The human HLA-A*0201 allele, expressed in hamster cells, is not a high-affinity receptor for adenovirus type 5 fiber

Baculovirus-assisted Reovirus Infection in Monolayer and Spheroid Cultures of Glioma cells

The mammalian orthoreovirus Type 3 Dearing has great potential as oncolytic agent in cancer therapy. One of the bottlenecks that hampers its antitumour efficacy in vivo is the limited tumour-cell infection and intratumoural distribution. This necessitates strategies to improve tumour penetration. In this study we employ the baculovirus Autographa californica multiple nucleopolyhedrovirus as a tool to expand the reovirus' tropism and to improve its spread in three-dimensional tumour-cell spheroids. We generated a recombinant baculovirus expressing the cellular receptor for reovirus, the Junction Adhesion Molecule-A, on its envelope. Combining these Junction Adhesion Molecule-A-expressing baculoviruses with reovirus particles leads to the formation of biviral complexes. Exposure of the reovirus-resistant glioblastoma cell line U-118 MG to the baculovirus-reovirus complexes results in efficient reovirus infection, high reovirus yields, and significant reovirus-induced cytopathic effects. As compared to the reovirus-only incubations, the biviral complexes demonstrated improved penetration and increased cell killing of three-dimensional U-118 MG tumour spheroids. Our data demonstrate that reovirus can be delivered with increased efficiency into two- and three-dimensional tumour-cell cultures via coupling the reovirus particles to baculovirus. The identification of baculovirus' capacity to penetrate into tumour tissue opens novel opportunities to improve cancer therapy by improved delivery of oncolytic viruses into tumours.

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.

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.

A strategy for adenovirus vector targeting with a secreted single chain antibody

Background

Successful gene therapy will require targeted delivery vectors capable of self-directed localization. In this regard, the use of antibodies or single chain antibody fragments (scFv) in conjunction with adenovirus (Ad) vectors remains an attractive means to achieve cell-specific targeting. However, a longstanding barrier to the development of Ad vectors with genetically incorporated scFvs has been the biosynthetic incompatibility between Ad capsid proteins and antibody-derived species. Specifically, scFv require posttranslational modifications not available to Ad capsid proteins due to their cytoplasmic routing during protein synthesis and virion assembly.

Methodology/Principal Findings

We have therefore sought to develop scFv-targeted Ad vectors using a secreted scFv that undergoes the requisite posttranslational modifications and is trafficked for secretion. Formation of the scFv-targeted Ad vector is achieved via highly specific association of the Ad virion and a targeting scFv employing synthetic leucine zipper-like dimerization domains (zippers) that have been optimized for structural compatibility with the Ad capsid and for association with the secreted scFv. Our results show that zipper-containing Ad fiber molecules trimerize and incorporate into mature virions and that zippers can be genetically fused to scFv without ablating target recognition. Most importantly, we show that zipper-tagged virions and scFv provide target-specific gene transfer.

Conclusions/Significance

This work describes a new approach to produce targeted Ad vectors using a secreted scFv molecule, thereby avoiding the problem of structural and biosynthetic incompatibility between Ad and a complex targeting ligand. This approach may facilitate Ad targeting using a wide variety of targeting ligands directed towards a variety of cellular receptors.

Adenovirus receptors and their implications in gene delivery

Adenoviruses (Ads) have gained popularity as gene delivery vectors for therapeutic and prophylactic applications. Ad entry into host cells involves specific interactions between cell surface receptors and viral capsid proteins. Several cell surface molecules have been identified as receptors for Ad attachment and entry. Tissue tropism of Ad vectors is greatly influenced by their receptor usage. A variety of strategies have been investigated to modify Ad vector tropism by manipulating the receptor-interacting moieties. Many such strategies are aimed at targeting and/or detargeting of Ad vectors. In this review, we discuss the various cell surface molecules that are implicated as receptors for virus attachment and internalization. Special emphasis is given to Ad types that are utilized as gene delivery vectors. Various strategies to modify Ad tropism using the knowledge of Ad receptors are also discussed.

Adenovirus receptors: implications for tropism, treatment and targeting

Adenoviruses (Ads) are the most frequently used viral vectors in gene therapy and cancer therapy. Obstacles to successful clinical application include accumulation of vector and transduction in liver cells, coupled with poor transduction of target cells and tissues such as tumours. Many host molecules, including coagulation factor X, have been identified and suggested to serve as mediators of Ad liver tropism. This review summarises current knowledge concerning these molecules and the mechanisms used by Ads to bind to target cells, and considers the prospects of designing vectors that have been detargeted from the liver and retargeted to cells and tissues of interest in the context of gene therapy and cancer therapy.

Contrasting effects of human, canine, and hybrid adenovirus vectors on the phenotypical and functional maturation of human dendritic cells: implications for clinical efficacy

Antipathogen immune responses create a balance between immunity, tolerance, and immune evasion. However, during gene therapy most viral vectors are delivered in substantial doses and are incapable of expressing gene products that reduce the host's ability to detect transduced cells. Gene transfer efficacy is also modified by the in vivo transduction of dendritic cells (DC), which notably increases the immunogenicity of virions and vector-encoded genes. In this study, we evaluated parameters that are relevant to the use of canine adenovirus serotype 2 (CAV-2) vectors in the clinical setting by assaying their effect on human monocyte-derived DC (hMoDC). We compared CAV-2 to human adenovirus (HAd) vectors containing the wild-type virion, functional deletions in the penton base RGD motif, and the CAV-2 fiber knob. In contrast to the HAd type 5 (HAd5)-based vectors, CAV-2 poorly transduced hMoDC, provoked minimal upregulation of major histocompatibility complex class I/II and costimulatory molecules (CD40, CD80, and CD86), and induced negligible morphological changes indicative of DC maturation. Functional maturation assay results (e.g., reduced antigen uptake; tumor necrosis factor alpha, interleukin-1beta [IL-1beta], gamma interferon [IFN-gamma], IL-10, IL-12, and IFN-alpha/beta secretion; and stimulation of heterologous T-cell proliferation) were also significantly lower for CAV-2. Our data suggested that this was due, in part, to the use of an alternative receptor and a block in vesicular escape. Additionally, HAd5 vector-induced hMoDC maturation was independent of the aforementioned cytokines. Paradoxically, an HAd5/CAV-2 hybrid vector induced the greatest phenotypical and functional maturation of hMoDC. Our data suggest that CAV-2 and the HAd5/CAV-2 vector may be the antithesis of Adenoviridae immunogenicity and that each may have specific clinical advantages.

