratoconjunctivitis, however, is the severest form, with additional involvement of the cornea leading to development of subepithelial infiltrates. Because there is currently no US Food and Drug Administration-approved treatment for adenoviral ocular infection, current management is palliative. The presence of sight-threatening complications following ocular adenoviral infection warrants the necessity for developing antiadenoviral therapy with enhanced therapeutic index. Future trends that focus on adenoviral pathogenesis, including adenoviral protein, which utilize host receptors to promote infection, could be potential therapeutic targets, yielding shorter active disease duration and reduced disease burden.

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.

Targeting oncogenic Ras by the Clostridium perfringens toxin TpeL

Clostridium perfringens toxin TpeL belongs to the family of large clostridial glycosylating toxins. The toxin causes N-acetylglucosaminylation of Ras proteins at threonine35 thereby inactivating the small GTPases. Here, we show that all main types of oncogenic Ras proteins (H-Ras, K-Ras and N-Ras) are modified by the toxin in vitro and in vivo. Toxin-catalyzed modification of Ras was accompanied by inhibition of the MAP kinase pathway. Importantly, TpeL inhibited the paradoxical activation of the MAP kinase pathway induced by the BRAF inhibitor Vemurafenib in the human melanoma cell line SBCL2. The toxin also blocked Ras signaling in a zebrafish embryo model expressing oncogenic H-Ras^G12V, resulting in a reduction of melanocyte number. By using the binding and translocation component of anthrax toxin (protective antigen), the glucosyltransferase domain of TpeL was effectively introduced into target cells that were not sensitive to native TpeL toxin. To reach a higher specificity towards cancer cells, a chimeric TpeL toxin was engineered that possessed the knob region of adenovirus serotype 35 fiber, which interacts with CD46 of target cells frequently overexpressed in cancer cells. The chimeric TpeL fusion toxin efficiently inhibited Ras and MAP kinases in human pancreatic cancer Capan-2 cells, which were insensitive to the wild-type toxin. The data reveal that TpeL and TpeL-related immunotoxins provide a new toolset as Ras-inactivating agents.

Pseudotyped αvβ6 integrin-targeted adenovirus vectors for ovarian cancer therapies

Encouraging results from recent clinical trials are revitalizing the field of oncolytic virotherapies. Human adenovirus type 5 (HAdV-C5/Ad5) is a common vector for its ease of manipulation, high production titers and capacity to transduce multiple cell types. However, effective clinical applications are hindered by poor tumor-selectivity and vector neutralization. We generated Ad5/kn48 by pseudotyping Ad5 with the fiber knob domain from the less seroprevalent HAdV-D48 (Ad48). The vector was shown to utilize coxsackie and adenovirus receptor (CAR) but not CD46 for cell entry. A 20-amino acid peptide NAVPNLRGDLQVLAQKVART (A20) was inserted into the Ad5. Luc HI loop (Ad5.HI.A20) and Ad5/kn48 DG loop (Ad5/kn48.DG.A20) to target a prognostic cancer cell marker, αvβ6 integrin. Relative to the Ad5.Luc parent vector, Ad5.HI.A20, Ad5.KO1.HI.A20 (KO1, ablated CAR-binding) and Ad5/kn48.DG.A20 showed ~ 160-, 270- and 180-fold increased transduction in BT-20 breast carcinoma cells (αvβ6high). Primary human epithelial ovarian cancer (EOC) cultures derived from clinical ascites provided a useful ex vivo model for intraperitoneal virotherapy. Ad5.HI.A20, Ad5.KO1.HI.A20 and Ad5/kn48.DG.A20 transduction was ~ 70-, 60- and 16-fold increased relative to Ad5.Luc in EOC cells (αvβ6high), respectively. A20 vectors transduced EOC cells at up to ~ 950-fold higher efficiency in the presence of neutralizing ovarian ascites, as compared to Ad5.Luc. Efficient transduction and enhanced cancer-selectivity via a non-native αvβ6-mediated route was demonstrated, even in the presence of pre-existing anti-Ad5 immunity. Consequently, αvβ6-targeted Ad vectors may represent a promising platform for local intraperitoneal treatment of ovarian cancer metastases.

A comparative review of viral entry and attachment during large and giant dsDNA virus infections

Viruses enter host cells via several mechanisms, including endocytosis, macropinocytosis, and phagocytosis. They can also fuse at the plasma membrane and can spread within the host via cell-to-cell fusion or syncytia. The mechanism used by a given viral strain depends on its external topology and proteome and the type of cell being entered. This comparative review discusses the cellular attachment receptors and entry pathways of dsDNA viruses belonging to the families Adenoviridae, Baculoviridae, Herpesviridae and nucleocytoplasmic large DNA viruses (NCLDVs) belonging to the families Ascoviridae, Asfarviridae, Iridoviridae, Phycodnaviridae, and Poxviridae, and giant viruses belonging to the families Mimiviridae and Marseilleviridae as well as the proposed families Pandoraviridae and Pithoviridae. Although these viruses have several common features (e.g., topology, replication and protein sequence similarities) they utilize different entry pathways to infect wide-range of hosts, including humans, other mammals, invertebrates, fish, protozoa and algae. Similarities and differences between the entry methods used by these virus families are highlighted, with particular emphasis on viral topology and proteins that mediate viral attachment and entry. Cell types that are frequently used to study viral entry are also reviewed, along with other factors that affect virus-host cell interactions.

