A human cell line selected for resistance to adenovirus infection has reduced levels of the virus receptor

Virus-Receptor Interactions: Structural Insights For Oncolytic Virus Development

Recent advancements in oncolytic virotherapy commend a special attention to developing new strategies for targeting cancer cells with oncolytic viruses (OVs). Modifications of the viral envelope or coat proteins serve as a logical mean of repurposing viruses for cancer treatment. In this review, we discuss how detailed structural knowledge of the interactions between OVs and their natural receptors provide valuable insights into tumor specificity of some viruses and re-targeting of alternate receptors for broad tumor tropism or improved tumor selectivity.

Novel Divergent Polar Bear-Associated Mastadenovirus Recovered from a Deceased Juvenile Polar Bear

Cross-species transmission of viral pathogens is becoming an increasing problem for captive-animal facilities. This study highlights how animals in captivity are vulnerable to novel opportunistic pathogens, many of which do not result in straightforward diagnosis from symptoms and histopathology. In this study, a novel pathogen was suspected to have contributed to the death of a juvenile polar bear. HTS techniques were employed, and a novel Mastadenovirus was isolated. The virus was present in both the tissue and blood samples. Phylogenetic analysis of the virus at both the gene and genome levels revealed that it is highly divergent to other known mastadenoviruses. Overall, this study shows that animals in isolated conditions still come into contact with novel pathogens, and for many of these pathogens, the host reservoir and mode of transmission are yet to be determined.

Polar bears in captivity can be exposed to opportunistic pathogens not present in their natural environments. A 4-month-old polar bear (Ursus maritimus) living in an isolated enclosure with his mother in the Tierpark Berlin, Berlin, Germany, was suffering from severe abdominal pain, mild diarrhea, and loss of appetite and died in early 2017. Histopathology revealed severe hepatic degeneration and necrosis without evidence of inflammation or inclusion bodies, although a viral infection had been suspected on the basis of the clinical signs. We searched for nucleic acids of pathogens by shotgun high-throughput sequencing (HTS) from genomic DNA and cDNA extracted from tissue and blood. We identified a novel Mastadenovirus and assembled a nearly complete genome from the shotgun sequences. Quantitative PCR (qPCR) revealed that viral DNA was present in various concentrations in all tissues examined and that the highest concentrations were found in blood. Viral culture did not yield cytopathic effects, but qPCR suggested that virus replication was sustained for up to three passages. Positive immunofluorescence staining confirmed that the virus was able to replicate in the cells during early passage. Phylogenetic analysis demonstrated that the virus is highly divergent compared to other previously identified Mastadenovirus members and basal to most known viral clades. The virus was found only in the 4-month-old bear and not in other captive polar bears tested. We surmised, therefore, that the polar bear was infected from an unknown reservoir, illustrating that adenoviral diversity remains underestimated and that cross-species transmission of viruses can occur even under conditions of relative isolation.

IMPORTANCE Cross-species transmission of viral pathogens is becoming an increasing problem for captive-animal facilities. This study highlights how animals in captivity are vulnerable to novel opportunistic pathogens, many of which do not result in straightforward diagnosis from symptoms and histopathology. In this study, a novel pathogen was suspected to have contributed to the death of a juvenile polar bear. HTS techniques were employed, and a novel Mastadenovirus was isolated. The virus was present in both the tissue and blood samples. Phylogenetic analysis of the virus at both the gene and genome levels revealed that it is highly divergent to other known mastadenoviruses. Overall, this study shows that animals in isolated conditions still come into contact with novel pathogens, and for many of these pathogens, the host reservoir and mode of transmission are yet to be determined.