Adenovirus: from foe to friend

Human adenoviruses (HAdVs) can cause mild respiratory, gastrointestinal, urogenital and ocular disease. Knowledge about HAdVs has been expanding for more than five decades putting them amongst the most-studied viruses. This continued interest stems, to a great extent, from the fact that these double-stranded DNA viruses have proven to be a versatile tool to probe the basic phenomena of eukaryotic cells. HAdV research has led to the discovery of, for instance, RNA splicing and greatly contributed to our knowledge of processes as fundamental as replication, transcription and translation. Moreover, the transformation of rodent cells by HAdVs has provided a system to unravel the molecular pathways that control cell proliferation. As a result, the genetic organisation of these agents is known in great detail allowing the straightforward manipulation of their genomes. In addition, the virus itself became renowned for its ability to produce large amounts of progeny and to efficiently infect mammalian cells regardless of their cell cycle status. These features contributed to the broad use of recombinant HAdVs as gene carriers particularly in in vivo settings where the vast majority of target cells are post-mitotic. The most advanced type of HAdV vectors can accommodate up to 37 kb of foreign DNA and are devoid of viral genes. With the aid of these high-capacity HAdV vectors large physiologically responsive transcriptional elements and/or genes can be efficiently introduced into target cells while minimising adaptive immune responses against the transduced cells. This article provides information on HAdV especially on the aspects pertinent to the design, production and performance of its recombinant forms. The development and characteristics of the main HAdV-based vector types are also briefly reviewed.

Novel Compound Enables High-Level Adenovirus Transduction in the Absence of an Adenovirus-Specific Receptor

Viral vectors are extensively used to deliver foreign DNA to cells for applications ranging from basic research to potential clinical therapies. A limiting step in this process is virus uptake and internalization into the target cells, which is mediated by membrane receptors. Although it is possible to modify viral capsid proteins to target the viruses, such procedures are complex and often unsuccessful. Here we present a rapid, inexpensive system for improving transduction of cells, including those that lack receptors for adenovirus fiber proteins. Addition of GeneJammer (Stratagene, La Jolla, CA) during the adenovirus transduction led to a significant increase in both the total number of transduced cells and the level of transgene expression per cell. Studies using cell lines deficient in adenovirus receptors demonstrated that addition of GeneJammer provided a novel cellular entry mechanism for the virus. These findings were tested in a cell-based gene therapy system for the induction of bone, which is contingent on high-level expression of the transgene. Inclusion of GeneJammer in either Ad5BMP2 or Ad5F35BMP2 transduction of a variety of cells demonstrated a correlating increase in bone formation. The results suggest a novel and versatile method for achieving high-level transduction using adenovirus.

Gene Transfer Mediated by Native versus Fibroblast Growth Factor–Retargeted Adenoviral Vectors into Lung Cancer Cells

We compared native Adenoviral (Ad) vectors to a basic Fibroblast Growth Factor-retargeted Adenovirus (FGF2-Ad) for gene delivery into a diverse panel of lung cancer cells in vitro and xenografts in vivo. Cells were first evaluated for vector-specific receptor expression. Marked variations of surface coxsackie-adenovirus receptor (CAR), but relatively similar levels of alpha v integrin and FGF receptor expression were evident. Transduction efficiency by Ad directly correlated (R = 0.77, 95% CI 0.28-0.94, P = 0.0085) with CAR, but not with alpha v integrin expression. Transduction efficiency by FGF2-Ad did not correlate with the measured FGF receptor expression. Blocking studies indicated that gene transfer by FGF2-Ad occurred by a CAR-independent pathway, and could be inhibited by free FGF in a dose-dependent manner. Ad-antiserum inhibited FGF2-Ad gene transfer, suggesting that the Ad-component was needed for post-entry DNA-delivery. Soluble heparin sulfate proteoglycans (HSPG) or alpha v integrin blockers marginally decreased FGF2-Ad transduction. Both Ad and FGF2-Ad equally transduced CAR-positive non-small cell lung cancer (NSCLC) and small cell lung cancer (SCLC) cells. By contrast, FGF2-Ad had a distinct transduction advantage in CAR-deficient NSCLC cells. This improvement in transduction of CAR-deficient cells by FGF2-Ad persisted in vivo. These data justify the need for an improved FGF2-Ad vector for clinical use in CAR-deficient lung cancer.

Evolution of cell recognition by viruses: a source of biological novelty with medical implications

The picture beginning to form from genome analyses of viruses, unicellular organisms, and multicellular organisms is that viruses have shared functional modules with cells. A process of coevolution has probably involved exchanges of genetic information between cells and viruses for long evolutionary periods. From this point of view present-day viruses show flexibility in receptor usage and a capacity to alter through mutation their receptor recognition specificity. It is possible that for the complex DNA viruses, due to a likely limited tolerance to generalized high mutation rates, modifications in receptor specificity will be less frequent than for RNA viruses, albeit with similar biological consequences once they occur. It is found that different receptors, or allelic forms of one receptor, may be used with different efficiency and receptor affinities are probably modified by mutation and selection. Receptor abundance and its affinity for a virus may modulate not only the efficiency of infection, but also the capacity of the virus to diffuse toward other sites of the organism. The chapter concludes that receptors may be shared by different, unrelated viruses and that one virus may use several receptors and may expand its receptor specificity in ways that, at present, are largely unpredictable.

The Coxsackie-Adenovirus Receptor—A New Receptor in the Immunoglobulin Family Involved in Cell Adhesion

The physiological and cell biological aspects of the Coxsackie-Adenovirus Receptor (CAR) is discussed in this review. The receptor obviously recognizes the group C adenoviruses in vivo, but also fibers from other groups except group B in vitro. The latter viruses seem to utilize a different receptor. The receptor accumulates at, or close to, the tight junction in polarized epithelial cells and probably functions as a cell-cell adhesion molecule. The cytoplasmic tail of the receptor is not required for virus attachment and uptake. Although there is a correlation between CAR and uptake of adenoviruses in several human tumor cells, evidence of an absolute requirement for integrins has not been forthcoming. The implication of these findings for adenovirus gene therapy is discussed.

A recombinant E1-deleted porcine adenovirus-3 as an expression vector

Replication-defective E1-deleted porcine adenoviruses (PAVs) are attractive vectors for vaccination. As a prerequisite for generating PAV-3 vectors containing complete deletion of E1, we transfected VIDO R1 cells (fetal porcine retina cells transformed with E1 region of human adenovirus 5) with a construct containing PAV-3 E1B(large) coding sequences under the control of HCMV promoter. A cell line named VR1BL could be isolated that expressed E1B(large) of PAV-3 and also complemented PAV214 (E1A+E1B(small) deleted). The VR1BL cells could be efficiently transfected with DNA and allowed the rescue and propagation of recombinant PAV507 containing a triple stop codon inserted in the E1B(large) coding sequence. In addition, recombinant PAV227 containing complete deletion of E1 (E1A+E1B(small) + E1B(large)) could be successfully rescued using VR1BL cell line. Recombinant PAV227 replicated as efficiently as wild-type in VR1BL cells but not in VIDO R1 cells, suggesting that E1B(large) was essential for replication of PAV-3. Next, we constructed recombinant PAV219 by inserting green fluorescent (GFP) protein gene flanked by a promoter and a poly(A) in the E1 region of the PAV227 genome. We demonstrated that PAV219 was able to transduce and direct expression of GFP in some human cell lines.