Complement Evasion Strategies of Viruses: An Overview

Being a major first line of immune defense, the complement system keeps a constant vigil against viruses. Its ability to recognize large panoply of viruses and virus-infected cells, and trigger the effector pathways, results in neutralization of viruses and killing of the infected cells. This selection pressure exerted by complement on viruses has made them evolve a multitude of countermeasures. These include targeting the recognition molecules for the avoidance of detection, targeting key enzymes and complexes of the complement pathways like C3 convertases and C5b-9 formation - either by encoding complement regulators or by recruiting membrane-bound and soluble host complement regulators, cleaving complement proteins by encoding protease, and inhibiting the synthesis of complement proteins. Additionally, viruses also exploit the complement system for their own benefit. For example, they use complement receptors as well as membrane regulators for cellular entry as well as their spread. Here, we provide an overview on the complement subversion mechanisms adopted by the members of various viral families including Poxviridae, Herpesviridae, Adenoviridae, Flaviviridae, Retroviridae, Picornaviridae, Astroviridae, Togaviridae, Orthomyxoviridae and Paramyxoviridae.

Studies on the Interaction of Tumor-Derived HD5 Alpha Defensins with Adenoviruses and Implications for Oncolytic Adenovirus Therapy

Defensins are small antimicrobial peptides capable of neutralizing human adenovirus (HAdV) in vitro by binding capsid proteins and blocking endosomal escape of virus. In humans, the alpha defensin HD5 is produced by specialized epithelial cells of the gastrointestinal and genito-urinary tracts. Here, we demonstrate, using patient biopsy specimens, that HD5 is also expressed as an active, secreted peptide by epithelial ovarian and lung cancer cells in situ This finding prompted us to study the role of HD5 in infection and spread of replication-competent, oncolytic HAdV type 3 (HAdV3). HAdV3 produces large amounts of penton-dodecahedra (PtDd), virus-like particles, during replication. We have previously shown that PtDd are involved in opening epithelial junctions, thus facilitating lateral spread of de novo-produced virions. Here, we describe a second function of PtDd, namely, the blocking of HD5. A central tool to prove that viral PtDd neutralize HD5 and support spread of progeny virus was an HAdV3 mutant virus in which formation of PtDd was disabled (mut-Ad3GFP, where GFP is green fluorescent protein). We demonstrated that viral spread of mut-Ad3GFP was blocked by synthetic HD5 whereas that of the wild-type (wt) form (wt-Ad3GFP) was only minimally impacted. In human colon cancer Caco-2 cells, induction of cellular HD5 expression by fibroblast growth factor 9 (FGF9) significantly inhibited viral spread and progeny virus production of mut-Ad3GFP but not of wt-Ad3GFP. Finally, the ectopic expression of HD5 in tumor cells diminished the in vivo oncolytic activity of mut-Ad3GFP but not of wt-Ad3GFP. These data suggest a new mechanism of HAdV3 to overcome innate antiviral host responses. Our study has implications for oncolytic adenovirus therapy.IMPORTANCE Previously, it has been reported that human defensin HD5 inactivates specific human adenoviruses by binding to capsid proteins and blocking endosomal escape of virus. The central new findings described in our manuscript are the following: (i) the discovery of a new mechanism used by human adenovirus serotype 3 to overcome innate antiviral host responses that is based on the capacity of HAdV3 to produce subviral penton-dodecahedral particles that act as decoys for HD5, thus preventing the inactivation of virus progeny produced upon replication; (ii) the demonstration that ectopic HD5 expression in cancer cells decreases the oncolytic efficacy of a serotype 5-based adenovirus vector; and (iii) the demonstration that epithelial ovarian and lung cancers express HD5. The study improves our understanding of how adenoviruses establish infection in epithelial tissues and has implications for cancer therapy with oncolytic adenoviruses.

Epithelial Junction Opener Improves Oncolytic Adenovirus Therapy in Mouse Tumor Models

A central resistance mechanism in solid tumors is the maintenance of epithelial junctions between malignant cells that prevent drug penetration into the tumor. Human adenoviruses (Ads) have evolved mechanisms to breach epithelial barriers. For example, during Ad serotype 3 (Ad3) infection of epithelial tumor cells, massive amounts of subviral penton-dodecahedral particles (PtDd) are produced and released from infected cells to trigger the transient opening of epithelial junctions, thus facilitating lateral virus spread. We show here that an Ad3 mutant that is disabled for PtDd production is significantly less effective in killing of epithelial human xenograft tumors than the wild-type Ad3 virus. Intratumoral spread and therapeutic effect of the Ad3 mutant was enhanced by co-administration of a small recombinant protein (JO; produced in Escherichia coli) that incorporated the minimal junction opening domains of PtDd. We then demonstrated that co-administration of JO with replication-competent Ads that do not produce PtDd (Ad5, Ad35) resulted in greater attenuation of tumor growth than virus injection alone. Furthermore, we genetically modified a conditionally replicating Ad5-based oncolytic Ad (Ad5Δ24) to express a secreted form of JO upon replication in tumor cells. The JO-expressing virus had a significantly greater antitumor effect than the unmodified AdΔ24 version. Our findings indicate that epithelial junctions limit the efficacy of oncolytic Ads and that this problem can be address by co-injection or expression of JO. JO has also the potential for improving cancer therapy with other types of oncolytic viruses.