Adenoviral vectors coated with PAMAM dendrimer conjugates allow CAR independent virus uptake and targeting to the EGF receptor

Adenovirus type 5 (Ad) is an efficient gene vector with high gene transduction potential, but its efficiency depends on its native cell receptors coxsackie- and adenovirus receptor (CAR) for cell attachment and α(v)β(3/5) integrins for internalization. To enable transduction of CAR negative cancer cell lines, we have coated the negatively charged Ad by noncovalent charge interaction with cationic PAMAM (polyamidoamine) dendrimers. The specificity for tumor cell infection was increased by targeting the coated Ad to the epidermal growth factor receptor using the peptide ligand GE11, which was coupled to the PAMAM dendrimer via a 2 kDa PEG spacer. Particles were examined by measuring surface charge and size, the degree of coating was determined by transmission electron microscopy. The net positive charge of PAMAM coated Ad enhanced cellular binding and uptake leading to increased transduction efficiency, especially in low to medium CAR expressing cancer cell lines using enhanced green fluorescent protein or luciferase as transgene. While PAMAM coated Ad allowed for efficient internalization, coating with linear polyethylenimine induced excessive particle aggregation, elevated cellular toxicity and lowered transduction efficiency. PAMAM coating of Ad enabled successful transduction of cells in vitro even in the presence of neutralizing antibodies. Taken together, this study clearly proves noncovalent, charge-based coating of Ad vectors with ligand-equipped dendrimers as a viable strategy for efficient transduction of cells otherwise refractory to Ad infection.

Oncolytic adenovirus research and applications

Cancer treatments have improved steadily, but still only few metastatic solid tumors can be cured. Apoptosis-resistant clones frequently develop following standard treatments. Resistance factors are shared between different treatment regimens and, therefore, loss of response can occur rapidly, despite changing the drug, and there is a tendency for crossresistance between modalities. Therefore, new agents with novel mechanisms of action are desperately needed. Oncolytic adenoviruses, featuring cancer-selective cell lysis and spread, constitute an interesting drug platform aimed towards the goals of tumor specificity, and have been engineered in a variety of ways to improve their selectivity and efficacy. They allow rational drug development by the genetic incorporation of targeting mechanisms that can exert their function at different stages of the viral replication cycle. Owing to their immunogenicity, adenoviruses are particularly attractive for immunostimulatory purposes.

Role of RGD-containing ligands in targeting cellular integrins: Applications for ovarian cancer virotherapy (Review)

The purpose of this article was to review the current strategies of targeted therapy to integrins and define the best course of future research in ovarian cancer targeting. Cell surface integrin targeting has been used as a strategy for targeted therapy of several diseases with some success. The combination of virotherapy and integrin-targeting shows promise as a method for targeting ovarian cancer. More specifically, targeting of ovarian cancer with integrin-directed adenoviruses may lead to therapy with fewer toxicities and side effects. This article offers a review of the benefits of integrin-specific targeted therapy for several diseases and proposes a unique anti-ovarian cancer strategy involving the combination of the above with virotherapy as a potential anti-ovarian cancer treatment.

Novel cationic SLN containing a synthesized single-tailed lipid as a modifier for gene delivery

Cationic solid lipid nanoparticles (SLN) can bind DNA directly via ionic interaction and mediate in vitro gene transfection. However, toxicity is still an obstacle, which is strongly dependent on the cationic lipid used. In the present study, a novel single-tailed cationic lipid, 6-lauroxyhexyl lysinate (LHLN), was synthesized and used as a modifier to prepare stable SLN-DNA complexes by a nanoprecipitation method. The commonly used cationic lipid cetyltrimethylammonium bromide (CTAB) modified SLN-DNA formulation served as a contrast. These two formulations were characterized and compared in terms of morphology, particle size, surface charge, DNA binding capacity, release profile, cytotoxicity, and transfection efficiency. The LHLN SLN-DNA complexes had a similar spherical morphology, a relatively narrow particle size distribution and a more remarkable DNA loading capability compared to the CTAB ones. Most importantly, LHLN modified SLN had a higher gene transfection efficiency than the naked DNA and CTAB ones, which was approximately equal to that of Lipofectamine-DNA complexes, and a lower cytotoxicity compared with CTAB-SLN and Lipofectamine 2000. Thus, the novel cationic SLN can achieve efficient transfection of plasmid DNA, and to some extent reduce the cytotoxicity, which might overcome some drawbacks of the conventional cationic nanocarriers in vivo and may become a promising non-viral gene therapy vector.