Structural and phylogenetic analysis of adenovirus hexons by use of high-resolution x-ray crystallographic, molecular modeling, and sequence-based methods

A major impediment to the use of adenovirus as a gene therapy vector and for vaccine applications is the host immune response to adenovirus hexon-the major protein component of the icosahedral capsid. A solution may lie in novel vectors with modified or chimeric hexons designed to evade the immune response. To facilitate this approach, we have distinguished the portion of hexon that all serotypes have in common from the hypervariable regions that are responsible for capsid diversity and type-specific immunogenicity. The common hexon core-conserved because it forms the viral capsid-sets boundaries to the regions where modifications can be made to produce nonnative hexons. The core has been defined from the large and diverse set of known hexon sequences by an accurate alignment based on the newly refined crystal structures of human adenovirus types 2 (Ad2) and Ad5 hexon. Comparison of the two hexon models, which are the most accurate so far, reveals that over 90% of the residues in each have three-dimensional positions that closely match. Structures for more distant hexons were predicted by building molecular models of human Ad4, chimpanzee adenovirus (AdC68), and fowl adenovirus 1 (FAV1 or CELO). The five structures were then used to guide the alignment of the 40 full-length (>900 residues) hexon sequences in public databases. Distance- and parsimony-based phylogenetic trees are consistent and reveal evolutionary relationships between adenovirus types that parallel those of their animal hosts. The combination of crystallography, molecular modeling, and phylogenetic analysis defines a conserved molecular core that can serve as the armature for the directed design of novel hexons.

Novel partner proteins of adenovirus penton

Each of the 12 vertices of the adenovirus virion is made of penton, the complex of two oligomeric proteins: a pentameric penton base anchored in the capsid and an antenna-like trimeric fiber extending outwards. Adenovirus penton plays an essential role in the infection of host cells because it is indispensable for virus attachment and internalization. The initial interactions of penton with the primary and secondary receptors are well described. In contrast with that, the role of the penton components downstream of the initial cell contact is not known. This work shows for the first time that two adenovirus structural proteins, fiber and base, are able to interact intimately with different classes of cellular targets. In the case of penton base, a protein responsible for virus internalization, the partners include three ubiquitin-protein ligases that are involved in protein turnover, cell cycle control and endocytosis. Another base protein partner, BAG3, is involved in controlling Hsc70 chaperone activity. Virus attachment protein, fiber, interacts with many different partners, some of them involved in signal transduction and cell growth. Further work will illustrate the implications of these interactions for both the viral and cellular life cycles.

Human adenovirus serotypes 4 and 11 show higher binding affinity and infectivity for endothelial and carcinoma cell lines than serotype 5

Adenoviruses are promising vectors for human cancer gene therapy. However, the extensively used adenoviruses serotypes 2 and 5 (Ad2 and Ad5) from species C have a major disadvantage in being highly prevalent; thus, most adults have an immunity against the two viruses. Furthermore, the expression of coxsackievirus and adenovirus receptors for Ad2 and Ad5 varies in different cells. This study aims to identify adenovirus serotypes with specific tropism for endothelial cells and epithelial tumour cells. Comparison of the binding affinities of Ad31, Ad11, Ad5, Ad37, Ad4 and Ad41, belonging to species A-F, respectively, to established cell lines of hepatoma (HepG2), breast cancer (CAMA and MG7), prostatic cancer (DU145 and LNCaP) and laryngeal cancer (Hep2), as well as to endothelial cells (HMEC), was carried out by flow cytometric analysis. Ad11 from species B showed markedly higher binding affinity than Ad5 for the endothelial cell line and all carcinoma cell lines studied. Ad4 showed a specific binding affinity for hepatoma cells and laryneal carcinoma cells. The ability of Ad11, Ad4 and Ad5 to be expressed in hepatoma, breast cancer and endothelial cell lines was studied by immunostaining and (35)S-labelling of viral proteins in infected cells. Ad11 and Ad4 manifested a higher proportion of infected cells and a higher degree of hexon expression than Ad5.

Recombinant adenovirus-mediated cytotoxic gene therapy of lymphoproliferative disorders: is CAR important for the vector to ride?

The literature has seen an incredible booming of publications related to the use of recombinant adenoviruses as therapeutic tools for lymphoproliferative disorders over the last decade. Several approaches of adenovirus-mediated gene expression have been used to transfect cell lines that are derived from lymphoid tumors and would have otherwise been refractory to other transfection methods. The identification of high-affinity receptor for human adenoviruses serotype 2 and 5, the coxsackie-adenovirus receptor (CAR), has raised the question about its relevance for the efficacy of recombinant adenovirus-mediated gene therapy. We review published studies that have analyzed the use of recombinant adenovirus vectors expressing cytotoxic genes for gene therapy in lymphomas, chronic lymphocytic leukemia and multiple myeloma. For simplicity, we group all these diseases under the term lymphoproliferative disorders. We analyze the use of recombinant adenovirus-mediated cytotoxicity by assessing the importance of the biochemical and intrinsic signaling pathways interacting with the products of the exogenous viral-mediated expression. Ultimately, we discuss studies that have been finalized to by-pass the limitations of the biodistribution of CAR by modifying or targeting adenovirus to other membrane proteins in cells derived from lymphoproliferative disorders.

Adenovirus type 37 binds to cell surface sialic acid through a charge-dependent interaction

Most adenoviruses use the coxsackie-adenovirus receptor (CAR) as a major cellular receptor. We have shown recently that adenovirus types 8, 19a, and 37, which are the major causes of epidemic keratoconjunctivitis, use sialic acid rather than CAR as a major cellular receptor. The predicted isoelectric point of the receptor-interacting knob domain in the adenovirus fiber protein is unusually high (9.0-9.1) in type 8, 19a, and 37. The pKa of sialic acid is low, 2.6, implying a possible involvement of charge in fiber knob-sialic acid interactions. Here we show that (i) positively charged adenovirus knobs require sialic acid for efficient cell membrane interactions; (ii) viral and knob interactions with immobilized sialic acid or cell-surface sialic acid are sensitive to increased ionic strength; (iii) negatively charged molecules such as sulfated glycosaminoglycans inhibit the binding of virions to target cells in a nonspecific, charge-dependent manner; and that (iv) the ability of adenovirus knobs to interact with sialic acid correlates with the overall charge on the top surface of the respective knobs as predicted by homology modeling. Taken together, the results presented provide strong evidence for a charge mechanism during the interaction between the Ad37 fiber knob and sialic acid.