Selection Pressure in the Human Adenovirus Fiber Knob Drives Cell Specificity in Epidemic Keratoconjunctivitis

Human adenoviruses (HAdVs) contain seven species (HAdV-A to -G), each associated with specific disease conditions. Among these, HAdV-D includes those viruses associated with epidemic keratoconjunctivitis (EKC), a severe ocular surface infection. The reasons for corneal tropism for some but not all HAdV-Ds are not known. The fiber protein is a major capsid protein; its C-terminal "knob" mediates binding with host cell receptors to facilitate subsequent viral entry. In a comprehensive phylogenetic analysis of HAdV-D capsid genes, fiber knob gene sequences of HAdV-D types associated with EKC formed a unique clade. By proteotyping analysis, EKC virus-associated fiber knobs were uniquely shared. Comparative structural modeling showed no distinct variations in fiber knobs of EKC types but did show variation among HAdV-Ds in a region overlapping with the known CD46 binding site in HAdV-B. We also found signature amino acid positions that distinguish EKC from non-EKC types, and by in vitro studies we showed that corneal epithelial cell tropism can be predicted by the presence of a lysine or alanine at residue 240. This same amino acid residue in EKC viruses shows evidence for positive selection, suggesting that evolutionary pressure enhances fitness in corneal infection, and may be a molecular determinant in EKC pathogenesis.

IMPORTANCE

Viruses adapt various survival strategies to gain entry into target host cells. Human adenovirus (HAdV) types are associated with distinct disease conditions, yet evidence for connections between genotype and cellular tropism is generally lacking. Here, we provide a structural and evolutionary basis for the association between specific genotypes within HAdV species D and epidemic keratoconjunctivitis, a severe ocular surface infection. We find that HAdV-D fiber genes of major EKC pathogens, specifically the fiber knob gene region, share a distinct phylogenetic clade. Deeper analysis of the fiber gene revealed that evolutionary pressure at crucial amino acid sites has a significant impact on its structural conformation, which is likely important in host cell binding and entry. Specific amino acids in hot spot residues provide a link to ocular cell tropism and possibly to corneal pathogenesis.

Oncolytic Adenovirus: Strategies and Insights for Vector Design and Immuno-Oncolytic Applications

Adenoviruses (Ad) are commonly used both experimentally and clinically, including oncolytic virotherapy applications. In the clinical area, efficacy is frequently hampered by the high rates of neutralizing immunity, estimated as high as 90% in some populations that promote vector clearance and limit bioavailability for tumor targeting following systemic delivery. Active tumor targeting is also hampered by the ubiquitous nature of the Ad5 receptor, hCAR, as well as the lack of highly tumor-selective targeting ligands and suitable targeting strategies. Furthermore, significant off-target interactions between the viral vector and cellular and proteinaceous components of the bloodstream have been documented that promote uptake into non-target cells and determine dose-limiting toxicities. Novel strategies are therefore needed to overcome the obstacles that prevent efficacious Ad deployment for wider clinical applications. The use of less seroprevalent Ad serotypes, non-human serotypes, capsid pseudotyping, chemical shielding and genetic masking by heterologous peptide incorporation are all potential strategies to achieve efficient vector escape from humoral immune recognition. Conversely, selective vector arming with immunostimulatory agents can be utilized to enhance their oncolytic potential by activation of cancer-specific immune responses against the malignant tissues. This review presents recent advantages and pitfalls occurring in the field of adenoviral oncolytic therapies.

Intracellular Signaling and Desmoglein 2 Shedding Triggered by Human Adenoviruses Ad3, Ad14, and Ad14P1

We recently discovered that desmoglein 2 (DSG2) is a receptor for human adenovirus species B serotypes Ad3, Ad7, Ad11, and Ad14. Ad3 is considered to be a widely distributed human pathogen. Ad3 binding to DSG2 triggers the transient opening of epithelial junctions. Here, we further delineate the mechanism that leads to DSG2-mediated epithelial junction opening in cells exposed to Ad3 and recombinant Ad3 fiber proteins. We identified an Ad3 fiber knob-dependent pathway that involves the phosphorylation of mitogen-activated protein (MAP) kinases triggering the activation of the matrix-metalloproteinase ADAM17. ADAM17, in turn, cleaves the extracellular domain of DSG2 that links epithelial cells together. The shed DSG2 domain can be detected in cell culture supernatant and also in serum of mice with established human xenograft tumors. We then extended our studies to Ad14 and Ad14P1. Ad14 is an important research and clinical object because of the recent appearance of a new, more pathogenic strain (Ad14P1). In a human epithelial cancer xenograft model, Ad14P1 showed more efficient viral spread and oncolysis than Ad14. Here, we tested the hypothesis that a mutation in the Ad14P1 fiber knob could account for the differences between the two strains. While our X-ray crystallography studies suggested an altered three-dimensional (3D) structure of the Ad14P1 fiber knob in the F-G loop region, this did not significantly change the fiber knob affinity to DSG2 or the intracellular signaling and DSG2 shedding in epithelial cancer cells.