Anionic solid lipid nanoparticles supported on protamine/DNA complexes

The objective of this study was to design novel anionic ternary nanoparticles for gene delivery. These ternary nanoparticles were equipped with protamine/DNA binary complexes (150-200 nm) as the support, and the anionic formation was achieved by absorption of anionic solid lipid nanoparticles (≤20 nm) onto the surface of the binary complexes. The small solid lipid nanoparticles (SLNs) were prepared by a modified film dispersion-ultrasonication method, and adsorption of the anionic SLNs onto the binary complexes was typically carried out in water via electrostatic interaction. The formulated ternary nanoparticles were found to be relatively uniform in size (257.7 ± 10.6 nm) with a 'bumpy' surface, and the surface charge inversion from 19.28 ± 1.14 mV to -17.16 ± 1.92 mV could be considered as evidence of the formation of the ternary nanoparticles. The fluorescence intensity measurements from three batches of the ternary nanoparticles gave a mean adsorption efficiency of 96.75 ± 1.13%. Circular dichroism spectra analysis showed that the protamine/DNA complexes had been coated by small SLNs, and that the anionic ternary nanoparticles formed did not disturb the construction of the binary complexes. SYBR Green I analysis suggested that the ternary nanoparticles could protect the DNA from nuclease degradation, and cell viability assay results showed that they exhibit lower cytotoxicity to A549 cells compared with the binary complexes and lipofectamine. The transfection efficiency of the ternary nanoparticles was better than that of naked DNA and the binary complexes, and almost equal to that of lipofectamine/DNA complexes, as revealed by inversion fluorescence microscope observation. These results indicated that the anionic ternary nanoparticles could facilitate gene transfer in cultured cells, and might alleviate the drawbacks of the conventional cationic vector/DNA complexes for gene delivery in vivo.

Antiadenoviral Effect of the α5β1 Integrin Receptor Ligand, GRGDSP Peptide, in Serotypes That Cause Acute Keratoconjunctivitis

BACKGROUND/AIMS

In adenoviral conjunctivitis, the infection process starts by the attachment of adenoviral fibers to conjunctival epithelial cells that contain the receptor for the adenovirus. The alpha 5 beta 1 integrin receptor ligand, GRGDSP peptide, contains the arginine-glycine-aspartate-binding motif which is common to the Coxsackie adenovirus receptor and integrins that are known to be adenoviral receptors. We evaluated the antiadenoviral effect of an expected adenoviral receptor inhibitor, GRGDSP peptide,in vitro.

METHODS

Adenovirus types 3, 4, 8, 19 and 37 were used. After calculating the 50% cytotoxic concentration of GRGDSP peptide, the adenovirus was cultivated with the agent for 7 days under serial dilution. Adenoviral DNA was qualitatively measured by real-time PCR.

RESULTS

GRGDSP peptide showed an inhibitory effect against adenoviral proliferation in all serotypes except type 4 in a dose-dependent manner.

CONCLUSION

This result suggests that the alpha 5 beta 1 integrin receptor ligand, GRGDSP peptide, has antiadenoviral activity in vitro, and the possibility of being used for local treatment of epidemic keratoconjunctivitis.

Viral dynamics in transplant patients: implications for disease

Viral infections cause substantial morbidity and mortality in transplant patients. Quantifying viral loads is widely appreciated as a direct means to diagnose and monitor the course of viral infections. Recent studies indicate that the kinetics of viral load changes rather than single viral load measurements better correlate with organ involvement. In this Review, we will summarise the current knowledge regarding the kinetics of viruses relevant to transplantation including cytomegalovirus, Epstein-Barr virus, the herpes viruses 6 and 7, hepatitis C virus, GB virus C, adenovirus, and the emerging human polyomavirus type BK. We discuss the implications of viral kinetics for organ pathology as well as for the evaluation of antiviral interventions in transplant patients.