Characterization of E3/49K, a novel, highly glycosylated E3 protein of the epidemic keratoconjunctivitis-causing adenovirus type 19a

The early transcription unit 3 (E3) of human adenoviruses (Ads) encodes proteins with various immunomodulatory functions. Ads from different subgenera differ considerably in their E3 coding capacity, suggesting that distinct sets of immunomodulatory E3 proteins may influence the disease pattern associated with different Ad subgenera. Interestingly, the E3 region of Ads classified in subgenus D, which are often isolated from AIDS patients and have the propensity to cause eye infections, contains a unique gene, named E3/49K, that may encode a protein with a calculated molecular weight of 48,984 that might be implicated in diseases caused by this subgenus. The 49K sequence predicts a highly glycosylated type I transmembrane protein with a short cytoplasmic tail containing two motifs, YXXPhi and LL, potentially involved in targeting the protein to endosomal or lysosomal compartments. Remarkably, the 49K protein is predicted to contain an unusual immunoglobulin-like fold. Here we have characterized the E3/49K protein of Ad type 19a, an Ad of subgenus D which causes epidemic keratoconjunctivitis. E3/49K was synthesized as an 80- to 100-kDa protein, which is unusually large for an E3 protein. In contrast to another early protein, E3/19K, the expression of E3/49K started early but continued throughout the infection cycle. Analysis of the 49K glycosylation revealed that the majority of 49K molecules contained only 12 of the predicted 14 N-glycans. Furthermore, we provide evidence that 49K is O-glycosylated. At steady state, E3/49K was localized in the Golgi-trans-Golgi network and in early endosomes. Interestingly, the 49K protein has a rather short half-life and seems to be proteolytically cleaved. A processing pattern similar to that in the early stages of infection is seen in transfected cells, constitutively expressing 49K in the absence of other Ad proteins. Together, our data provide the first biochemical and cell biological characterization of an unique E3 protein of subgenus D Ads.

N-acetylcysteine augments adenovirus-mediated gene expression in human endothelial cells by enhancing transgene transcription and virus entry

BACKGROUND

It has previously been shown that oxidants reduce the efficiency of adenoviral transduction in human umbilical vein endothelial cells (HUVECs). In this study, the effect of the antioxidant N-acetylcysteine (NAC) in adenovirus-mediated gene transfer has been investigated.

METHODS

HUVECs were pretreated or not with NAC, and infected with E1E3-deleted adenovirus (Ad) containing the LacZ gene expressed from the RSV-LTR promoter/enhancer in the presence and absence of NAC. Transgene expression was assessed at the protein level (histochemical staining, measurement of beta-Gal activity, and western blot), mRNA level (real-time RT-PCR) and gene level (nuclear run on) 24 h and 48 h after infection. Adenoviral DNA was quantitated by real-time PCR, and cell surface expression of Coxsackie/adenovirus receptors (CAR) was determined by FACS analysis.

RESULTS

Pretreatment of cells with NAC prior to Ad infection enhanced beta-Gal activity by two-fold due to an increase in viral DNA, which was related to increased CAR expression. When NAC was present only during the post-infection period, a five-fold increase in beta-Gal activity and LacZ gene transcriptional activity was observed. When NAC was present during both the pretreatment and the post-infection period, beta-Gal activity was further enhanced, by 15-fold. Augmentation of beta-Gal activity was paralleled by an increase in beta-Gal protein and mRNA levels. NAC did not affect the half-life of LacZ mRNA.

CONCLUSION

Pretreatment with NAC prior to Ad infection enhances virus entry, while treatment with NAC post-infection increases transgene transcription. This strategy permits the use of lower adenoviral loads and thus might be helpful for gene therapy of vascular diseases.

Adenovirus type 5 uptake by lung adenocarcinoma cells in culture correlates with Ad5 fibre binding is mediated by alpha(v)beta1 integrin and can be modulated by changes in beta1 integrin function

BACKGROUND

Recombinant adenoviruses (Ad) have been employed as vectors for a wide variety of gene therapy applications, but their use has been hindered by problems relating to efficacy and safety. The efficiency of Ad-mediated gene transfer depends on the interaction of the fibre and penton base proteins with their corresponding cell receptors. Ad infection is initiated by the formation of a high affinity complex between the fibre protein and a host cell protein that for most Ad serotypes is CAR (the coxsackie B virus and Ad receptor). A second molecule, the MHC class I, may also be involved in Ad type 2 and Ad type 5 uptake. Ad internalization results from the interaction of the penton base protein with cell surface integrins alpha(v)beta3 and alpha(v)beta5. In this study, we addressed the interaction between Ad type 5 (Ad5) and its receptors on lung derived adenocarcinoma cells in culture.

METHODS

Using flow cytometry, we determined the level of expression of attachment and internalization receptors that are expressed on the cell surface of A549, H322 and H441 lung-derived adenocarcinoma cells in culture. The level of alpha(v)beta1 cell surface integrin was assessed by immunoprecipitation. Measuring the level of luciferase gene expression at different viral titres quantitated Ad5 uptake by these cells. The kinetics of binding of Ad5 fibre knobs to A549, H322 and H441 cells was assessed in direct binding studies using 125I labelling of purified recombinant Ad5 fibre-knob domains. In order to assess the functionality of integrins, adhesion assays were performed in the presence or absence of activators of integrin function. In competition experiments, prior to exposure to the virus, the cells were pre-incubated with purified recombinant Ad5 fibre-knob domains, function blocking anti-integrin antibodies, or integrin activating agents, prior to the introduction of luciferase expressing Ad5.

RESULTS

We found that Ad5-mediated gene transfer in A549, H322 and H441 adenocarcinoma cells in culture is highly variable and that this variation correlates with specific binding of Ad5 fibre-knob domain binding to the cell surface. We also found, for the first time, that Ad5 infection is mediated by integrin alpha(v)beta1 and that functional activation of beta1 integrin by means of the specific anti-beta1 monoclonal antibody, TS2/16, induced increased A549 cell adhesion to fibronectin and vitronectin and also enhanced Ad5 uptake by these cells.