IMPORTANCE

A number of widely distributed adenoviruses use the epithelial junction protein DSG2 as a receptor for infection and lateral spread. Interaction with DSG2 allows the virus not only to enter cells but also to open epithelial junctions which form a physical barrier to virus spread. Our study elucidates the mechanism beyond virus-triggered junction opening with a focus on adenovirus serotype 3. Ad3 binds to DSG2 with its fiber knob domain and triggers intracellular signaling that culminates in the cleavage of the extracellular domain of DSG2, thereby disrupting DSG2 homodimers between epithelial cells. We confirmed this pathway with a second DSG2-interacting serotype, Ad14, and its recently emerged strain Ad14P1. These new insights in basic adenovirus biology can be employed to develop novel drugs to treat adenovirus infection as well as be used as tools for gene delivery into epithelial tissues or epithelial tumors.

Preclinical safety and efficacy studies with an affinity-enhanced epithelial junction opener and PEGylated liposomal doxorubicin

A central treatment resistance mechanism in solid tumors is the maintenance of epithelial junctions between malignant cells that prevent drug penetration into the tumor. We have developed a small recombinant protein (JO-1) that triggers the transient opening of intercellular junctions and thus increases the efficacy of monoclonal antibodies and chemotherapeutic drugs without causing toxicity in mouse tumor models. Here, we provide data toward the clinical translation of an affinity-enhanced version of JO-1, which we call JO-4, in combination with PEGylated liposomal doxorubicin (PLD)/Doxil for ovarian cancer therapy. We have presented X-ray crystallography data suggesting a structural basis for the higher affinity of JO-4 to DSG2. We also confirmed JO-4 efficacy in a xenograft model with primary ovarian cancer cells showing that JO-4 can salvage Doxil therapy when given at a dose that was threefold lower than the therapeutic dose. Furthermore, we tested the safety of intravenous JO-4 alone and in combination with Doxil in Macaca fascicularis, an adequate animal model for predicting toxicity in humans. Our studies did not show critical JO-4-related toxicity or an increase of Doxil-related side effects. Our efficacy and safety data will help to support an Investigational new drug-filing for a JO-4/Doxil combination treatment.

Tumor Restrictions to Oncolytic Virus

Oncolytic virotherapy has advanced since the days of its conception but therapeutic efficacy in the clinics does not seem to reach the same level as in animal models. One reason is premature oncolytic virus clearance in humans, which is a reasonable assumption considering the immune-stimulating nature of the oncolytic agents. However, several studies are beginning to reveal layers of restriction to oncolytic virotherapy that are present before an adaptive neutralizing immune response. Some of these barriers are present constitutively halting infection before it even begins, whereas others are raised by minute cues triggered by virus infection. Indeed, we and others have noticed that delivering viruses to tumors may not be the biggest obstacle to successful therapy, but instead the physical make-up of the tumor and its capacity to mount antiviral defenses seem to be the most important efficacy determinants. In this review, we summarize the constitutive and innate barriers to oncolytic virotherapy and discuss strategies to overcome them.

CD46-mediated transduction of a species D adenovirus vaccine improves mucosal vaccine efficacy

The high levels of preexisting immunity against Adenovirus type 5 (Ad5) have deemed Ad5 unusable for translation as a human vaccine vector. Low seroprevalent alternative viral vectors may be less impacted by preexisting immunity, but they may also have significantly different phenotypes from that of Ad5. In this study we compare species D Ads (26, 28, and 48) to the species C Ad5. In vitro transduction studies show striking differences between the species C and D viruses. Most notably, Ad26 transduced human dendritic cells much more effectively than Ad5. In vivo imaging studies showed strikingly different transgene expression profiles. The Ad5 virus was superior to the species D viruses in BALB/c mice when delivered intramuscularly. However, the inverse was true when the viruses were delivered mucosally via the intranasal epithelia. Intramuscular transduction was restored in mice that ubiquitously expressed human CD46, the primary receptor for species D viruses. We analyzed both species C and D Ads for their ability to induce prophylactic immunity against influenza in the CD46 transgenic mouse model. Surprisingly, the species D vaccines again failed to induce greater levels of protective immunity as compared with the species C Ad5 when delivered intramuscularly. However, the species D Ad vaccine vector, Ad48, induced significantly greater protection as compared with Ad5 when delivered mucosally via the intranasal route in CD46 transgenic mice. These data shed light on the complexities between the species and types of Ad. Our findings indicate that more research will be required to identify the mechanisms that play a key role in the induction of protective immunity induced by species D Ad vaccines.