Calcium-dependent viral internalization is required for adenovirus type 7 induction of IL-8 protein

The host response to adenovirus (Ad) infection involves induction of cytokines in lung epithelia. We have demonstrated induction of the lung neutrophil chemokine interleukin-8 (IL-8) by Ad7, a major lung pathogen, in A549 lung epithelial cells and lung tissue through activation of the Erk signaling pathway. However, the mechanism of IL-8 induction is still unclear. In this paper, we first showed that Ad7 viral gene expression is not essential for IL-8 induction as psoralen-UV inactivation of Ad7 did not affect IL-8 mRNA induction or IL-8 protein induction in A549 cells. We then inhibited internalization of Ad7 by treatment of A549 cells with EGTA in calcium-free medium during exposure to Ad7. We verified that this treatment inhibited Ad internalization by confocal microscopy, FACS analysis and Ad E1A and fiber mRNA expression. Preventing internalization by calcium depletion did not inhibit Erk activation by Ad7. However, calcium-dependent internalization was required for IL-8 protein production in Ad7 exposed cells. This is not likely due to an effect of calcium depletion on downstream Erk signaling or IL-8 protein production since calcium depletion did not block IL-8 protein production stimulated by PMA, and because addition of EGTA subsequent to Ad7 internalization also did not prevent Ad induction of IL-8. These studies indicate that Ad7 internalization is calcium-dependent and is required for IL-8 protein induction upon Ad7 infection. Ad7 induction of Erk is independent of calcium and does not require virus internalization.

Adenovirus-mediated p53 tumor suppressor gene therapy of osteosarcoma

The clinical outcome for osteosarcoma (OS) remains discouraging despite efforts to optimize treatment using conventional modalities including surgery, radiotherapy and chemotherapy. Novel therapeutic approaches based on our expanding understanding of the mechanisms of tumor cell killing have the potential to alter this situation. Tumor suppressor gene therapy aims to restore the function of a tumor suppressor gene lost or functionally inactivated in cancer cells. One such molecule, the p53 tumor suppressor gene plays a critical role in safeguarding the integrity of the genome and preventing tumorigenesis. Introduction of wild-type (wt) p53 into transformed cells has been shown to be lethal for most cancer cells in vitro, but clinical trials of p53 gene replacement have had limited success. Analysis of these clinical trials highlighted the insufficient efficacy of current vectors and low proapoptotic activity of wt p53 as a single agent in vivo. In this review, a contemporary summarization of the current status of adenovirus-mediated p53 gene therapy of OS is presented. Advancement in our understanding of p53 tumor suppressor activity, the molecular biology of chemoresistant OS, and recent advances in tumor targeting with adenoviral vectors are also addressed. Based on these parameters, prospects for future investigations are proposed.

Cross-species transfer of viruses: implications for the use of viral vectors in biomedical research, gene therapy and as live-virus vaccines

All living organisms are continuously exposed to a plethora of viruses. In general, viruses tend to be restricted to the natural host species which they infect. From time to time viruses cross the host-range barrier expanding their host range. However, in very rare cases cross-species transfer is followed by the establishment and persistence of a virus in the new host species, which may result in disease. Recent examples of viruses that have crossed the species barrier from animal reservoirs to humans are hantavirus, haemorrhagic fever viruses, arboviruses, Nipah and Hendra viruses, avian influenza virus (AI), monkeypox virus, and the SARS-associated coronavirus (SARS-CoV). The opportunities for cross-species transfer of mammalian viruses have increased in recent years due to increased contact between humans and animal reservoirs. However, it is difficult to predict when such events will take place since the viral adaptation that is needed to accomplish this is multifactorial and stochastic. Against this background the intensified use of viruses and their genetically modified variants as viral gene transfer vectors for biomedical research, experimental gene therapy and for live-vector vaccines is a cause for concern. This review addresses a number of potential risk factors and their implications for activities with viral vectors from the perspective of cross-species transfer of viruses in nature, with emphasis on the occurrence of host-range mutants resulting from either cell culture or tropism engineering. The issues are raised with the intention to assist in risk assessments for activities with vector viruses.