CONCLUSIONS

Our studies demonstrate that the Ad5 fibre-knob domain interaction with CAR represents a major determinant of Ad5-mediated gene transfer to lung-derived adenocarcinoma cells in culture. The finding that integrin alpha(v)beta1 is involved in Ad5 infection has implications for the use of recombinant Ad5 vectors for cancer gene therapy, since alpha(v)beta1 is expressed at high levels and acts as an alternative vitronectin receptor in many epithelial and some melanoma tumours which express no alpha(v)beta3 and constant low levels of alpha(v)beta5. The fact that the beta1 integrin-activating antibody TS2/16 can enhance alpha(v)beta1-mediated Ad5 infection suggests that the efficacy of Ad5-mediated gene transfer might be influenced not only by the level of cell surface expression of integrins but also by their state of activation.

Trafficking and propagation of canine adenovirus vectors lacking a known integrin-interacting motif

Canine adenovirus type 2 (CAV-2) vectors may be attractive tools for gene transfer thanks to the lack of pre-existing immunity in humans, and because of the preferential transduction of neurons when the vector is injected into the brain and some innervated tissues. The coxsackievirus-adenovirus receptor (CAR) appears to play a major role during infection of most human serotypes, whereas the alpha(v)beta(3/5) integrins have been reported to play a significant auxiliary role. We showed that CAV-2 also attaches to and uses CAR to enter cells, but CAV-2 transduction could be notably different from that of the prototype human adenovirus serotype 5 (Ad5). Initially, the CAV-2 capsid appears to be 10-fold less negatively charged than Ad5. Second, the CAV-2 penton, hexon, and fiber proteins do not contain a known integrin-interacting motif. Because of its potential interest in the clinic, we analyzed the different steps of cellular trafficking and the propagation kinetics of CAV-2 vectors. We found that Ad5 and CAV-2 vectors have comparable kinetics of binding (10 min), internalization (10 min), endosomal escape (17 min), attachment to the nuclear membrane (35 min), and formation (18 hr) and release (34 hr) of functional virions. Surprisingly, the RGD(-) CAV-2 capsid also induced the reorganization of actin filaments in HeLa cells. Actin reorganization is thought to be dependent on alpha(v)beta(3/5) integrin stimulation.

Efficient transduction of murine B lymphocytes and B lymphoma lines by modified adenoviral vectors: enhancement via targeting to FcR and heparan-containing proteins

Murine lymphocytes are relatively refractory to efficient transfection or retroviral gene transduction. Adenovirus has been used as a vector to transduce a wide variety of cell types. Several advantages of adenoviruses are their ability to transduce non-cycling cells and to transduce the majority of cells in a population. Unfortunately, lymphocytes are not susceptible to infection with conventional adenovirus. Therefore, to express genes efficiently in murine B cells, we tested the ability of genetically modified adenovirus to transduce the beta-galactosidase gene. We found that adenovirus containing polylysine in the fiber knob was able to efficiently transduce lipopolysaccharide (LPS)-activated splenic B cells and the B lymphoma line M12.4.1; greater than 80% of the cells expressed beta-galactosidase activity. However, small resting B cells did not express activity unless treated with LPS after infection. This transduction was mediated by interaction with charged molecules since heparan-sulfate, and to a lesser degree chondroitan sulfate, inhibited the transduction. In addition, adenovirus containing a FLAG epitope in the fiber protein was used to target the FcR expressed on B cells using an anti-FLAG antibody. In the presence of anti-FLAG, the modified adenovirus was able to efficiently transduce LPS-activated B cells and several B cell lymphoma lines. Interestingly, in the absence of anti-FLAG, there was low level transduction in the LPS-blasts and in M12.4.1 that was not inhibited by soluble adenovirus fiber protein or agents that block RGD-integrin interactions. These results demonstrate that modified adenovirus efficiently transduce B lymphocytes which will be critical for targeting genes to normal or malignant B cells.

Genetic targeting of an adenovirus vector via replacement of the fiber protein with the phage T4 fibritin

The utility of adenovirus (Ad) vectors for gene therapy is restricted by their inability to selectively transduce disease-affected tissues. This limitation may be overcome by the derivation of vectors capable of interacting with receptors specifically expressed in the target tissue. Previous attempts to alter Ad tropism by genetic modification of the Ad fiber have had limited success due to structural conflicts between the fiber and the targeting ligand. Here we present a strategy to derive an Ad vector with enhanced targeting potential by a radical replacement of the fiber protein in the Ad capsid with a chimeric molecule containing a heterologous trimerization motif and a receptor-binding ligand. Our approach, which capitalized upon the overall structural similarity between the human Ad type 5 (Ad5) fiber and bacteriophage T4 fibritin proteins, has resulted in the generation of a genetically modified Ad5 incorporating chimeric fiber-fibritin proteins targeted to artificial receptor molecules. Gene transfer studies employing this novel viral vector have demonstrated its capacity to efficiently deliver a transgene payload to the target cells in a receptor-specific manner.

Highly efficient transduction of human monocyte-derived dendritic cells with subgroup B fiber-modified adenovirus vectors enhances transgene-encoded antigen presentation to cytotoxic T cells

The efficiency of dendritic cells (DC) as immunotherapeutic vaccines critically depends on optimal delivery of target Ags. Although DC modified by subgroup C type 5 recombinant adenoviruses (rAd5) provide encouraging results, their clinical application is hampered by the need for high viral titers to achieve sufficient gene transfer, due to the lack of the Ad5 fiber receptor. We now demonstrate that rAd5 carrying subgroup B Ad fibers are up to 100-fold more potent than classical rAd5 for gene transfer and expression in human DC, rAd5 with a type 35 fiber (rAd5F35) being the most efficient vector. This improvement relates to a greater and faster virus entry and to an increased transgene expression especially following DC maturation. Furthermore, these new vectors possess enhanced synergistic effects with other activation signals to trigger DC maturation. Consequently, rAd5F35-infected DC engineered to express the gp100 melanoma-associated Ag largely exceed rAd5-infected DC in activating gp100-specific CTL. Finally, the DC infection pattern of rAd5F35 is fully conserved when DC are in the vicinity of primary skin-derived fibroblasts, suggesting this vector as a candidate for in vivo targeting of DC. Thus, subgroup B fiber-modified rAd5 constitute a major breakthrough in the exploitation of ex vivo rAd-targeted DC as clinically relevant vaccines and may also be suitable for in vivo genetic modification of DC.