Protein engineering to target complement evasion in cancer

The complement system is composed of soluble factors in plasma that enhance or "complement" immune-mediated killing through innate and adaptive mechanisms. Activation of complement causes recruitment of immune cells; opsonization of coated cells; and direct killing of affected cells through a membrane attack complex (MAC). Tumor cells up-regulate complement inhibitory factors - one of several strategies to evade the immune system. In many cases as the tumor progresses, dramatic increases in complement inhibitory factors are found on these cells. This review focuses on the classic complement pathway and the role of major complement inhibitory factors in cancer immune evasion as well as on how current protein engineering efforts are being employed to increase complement fixing or to reverse complement resistance leading to better therapeutic outcomes in oncology. Strategies discussed include engineering of antibodies to enhance complement fixation, antibodies that neutralize complement inhibitory proteins as well as engineered constructs that specifically target inhibition of the complement system.

Bridging the past and the future of virology: surface plasmon resonance as a powerful tool to investigate virus/host interactions

Despite decades of antiviral drug research and development, viruses still remain a top global healthcare problem. Compared to eukaryotic cells, viruses are composed by a limited numbers of proteins that, nevertheless, set up multiple interactions with cellular components, allowing the virus to take control of the infected cell. Each virus/host interaction can be considered as a therapeutical target for new antiviral drugs but, unfortunately, the systematic study of a so huge number of interactions is time-consuming and expensive, calling for models overcoming these drawbacks. Surface plasmon resonance (SPR) is a label-free optical technique to study biomolecular interactions in real time by detecting reflected light from a prism-gold film interface. Launched 20 years ago, SPR has become a nearly irreplaceable technology for the study of biomolecular interactions. Accordingly, SPR is increasingly used in the field of virology, spanning from the study of biological interactions to the identification of putative antiviral drugs. From the literature available, SPR emerges as an ideal link between conventional biological experimentation and system biology studies functional to the identification of highly connected viral or host proteins that act as nodal points in virus life cycle and thus considerable as therapeutical targets for the development of innovative antiviral strategies.

Pseudotyping the adenovirus serotype 5 capsid with both the fibre and penton of serotype 35 enhances vascular smooth muscle cell transduction

Ex vivo gene therapy during coronary artery bypass grafting (CABG) holds great potential to prevent excessive smooth muscle cell (SMC) proliferation, neointima formation and graft failure. The most successful preclinical strategies to date have utilised vectors based on the species C adenovirus, Ad5, which engages the Coxsackie and Adenovirus receptor (CAR) as its primary attachment receptor. Profiling receptors on human SMCs demonstrated the absence of CAR but substantial expression of the species B receptor CD46. We performed transduction experiments using Ad5 and the CD46-utilising adenovirus Ad35, and found Ad35 significantly more efficient at transducing SMCs. To evaluate whether transduction could be further augmented, we evaluated chimeric CD46-utilising Ad5/Ad35 vectors comprising the Ad5 capsid pseudotyped with the Ad35 fibre alone (Ad5/F35) or in combination with the Ad35 penton (Ad5/F35/P35). In human smooth muscle cells (hSMCs), Ad5/F35/P35 mediated significantly higher levels of transduction than either parental vector or Ad5/F35. Ex vivo transduction experiments using mouse aortas from CD46 transgenics demonstrated that Ad5/F35/P35 was significantly more efficient at transducing SMCs than the other vectors tested. Finally, ex vivo transduction and immunofluorescent colocalisation experiments using human tissue from CABG procedures confirmed the preclinical potential of Ad5/F35/P35 as an efficient vector for vascular transduction during CABG.

Structural and functional studies on the interaction of adenovirus fiber knobs and desmoglein 2

Human adenovirus (Ad) serotypes Ad3, Ad7, Ad11, and Ad14, as well as a recently emerged strain of Ad14 (Ad14p1), use the epithelial junction protein desmoglein 2 (DSG2) as a receptor for infection. Unlike Ad interaction with CAR and CD46, structural details for Ad binding to DSG2 are still elusive. Using an approach based on Escherichia coli expression libraries of random Ad3 and Ad14p1 fiber knob mutants, we identified amino acid residues that, when mutated individually, ablated or reduced Ad knob binding to DSG2. These residues formed three clusters inside one groove at the extreme distal end of the fiber knob. The Ad3 fiber knob mutant library was also used to identify variants with increased affinity to DSG2. We found a number of mutations within or near the EF loop of the Ad3 knob that resulted in affinities to DSG2 that were several orders of magnitude higher than those to the wild-type Ad3 knob. Crystal structure analysis of one of the mutants showed that the introduced mutations make the EF loop more flexible, which might facilitate the interaction with DSG2. Our findings have practical relevance for cancer therapy. We have recently reported that an Ad3 fiber knob-containing recombinant protein (JO-1) is able to trigger opening of junctions between epithelial cancer cells which, in turn, greatly improved the intratumoral penetration and efficacy of therapeutic agents (I. Beyer, et al., Clin. Cancer Res. 18:3340-3351, 2012; I. Beyer, et al., Cancer Res. 71:7080-7090, 2011). Here, we show that affinity-enhanced versions of JO-1 are therapeutically more potent than the parental protein in a series of cancer models.