Adenovirus types 11p and 35 attach to and infect primary lymphocytes and monocytes, but hexon expression in T-cells requires prior activation

Hematopoietic cells are attractive targets for gene therapy, but the conventional adenovirus (Ad) vectors, based on Ad5, transduce these cells inefficiently. One reason for low permissiveness of hematopoietic cells to infection by species C Ads appears to be inefficient attachment. Vectors pseudotyped with species B fibers are clearly more efficient at transducing hematopoietic cells than Ad5. To evaluate which Ad species B type(s) would be the most efficient vector(s) for primary T-cells, B-cells and monocytes, attachment to and entry of the species B1 serotypes 3p and 7p and the species B2 serotypes 11p and 35 into primary PBMCs was studied. Ad11p and Ad35 were the only serotypes to show efficient binding and for which uptake by PBMCs could be detected. Infection of PBMCs by Ad5, Ad11p and Ad35 was compared. Expression of Ad hexons was detected in stimulated PBMCs, most frequently in T-cells, and in unstimulated monocytes, although B-cells appear to be refractory to productive infection. Replication of Ad DNA was severely restricted in most PBMCs. Neither hexon expression nor genome replication could be detected in unstimulated lymphocytes, but FISH and a real-time PCR-based assay suggested that Ad11p and Ad35 DNA reach the nucleus. Activation thus appears to be required for T-cells to be permissive to Ad gene expression. In summary, there are substantial differences between Ad3p and Ad7p on the one hand and Ad11p and Ad35 on the other, in their ability to interact with PBMCs. Ad11p and Ad35 probably represent vectors of choice for these cell types.

Crystal structure of enteric adenovirus serotype 41 short fiber head

Human enteric adenoviruses of species F contain two fibers in the same virion, a long fiber which binds to coxsackievirus and adenovirus receptor (CAR) and a short fiber of unknown function. We have determined the high-resolution crystal structure of the short fiber head of human adenovirus serotype 41 (Ad41). The short fiber head has the characteristic fold of other known fiber heads but has three unusual features. First, it has much shorter loops between the beta-strands. Second, one of the usually well-ordered beta-strands on the distal face of the fiber head is highly disordered and this same region is sensitive to digestion with pepsin, an enzyme occurring naturally in the intestinal tract, the physiological environment of Ad41. Third, the AB loop has a deletion giving it a distinct conformation incompatible with CAR binding.

Analysis of adenovirus gene transfer into adult neural stem cells

Adult neural stem cells (aNSCs) represent an attractive source for the production of specific types of neurons in degenerative CNS diseases and for the development of new regenerative gene therapies. However, the use of adult NSCs for transplantation and gene replacement strategies requires efficient gene expression in the cells. Due to the low pathogenicity of adenovirus (Ad) for humans, its large delivery capacity, and long-term transgene expression, Ad vectors are widely used. Here, we tested the potential of the Ad vector system to transduce adult NSCs. Analysis of Ad receptor expression in primary aNSCs revealed a complete lack of the coxsackie-adenovirus receptor and no or low expression of alphanu- and beta5-integrins, respectively, on mRNA and protein level. Consistently, transduction at different multiplicities of infection using an Ad vector expressing the enhanced green fluorescent protein (GFP) showed that adult NSCs are particularly resistant to Ad infection even at highest MOI (1000) in contrast to differentiated types of neural cells.

Retargeting of adenoviral vector using basic fibroblast growth factor ligand for malignant glioma gene therapy

Object. Adenovirus vector (AdV)—mediated gene delivery has been recently demonstrated in clinical trials as a novel potential treatment for malignant gliomas. Combined coxsackievirus B and adenovirus receptor (CAR) has been shown to function as an attachment receptor for multiple adenovirus serotypes, whereas the vitronectin integrins (αvβ3 and αvβ5) are involved in AdV internalization. In resected glioma specimens, the authors demonstrated that malignant gliomas have varying levels of CAR, αvβ3, and αvβ5 expression.

Methods. A correlation between CAR expression and the transduction efficiency of AdV carrying the green fluorescent protein in various human glioblastoma multiforme (GBM) cell lines and GBM primary cell lines was observed. To increase transgene activity in in vitro glioma cells with low or deficient levels of CAR, the authors used basic fibroblast growth factor (FGF2) as a targeting ligand to redirect adenoviral infection through its cognate receptor, FGF receptor 1 (FGFR1), which was expressed at high levels by all glioma cells. These findings were confirmed by in vivo study data demonstrating enhanced transduction efficiency of FGF2-retargeted AdV in CAR-negative intracranial gliomas compared with AdV alone, without evidence of increased angiogenesis.