Adenoviral transduction efficiency of ovarian cancer cells can be limited by loss of integrin beta3 subunit expression and increased by reconstitution of integrin alphavbeta3

Recombinant adenoviruses expressing a therapeutic gene are currently used in clinical studies for treatment of advanced ovarian cancer. We therefore tested whether the expression level of primary (CAR) and secondary adenovirus receptors (integrins) was predictive of the efficacy of adenoviral gene transfer in ovarian cancer cells. Adenoviral transduction efficiency (ATE) was determined with an E1-deleted adenovirus type 5 expressing beta-galactosidase under a CMV promoter (AdGal). ATE was studied in relationship to the expression level of both CAR (coxsackie and adenovirus receptor) and integrins. A representative sample of 25 permanent human cell lines established from advanced ovarian cancer in our laboratory and the OV-2774 cell line were tested. Overall, ATE increased with increasing titers of AdGal. At a given titer of 50 infectious units per cell, transduction efficiency varied from 6 to 94% among the individual cell lines. All cell lines expressed CAR and integrin alpha(v)beta(5), but no relation between ATE and expression level of CAR or alpha(v)beta(5) integrin was observed. In contrast, cell lines with poor ATE, despite expressing high levels of CAR, lacked expression of integrins alpha(v)beta(3) and alpha(5)beta(1). Reconstitution of alpha(v)beta(3) integrin by reexpressing the beta(3) subunit significantly enhanced ATE of ovarian cancer cells. In ovarian cancer, neither integrins nor CAR alone appear to be potentially useful predictive markers for ATE by serotype 5 adenovirus in clinical gene therapy. A minimum level of CAR necessary for binding of adenoviruses was observed in all tested ovarian cancer cell lines. Loss of alpha(v)beta(3) integrin is frequently associated with advanced stages of ovarian cancer and can significantly reduce ATE.

Vascular cell adhesion molecule-1 augments adenovirus-mediated gene transfer

We have reported that adenovirus-mediated gene transfer is augmented in the endothelium of atherosclerotic blood vessels. We observed that vascular cell adhesion molecule-1 (VCAM-1) shares some homology with the coxsackievirus and adenovirus receptor. Because VCAM-1 is upregulated on atherosclerotic endothelial cells, we hypothesized that VCAM-1 may act as an auxiliary receptor to augment adenovirus-mediated gene transfer. To test this hypothesis, stable NIH 3T3 cell lines that constitutively express VCAM-1 on the cell surface were generated. Recombinant adenovirus 5 (Ad5), which contains the reporter ss-galactosidase gene, was used to compare Ad5 infection in VCAM-1(+) and parental NIH 3T3 cells. Total ss-galactosidase activity and the number of transgene-positive cells were 6- to 10-fold and 5-fold higher, respectively, in VCAM-1(+) than in VCAM-1(-) cells. Ad5 binding to VCAM-1(+) cells was increased by 3-fold over VCAM-1(-) cells. Soluble VCAM-1 protein, present during infection or viral binding, reduced ss-galactosidase activity in VCAM-1(+) cells in a dose-dependent manner. Taken together, we conclude that VCAM-1 can mediate adenovirus binding and infection. This may explain, in part, the previous finding that adenovirus-mediated gene transfer is augmented in atherosclerotic arteries.

Manipulation of the cytoplasmic and transmembrane domains alters cell surface levels of the coxsackie-adenovirus receptor and changes the efficiency of adenovirus infection

Expression of the coxsackie-adenovirus receptor (CAR) is a critical determinant in cellular susceptibility to infection with adenovirus-based gene transfer vectors. This study is focused on the hypothesis that manipulation of the cytoplasmic tail and transmembrane regions of CAR can be used to change cell surface levels of CAR and, consequently, to alter the efficiency of Ad-mediated gene transfer. To accomplish this, Flag-tagged ([F]) human CAR ([F]CAR), [F]tailless-CAR (lacking the cytoplasmic tail), and [F]GPI-CAR (containing a GPI lipid anchor instead of the transmembrane and cytoplasmic regions) were exogenously expressed in CHO cells. Analysis of (125)I-labeled anti-Flag antibody binding to transfected cells revealed that [F]tailless-CAR and [F]GPI-CAR were expressed on the cell surface in 1.8- to 2.5-fold higher amounts than [F]CAR, while the total expression levels were similar. Infection with replication-deficient adenovirus encoding beta-galactosidase (Ad-betagal) demonstrated 1.5- to 2-fold higher levels of transgene expression in CHO cells expressing [F]tailless-CAR or [F]GPI-CAR, respectively, compared with cells containing [F]CAR. The form of CAR expressed did not affect the transport of fluorescent Cy3-Ad particles from the cell surface to the nuclear region. These observations indicate that transduction of target cells by Ad vectors can be optimized by increasing cell surface levels of CAR through functional deletion of the tail and membrane protein domains.

Influence of adenoviral fiber mutations on viral encapsidation, infectivity and in vivo tropism

Targeting of adenovirus (Ad)-encoded therapeutic genes to specific cell types has become a major goal in gene therapy. Redirecting the specificity of infection requires the abrogation of the natural interaction between the viral fiber and its cellular receptors (CAR) and the simultaneous introduction of a new binding specificity into the viral capsid. To abrogate the natural affinity of the fiber, we have mutated residues presumed to be directly or indirectly involved in CAR-binding in the knob domain of the fiber protein. These residues are located in the AB loop (Ser408) and in the DG loop (Tyr491, Ala494, Ala503). The mutations Ser408Glu, Tyr491Asp, Ala494Asp and Ala503Asp did not prevent the incorporation of trimeric fibers in the viral capsid but led to loss of CAR binding in vitro. Infectivity of the mutant viruses could be restored in vitro by introducing a ligand at the C-terminal end of the knob, confirming that the reduced infectivity of the fiber-modified virus was due to an impaired interaction of the viral particle with the CAR receptor. However, after systemic delivery, the in vivo biodistribution of impaired CAR-binding viruses without addition of a specific ligand was not altered when compared with wild-type Ad.

A targetable, injectable adenoviral vector for selective gene delivery to pulmonary endothelium in vivo

Adenoviral (Ad) vectors are promising gene therapy vehicles due to their in vivo stability and efficiency, but their potential utility is compromised by their restricted tropism. Targeting strategies have been devised to improve the efficacy of these agents, but specific targeting following in vivo systemic administration of vector has not previously been demonstrated. The distinct aim of the current study was to determine whether an Ad-targeting strategy could maintain fidelity upon systemic vascular administration. We used a bispecific antibody to target Ad infection specifically to angiotensin-converting enzyme (ACE), which is preferentially expressed on pulmonary capillary endothelium and which may thus enable gene therapy for pulmonary vascular disease. Cell-specific gene delivery to ACE-expressing cells was first confirmed in vitro. Administration of retargeted vector complex via tail vein injection into rats resulted in at least a 20-fold increase in both Ad DNA localization and luciferase transgene expression in the lungs, compared to the untargeted vector. Furthermore, targeting led to reduced transgene expression in nontarget organs, especially the liver, where the reduction was over 80%. Immunohistochemical and immunoelectron microscopy analysis confirmed that the pulmonary transgene expression was specifically localized to endothelial cells. Enhancement of transgene expression in the lungs as a result of the ACE-targeting strategy was also confirmed using a new noninvasive imaging technique. This study shows that a retargeting approach can indeed specifically modify the gene delivery properties of an Ad vector given systemically and thus has encouraging implications for the further development of targetable, injectable Ad vectors.