Conserved fiber-penton base interaction revealed by nearly atomic resolution cryo-electron microscopy of the structure of adenovirus provides insight into receptor interaction

Adenovirus (Ad) cell attachment is initiated by the attachment of the fiber protein to a primary receptor (usually CAR or CD46). This event is followed by the engagement of the penton base protein with a secondary receptor (integrin) via its loop region, which contains an Arg-Gly-Asp (RGD) motif, to trigger virus internalization. To understand the well-orchestrated adenovirus cell attachment process that involves the fiber and the penton base, we reconstructed the structure of an Ad5F35 capsid, comprising an adenovirus type 5 (Ad5) capsid pseudotyped with an Ad35 fiber, at a resolution of approximately 4.2 Å. The fiber-penton base interaction in the cryo-electron microscopic (cryo-EM) structure of Ad5F35 is similar to that in the cryo-EM structure of Ad5, indicating that the fiber-penton base interaction of adenovirus is conserved. Our structure also confirms that the C-terminal segment of the fiber tail domain constitutes the bottom trunk of the fiber shaft. Based on the conserved fiber-penton base interaction, we have proposed a model for the interaction of Ad5F35 with its primary and secondary receptors. This model could provide insight for designing adenovirus gene delivery vectors.

Latest insights on adenovirus structure and assembly

Adenovirus (AdV) capsid organization is considerably complex, not only because of its large size (~950 Å) and triangulation number (pseudo T = 25), but also because it contains four types of minor proteins in specialized locations modulating the quasi-equivalent icosahedral interactions. Up until 2009, only its major components (hexon, penton, and fiber) had separately been described in atomic detail. Their relationships within the virion, and the location of minor coat proteins, were inferred from combining the known crystal structures with increasingly more detailed cryo-electron microscopy (cryoEM) maps. There was no structural information on assembly intermediates. Later on that year, two reports described the structural differences between the mature and immature adenoviral particle, starting to shed light on the different stages of viral assembly, and giving further insights into the roles of core and minor coat proteins during morphogenesis [1,2]. Finally, in 2010, two papers describing the atomic resolution structure of the complete virion appeared [3,4]. These reports represent a veritable tour de force for two structural biology techniques: X-ray crystallography and cryoEM, as this is the largest macromolecular complex solved at high resolution by either of them. In particular, the cryoEM analysis provided an unprecedented clear picture of the complex protein networks shaping the icosahedral shell. Here I review these latest developments in the field of AdV structural studies.

Attenuation of CD4+ T-cell function by human adenovirus type 35 is mediated by the knob protein

The complement-regulatory protein CD46 is the primary receptor for human adenovirus type 35 (HAdV-35) and can regulate human immune-cell activation. CD4(+) T-cells are critical for initiating and maintaining adaptive immunity elicited by infection or vaccination. It was reported previously that HAdV-35 can bind these cells and suppress their activation. The data reported here demonstrate that recombinant trimeric HAdV-35 knob proteins alone can induce CD46 receptor downregulation and inhibit interleukin-2 production and proliferation of human CD4(+) T-cells in vitro similarly to mAbs specific to the CD46 region bound by HAdV-35 knobs. A mutant knob protein with increased affinity for CD46 compared with the wild-type knob caused equivalent effects. In contrast, a CD46-binding-deficient mutant knob protein did not inhibit T-cell activation. Thus, the capacity of HAdV-35 to attenuate human CD4(+) T-cell activation depends predominantly on knob interactions with CD46 and can occur independently of infection.

Avidity binding of human adenovirus serotypes 3 and 7 to the membrane cofactor CD46 triggers infection

The species B human adenoviruses (HAdVs) infect cells upon attaching to CD46 or desmoglein 2 (DSG-2) by one or several of their 12 fiber knob trimers (FKs). To test whether DSG-2 and CD46 simultaneously serve as virus receptors for adenovirus type 3 (Ad3), we performed individual and combined CD46/DSG-2 loss-of-function studies in human lung A549 and 16HBE14o cells. Our results suggest that in these cells, DSG-2 functions as a major attachment receptor for Ad3, whereas CD46 exerts a minor contribution to virus attachment and uptake in the range of ∼10%. However, in other cells the role of CD46 may be more pronounced depending on, e.g., the expression levels of the receptors. To test if avidity allows Ad3/7 to use CD46 as a receptor, we performed gain-of-function studies. The cell surface levels of ectopically expressed CD46 in CHO or human M010119 melanoma cells lacking DSG-2 positively correlated with Ad3/7 infections, while Ad11/35 infections depended on CD46 but less on CD46 levels. Antibody-cross-linked soluble CD46 blocked Ad3/7/11/35 infections, while soluble CD46 alone blocked Ad11/35 but not Ad3/7. Soluble Ad3/7-FKs poorly inhibited Ad3/7 infection of CHO-CD46 cells, illustrating that Ad3/7-FKs bind with low affinity to CD46. This was confirmed by Biacore studies. Ad3/7-FK binding to immobilized CD46 at low density was not detected, unlike that of Ad11/35-FK. At higher CD46 densities, however, Ad3/7-FK bound to CD46 with only 15-fold-higher dissociation constants than those of Ad11/35-FK. These data show that an avidity mechanism for Ad3/7 binding to CD46 leads to infection of CD46-positive cells.