Dependence of adenovirus infectivity on length of the fiber shaft domain

One of the objectives in adenovirus (Ad) vector development is to target gene delivery to specific cell types. Major attention has been given to modification of the Ad fiber knob, which is thought to determine virus tropism. However, among the human Ad serotypes with different tissue tropisms, not only the knob but also the length of the fiber shaft domain varies significantly. In this study we attempted to delineate the role of fiber length in coxsackievirus-adenovirus receptor (CAR)- and non-CAR-mediated infection. A series of Ad serotype 5 (Ad5) capsid-based vectors containing long or short fibers with knob domains derived from Ad5, Ad9, or Ad35 was constructed and tested in adsorption, internalization, and transduction studies. For Ad5 or Ad9 knob-possessing vectors, a long-shafted fiber was critical for efficient adsorption/internalization and transduction of CAR/alphav integrin-expressing cells. Ad5 capids containing short CAR-recognizing fibers were affected in cell adsorption and infection. In contrast, for the chimeric vectors possessing Ad35 knobs, which enter cells by a CAR/alphav integrin-independent pathway, fiber shaft length had no significant influence on binding or infectibility on tested cells. The weak attachment of short-shafted Ad5 or Ad9 knob-possessing vectors seems to be causally associated with a charge-dependent repulsion between Ad5 capsid and acidic cell surface proteins. The differences between short- and long-shafted vectors in attachment or infection were abrogated by preincubation of cells with polycations. This study demonstrates that the fiber-CAR interaction is not the sole determinant for tropism of Ad vectors containing chimeric fibers. CAR- and alphav integrin-mediated infections are influenced by other factors, including the length of the fiber shaft.

Ectodomain of coxsackievirus and adenovirus receptor genetically fused to epidermal growth factor mediates adenovirus targeting to epidermal growth factor receptor-positive cells

Human adenovirus (Ad) is extensively used for a variety of gene therapy applications. However, the utility of Ad vectors is limited due to the low efficiency of Ad-mediated gene transfer to target cells expressing marginal levels of the Ad fiber receptor. Therefore, the present generation of Ad vectors could potentially be improved by modification of Ad tropism to target the virus to specific organs and tissues. The fact that coxsackievirus and adenovirus receptor (CAR) does not play any role in virus internalization, but functions merely as the virus attachment site, suggests that the extracellular part of CAR might be utilized to block the receptor recognition site on the Ad fiber knob domain. We proposed to design bispecific fusion proteins formed by a recombinant soluble form of truncated CAR (sCAR) and a targeting ligand. In this study, we derived sCAR genetically fused with human epidermal growth factor (EGF) and investigated its ability to target Ad infection to the EGF receptor (EGFR) overexpressed on cancer cell lines. We have demonstrated that sCAR-EGF protein is capable of binding to Ad virions and directing them to EGFR, thereby achieving targeted delivery of reporter gene. These results show that sCAR-EGF protein possesses the ability to effectively retarget Ad via a non-CAR pathway, with enhancement of gene transfer efficiency.

Identification of contact residues and definition of the CAR-binding site of adenovirus type 5 fiber protein

The binding of adenovirus (Ad) fiber knob to its cellular receptor, the coxsackievirus and Ad receptor (CAR), promotes virus attachment to cells and is a major determinant of Ad tropism. Analysis of the kinetics of binding of Ad type 5 (Ad5) fiber knob to the soluble extracellular domains of CAR together (sCAR) and each immunoglobulin (Ig) domain (IgV and IgC2) independently by surface plasmon resonance demonstrated that the IgV domain is necessary and sufficient for binding, and no additional membrane components are required to confer high-affinity binding to Ad5 fiber knob. Four Ad5 fiber knob mutations, Ser408Glu and Pro409Lys in the AB loop, Tyr477Ala in the DG loop, and Leu485Lys in beta strand F, effectively abolished high-affinity binding to CAR, while Ala406Lys and Arg412Asp in the AB loop and Arg481Glu in beta strand E significantly reduced the level of binding. Circular dichroism spectroscopy showed that these mutations do not disorder the secondary structure of the protein, implicating Ser408, Pro409, Tyr477, and Leu485 as contact residues, with Ala406, Arg412, and Arg481 being peripherally or indirectly involved in CAR binding. The critical residues have exposed side chains that form a patch on the surface, which thus defines the high-affinity interface for CAR. Additional site-directed mutagenesis of Ad5 fiber knob suggests that the binding site does not extend to the adjacent subunit or toward the edge of the R sheet. These findings have implications for our understanding of the biology of Ad infection, the development of novel Ad vectors for targeted gene therapy, and the construction of peptide inhibitors of Ad infection.

Adenovirus Type 37 Uses Sialic Acid as a Cellular Receptor

Two cellular receptors for adenovirus, coxsackievirus-adenovirus receptor (CAR) and major histocompatibility complex class I (MHC-I) α2, have recently been identified. In the absence of CAR, MHC-I α2 has been suggested to serve as a cellular attachment protein for subgenus C adenoviruses, while members from all subgenera except subgenus B have been shown to interact with CAR. We have found that adenovirus type 37 (Ad37) attachment to CAR-expressing CHO cells was no better than that to CHO cells lacking CAR expression, suggesting that CAR is not used by Ad37 during attachment. Instead, we have identified sialic acid as a third adenovirus receptor moiety. First, Ad37 attachment to both CAR-expresing CHO cells and MHC-I α2-expressing Daudi cells was sensitive to neuraminidase treatment, which eliminates sialic acid on the cell surface. Second, Ad37 attachment to sialic acid-expressing Pro-5 cells was more than 10-fold stronger than that to the Pro-5 subline Lec2, which is deficient in sialic acid expression. Third, neuraminidase treatment of A549 cells caused a 60% decrease in Ad37 replication in a fluorescent-focus assay. Moreover, the receptor sialoconjugate is most probably a glycoprotein rather than a ganglioside, since Ad37 attachment to sialic acid-expressing Pro-5 cells was sensitive to protease treatment. Ad37 attachment to Pro-5 cells occurs via α(2→3)-linked sialic acid saccharides rather than α(2→6)-linked ones, since (i) α(2→3)-specific but not α(2→6)-specific lectins blocked Ad37 attachment to Pro-5 cells and (ii) pretreatment of Pro-5 cells with α(2→3)-specific neuraminidase resulted in decreased Ad37 binding. Taken together, these results suggest that, unlike Ad5, Ad37 makes use of α(2→3)-linked sialic acid saccharides on glycoproteins for entry instead of using CAR or MHC-I α2.