Adenovirus with hexon Tat-protein transduction domain modification exhibits increased therapeutic effect in experimental neuroblastoma and neuroendocrine tumors

Adenovirus serotype 5 (Ad5) is widely used as an oncolytic agent for cancer therapy. However, its infectivity is highly dependent on the expression level of coxsackievirus-adenovirus receptor (CAR) on the surfaces of tumor cells. Furthermore, infected cells overproduce adenovirus fiber proteins, which are released prior to cell lysis. The released fibers block CAR on noninfected neighboring cells, thereby preventing progeny virus entry. Our aim was to add a CAR-independent infection route to Ad5 to increase the infectivity of tumor cells with low CAR expression and prevent the fiber-masking problem. We constructed Ad5 viruses that encode the protein transduction domain (PTD) of the HIV-1 Tat protein (Tat-PTD) in hypervariable region 5 (HVR5) of the hexon protein. Tat-PTD functions as a cell-penetrating peptide, and Tat-PTD-modified Ad5 showed a dramatic increased transduction of CAR-negative cell lines compared to unmodified vector. Moreover, while tumor cell infectivity was severely reduced for Ad5 in the presence of fiber proteins, it was only marginally reduced for Tat-PTD-modified Ad5. Furthermore, because of the sequence alteration in the hexon HVR, coagulation factor X-mediated virus uptake was significantly reduced. Mice harboring human neuroblastoma and neuroendocrine tumors show suppressed tumor growths and prolonged survival when treated with Tat-PTD-modified oncolytic viruses. Our data suggest that modification of Ad5 with Tat-PTD in HVR5 expands its utility as an oncolytic agent.

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.

Adenovirus type-35 vectors block human CD4+ T-cell activation via CD46 ligation

Recombinant adenoviruses (rAds) based on types 5 (rAd5) and 35 (rAd35) have emerged as important vaccine delivery vectors in clinical testing for a variety of pathogens. A major difference between these vectors is their binding to cellular receptors used for infection. Whereas rAd5 binds coxsackie-adenovirus receptor (CAR), rAd35 binds the complement regulatory protein CD46. Although rAd35 infected and phenotypically matured human blood dendritic cells (DCs) more efficiently than rAd5, we show here that rAd35 markedly suppressed DC-induced activation of naive CD4(+) T cells. rAd35 specifically blocked both DCs and anti-CD3/CD28 mAb-induced naive T-cell proliferation and IL-2 production. This effect was also observed in CD4(+) memory T cells but to a lesser extent. The suppression occurred by rAd35 binding to CD46 on T cells and was independent of infection. CD46 engagement with mAb mimicked the effects of rAd35 and also led to deficient NF-κB nuclear translocation. In contrast, rAd5 and rAd35 vectors with ablated CD46 binding did not inhibit T-cell activation. Our findings provide insights into the basic biology of adenoviruses and indicate that CD46 binding may have an impact on the generation of primary CD4(+) T-cell responses by Ad35.

Oncolytic adenovirus modified with somatostatin motifs for selective infection of neuroendocrine tumor cells

We have previously described the oncolytic adenovirus, Ad(CgA-E1A-miR122), herein denoted Ad5(CgA-E1A-miR122) that selectively replicates in and kills neuroendocrine cells, including freshly isolated midgut carcinoid cells from liver metastases. Ad5(CgA-E1A-miR122) is based on human adenovirus serotype 5 (Ad5) and infects target cells by binding to the coxsackie-adenovirus receptor (CAR) and integrins on the cell surface. Some neuroendocrine tumor (NET) and neuroblastoma cells express low levels of CAR and are therefore poorly transduced by Ad5. However, they often express high levels of somatostatin receptors (SSTRs). Therefore, we introduced cyclic peptides, which contain four amino acids (FWKT) and mimic the binding site for SSTRs in the virus fiber knob. We show that FWKT-modified Ad5 binds to SSTR₂ on NET cells and transduces midgut carcinoid cells from liver metastases about 3-4 times better than non-modified Ad5. Moreover, FWKT-modified Ad5 overcomes neutralization in an ex vivo human blood loop model to greater extent than Ad5, indicating that fiber knob modification may prolong the systemic circulation time. We conclude that modification of adenovirus with the FWKT motif may be beneficial for NET therapy.

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.

Virus–complement interactions: an assiduous struggle for dominance

The complement system is a major component of the innate immune system that recognizes invading pathogens and eliminates them by means of an array of effector mechanisms, in addition to using direct lytic destruction. Viruses, in spite of their small size and simple composition, are also deftly recognized and neutralized by the complement system. In turn, as a result of years of coevolution with the host, viruses have developed multiple mechanisms to evade the host complement. These complex interactions between the complement system and viruses have been an area of focus for over three decades. In this article, we provide a broad overview of the field using key examples and up-to-date information on the complement-evasion strategies of viruses.