Targeting adenovirus

The use of targeted viral vectors to localize gene transfer to specific cell types holds many advantages over conventional, non-targeted vectors currently used in gene therapy. The resulting improvements in gene localization from targeted adenovirus vectors are likely to reduce immunogenicity and toxicity, increase safety, and enable the systemic administration of these vectors for multiple indications including cancer, cardiovascular disease, and inflammatory disease. Recent advances in the biological understanding of adenovirus structure and adenovirus receptor interactions have fueled the rapid development of targeted adenovirus vectors. Two basic requirements are necessary to create a targeted adenovirus vector: interaction of adenovirus with its native receptors must be removed and novel, tissue-specific ligands must be added to the virus. Two general approaches have been used to achieve these basic requirements. In the 'two-component' approach, a bispecific molecule is complexed with the adenovirus. The bispecific component simultaneously blocks native receptor binding and redirects virus binding to a tissue-specific receptor. In the 'one-component' approach the adenovirus is genetically modified to ablate native receptor interactions and a novel ligand is genetically incorporated into one of the adenovirus coat proteins. Two-component systems offer great flexibility in rapidly validating the feasibility of targeting via a particular receptor. One-component systems offer the best advantages in producing a manufacturable therapeutic and in more completely ablating all native adenovirus receptor interactions. The coming challenges for targeted adenovirus vectors will be the demonstration that the technology performs in vivo. Ultimately, or in parallel, 'receptor-targeting' technology can be combined with improved adenovirus backbones and with 'transcriptional targeting' approaches to create adenovirus which deliver genes selectively, safely, and with little immune response.

Adenovirus type 37 uses sialic acid as a cellular receptor

Two cellular receptors for adenovirus, coxsackievirus-adenovirus receptor (CAR) and major histocompatibility complex class I (MHC-I) alpha2, have recently been identified. In the absence of CAR, MHC-I alpha2 has been suggested to serve as a cellular attachment protein for subgenus C adenoviruses, while members from all subgenera except subgenus B have been shown to interact with CAR. We have found that adenovirus type 37 (Ad37) attachment to CAR-expressing CHO cells was no better than that to CHO cells lacking CAR expression, suggesting that CAR is not used by Ad37 during attachment. Instead, we have identified sialic acid as a third adenovirus receptor moiety. First, Ad37 attachment to both CAR-expressing CHO cells and MHC-I alpha2-expressing Daudi cells was sensitive to neuraminidase treatment, which eliminates sialic acid on the cell surface. Second, Ad37 attachment to sialic acid-expressing Pro-5 cells was more than 10-fold stronger than that to the Pro-5 subline Lec2, which is deficient in sialic acid expression. Third, neuraminidase treatment of A549 cells caused a 60% decrease in Ad37 replication in a fluorescent-focus assay. Moreover, the receptor sialoconjugate is most probably a glycoprotein rather than a ganglioside, since Ad37 attachment to sialic acid-expressing Pro-5 cells was sensitive to protease treatment. Ad37 attachment to Pro-5 cells occurs via alpha(2-->3)-linked sialic acid saccharides rather than alpha(2-->6)-linked ones, since (i) alpha(2-->3)-specific but not alpha(2-->6)-specific lectins blocked Ad37 attachment to Pro-5 cells and (ii) pretreatment of Pro-5 cells with alpha(2-->3)-specific neuraminidase resulted in decreased Ad37 binding. Taken together, these results suggest that, unlike Ad5, Ad37 makes use of alpha(2-->3)-linked sialic acid saccharides on glycoproteins for entry instead of using CAR or MHC-I alpha2.

Adenoviruses activate human dendritic cells without polarization toward a T-helper type 1-inducing subset

Human monocyte-derived dendritic cells (DC) infected with recombinant adenoviruses (rAd) are promising candidate vaccines for inducing protective immunity against pathogens and tumors. However, since some viruses are known to negatively affect DC function, it is important to investigate the interactions between rAd and DC. We now show that infection by rAd enhances the immunostimulatory capacity of immature human monocyte-derived DC through the upregulation of the costimulatory molecules CD80, CD86, and CD40 and the major histocompatibility complex class I and II molecules. Although rAd infection fails to induce the secretion of interleukin-12 (IL-12) and only marginally induces the expression of the DC maturation marker CD83, it acts in synergy with CD40 triggering in rendering DC fully mature. rAd-infected DC triggered through CD40 produce more IL-12 and are more efficient in eliciting T-helper type 1 responses than DC activated by CD40 triggering only. rAd lacking one or more of the early regions, E1, E2A, E3, and E4, which play an important role in virus-host cell interactions are equally capable of DC activation. Efficient DC infection requires a high multiplicity of infection (>1,000), a fact which can be attributed to the absence of the coxsackievirus and adenovirus receptor on this cell type. Despite the poor ability of DC to be infected by rAd, which may be improved by targeting rAd to alternative DC surface molecules, DC infected with all currently tested rAd constitute potent immunostimulators. Our study provides new insights into the interactions between two highly promising vaccine components, rAd and DC, and indicates that their combination into one vaccine may be very advantageous for the stimulation of T-cell immunity.

Mutations in the DG loop of adenovirus type 5 fiber knob protein abolish high-affinity binding to its cellular receptor CAR

The amino acid residues in adenovirus type 5 (Ad5) fiber that interact with its cellular receptor, the coxsackie B virus and Ad receptor (CAR), have not been defined. To investigate this, multiple mutations were constructed in the region between residues 479 and 497 in Ad5 fiber (beta-strands E and F and the adjacent region of the DG loop). The effects of these mutations on binding to CAR were determined by use of cell-binding competition experiments, surface plasmon resonance, and direct binding studies. The mutation effects on the overall folding and secondary structure of the protein were assessed by circular dichroism (CD) spectroscopy. Deletions of two consecutive amino acids between residues 485 and 493 abolished high-affinity binding to CAR; the CD spectra indicated that although there was no disruption of the overall folding and secondary structure of the protein, local conformational changes did occur. Moreover, single site mutations in this region of residues with exposed, surface-accessible side chains, such as Thr492, Asn493, and Val495, had no effect on receptor binding, which demonstrates that these residues are not in contact with CAR themselves. This implies the involvement of residues in neighboring loop regions. Replacement of the segment containing the two very short beta-strands E and F and the turn between them (residues 479 to 486) with the corresponding sequence from Ad3 (betaEFAd3-->5 mutation) resulted in the loss of receptor binding. The identical CD spectra for betaEFAd3-->5 and wild-type proteins suggest that these substitutions caused no conformational rearrangement and that the loss of binding may thus be due to the substitution of one or more critical contact residues. These findings have implications for our understanding of the interaction of Ad5 fiber with CAR and for the construction of targeted recombinant Ad5 vectors for gene therapy purposes.