Adenovirus 11p downregulates CD46 early in infection

Adenovirus 11 prototype (Ad11p), belonging to species B, uses CD46 as an attachment receptor. CD46, a complement regulatory molecule, is expressed on all human nucleated cells. We show here that Ad11p virions downregulate CD46 on the surface of K562 cells as early as 5min p.i. Specific binding to CD46 by the Ad11p fiber knob was required to mediate downregulation. The complement regulatory factors CD55 and CD59 were also reduced to a significant extent as a consequence of Ad11p binding to K562 cells. In contrast, binding of Ad7p did not result in downregulation of CD46 early in infection. Thus, the presumed interaction between Ad7p and CD46 did not have the same consequences as the Ad11p-CD46 interaction, the latter virus (Ad11p) being a promising gene therapy vector candidate. These findings may lead to a better understanding of the pathogenesis of species B adenovirus infections.

Infection and killing of multiple myeloma by adenoviruses

Oncolytic virotherapy makes use of the natural ability of viruses to infect and kill cancer cells. Adenovirus serotype 5 (Ad5) has been approved for use in humans as a therapy for solid cancers. In this study, we have tested whether Ad5 and low-seroprevalence adenoviruses can be used as oncolytics for multiple myeloma (MM). We show that Ad5 productively infects most myeloma cell lines, replicates to various degrees, and mediates oncolytic cell killing in vitro and in vivo. Comparison of Ad5 with low-seroprevalence Ads on primary marrow samples from MM patients revealed striking differences in the abilities of different adenoviral serotypes to kill normal CD138(-) cells and CD138(+) MM cells. Ad5 and Ad6 from species C and Ad26 and Ad48 from species D all mediated killing of CD138(+) cells with low-level killing of CD138(-) cells. In contrast, Ad11, Ad35, Ad40, and Ad41 mediated weak oncolytic effects in all of the cells. Comparison of cell binding, cell entry, and replication revealed that Ad11 and Ad35 bound MM cells 10 to 100 times better than other serotypes. However, after this efficient interaction, Ad11 and Ad35 viral DNA was not replicated and cell killing did not occur. In contrast, Ad5, Ad6, Ad26, and Ad48 all replicated 10- to 100-fold in MM cells and this correlated with cell killing. These data suggest that Ad5 and other low-seroprevalence adenoviruses may have utility as oncolytic agents against MM and other hematologic malignancies.

Structure of adenovirus type 21 knob in complex with CD46 reveals key differences in receptor contacts among species B adenoviruses

The complement regulation protein CD46 is the primary attachment receptor for most species B adenoviruses (Ads). However, significant variability exists in sequence and structure among species B Ads in the CD46-binding regions, correlating with differences in affinity. Here, we report a structure-function analysis of the interaction of the species B Ad21 knob with the two N-terminal repeats SCR1 and SCR2 of CD46, CD46-D2. We have determined the structures of the Ad21 knob in its unliganded form as well as in complex with CD46-D2, and we compare the interactions with those observed for the Ad11 knob-CD46-D2 complex. Surface plasmon resonance measurements demonstrate that the affinity of Ad21 knobs for CD46-D2 is 22-fold lower than that of the Ad11 knob. The superposition of the Ad21 and Ad11 knob structures in complex with CD46-D2 reveals a substantially different binding mode, providing an explanation for the weaker binding affinity of the Ad21 knob for its receptor. A critical difference in both complex structures is that a key interaction point, the DG loop, protrudes more in the Ad21 knob than in the Ad11 knob. Therefore, the protruding DG loop does not allow CD46-D2 to approach the core of the Ad21 knob as closely as in the Ad11 knob-CD46-D2 complex. In addition, the engagement of CD46-D2 induces a conformational change in the DG loop in the Ad21 knob but not in the Ad11 knob. Our results contribute to a more profound understanding of the CD46-binding mechanism of species B Ads and have relevance for the design of more efficient gene delivery vectors.

Selective transduction of mature DC in human skin and lymph nodes by CD80/CD86-targeted fiber-modified adenovirus-5/3

In vivo targeting of dendritic cells (DC) represents an attractive alternative to currently apply ex vivo DC-based genetic tumor vaccination protocols. Finding the optimal vector for in vivo targeting of DC is important for such strategies. We, therefore, tested a panel of subgroup C/B chimeric and fiber-modified adenoviruses (Ads) for their relative capacity to transduce human DC. We made use of in vitro generated Langerhans cells, and of ex vivo human skin and melanoma-draining lymph node derived DC. Of the tested viruses the C/B-chimeric adenovirus serotype 5 (Ad5)/3 virus most efficiently transduced in vitro generated Langerhans cells. In addition, Ad5/3 preferentially targeted mature myeloid DC from human skin and draining lymph node and transduced them at significantly higher frequencies than Ad5. In addition, Ad5/3 was more specific for mature human skin-derived CD1a+ CD83+ DC than the previously reported DC-transducing C/B-chimeric vector Ad5/35, infecting less bystander cells. It was previously reported that Ad5/3 transduced human monocyte-derived DC by binding to the B7 molecules CD80 and CD86. High-efficiency transduction of mature skin-derived DC was similarly shown to be mediated through binding to CD80/CD86 and not to interfere with subsequent T-cell priming. We conclude that Ad5/3, in combination with DC-activating adjuvants, represents a promising therapeutic tool for the in vivo transduction of mature DC, and may be less likely to induce unwanted side effects such as immune tolerance through the infection of nonprofessional antigen-presenting cells.