Conclusions. Altogether, the results demonstrated that AdV-mediated gene transfer using the FGF2/FGFR system is effective in gliomas with low or deficient levels of CAR and suggested that FGF2-retargeting of AdV may be a promising approach in glioma gene therapy.

Targeting Viral-Mediated Transduction to the Lung Airway Epithelium with the Anti-inflammatory Cationic Lipid Dexamethasone–Spermine

We formulated adenovirus (AdV) vectors with cationic steroid liposomes containing dexamethasone-spermine (DS)/dioleoylphosphatidylethanolamine (DOPE) in an effort to overcome the lack of apically expressed AdV vector receptors on airway epithelial cells and to reduce the inflammation associated with AdV vector exposure. An AdV vector (1 to 2.5 x 10(11) genome copies) expressing human placental alkaline phosphatase or beta-galactosidase (LacZ) was delivered alone or complexed with DS/DOPE, DC-Chol/DOPE, or dexamethasone to C57Bl/6 mice via intranasal instillation. Formulation of the AdV vector with DS/DOPE and DC-Chol/DOPE resulted in transgene expression targeted only to the airway epithelial cells with minimal expression in alveolar cells, while AdV alone caused high alveolar transduction. The DS/DOPE and dexamethasone formulations greatly reduced cellular infiltrates compared to AdV vector alone, while formulation with DC-Chol/DOPE did not. IFN-gamma was significantly elevated at day 7 in mice receiving only the AdV vector compared to the AdV vector formulated with DS/DOPE, DC-Chol/DOPE, or dexamethasone. Lipid formulation of adeno-associated virus vector expressing LacZ also produced airway epithelial targeting, similar to the AdV vector. Viral vectors can be formulated with DS/DOPE to improve targeting to the airway epithelium in vivo and to attenuate vector-induced inflammation through the pharmacological activity of DS.

Discovery of targeting peptides for selective therapy of medullary thyroid carcinoma

BACKGROUND

Adenovirus efficiently infects a broad range of target cells, thereby preventing selective gene transfer. Moreover, several cell types and tissues including primary tumors are refractory to adenoviral infection, mainly because of low expression levels of coxsackie-adenovirus receptor (CAR). Thus, identification of cancer-selective ligands which yield gene transfer to neoplastic cells by minimizing transduction of normal cells is a key issue for successful cancer therapy.

METHODS

We initially analyzed adenoviral receptor expression in human medullary thyroid carcinoma (MTC) cells. MTC cell-specific peptides were isolated by biopanning a phage display peptide library on cultured cancer cells and on tumors in vivo and further characterized.

RESULTS

We found significant differences in CAR and alphav-integrin protein levels between MTC-derived TT cells in vitro and established xenograft tumors in mice, indicating a lack of alphav-integrin expression on growing tumors. MTC-specific candidates were identified by performing three rounds of subtraction. Selected phages showed up to 22-fold higher binding efficiency for TT cells when compared with wild-type M13 phage or other human cell lines and tumor tissue in vivo. Homing to TT cells of the best binding phage was clearly blocked in the presence of specific peptide, whereas no phage competition was observed with an unspecific peptide. The best binding peptide mediated efficient internalization of the phage. Importantly, specific binding and internalization was also mediated by the identified peptide within the adenoviral context.

CONCLUSIONS

Our results indicate that the identified ligand should be suitable to improve selectivity of adenoviral gene transfer to medullary thyroid tumors in vivo.

In vitro efficacy of Fas ligand gene therapy for the treatment of bladder cancer

Previous investigations have revealed that bladder cancer cells are generally resistant to Fas-mediated apoptosis by conventional Fas agonists. However, the ability of these cell lines to undergo Fas-mediated apoptosis may have been underappreciated. As a result, we investigated the in vitro efficacy of Fas ligand gene therapy for bladder cancer. Three human bladder cancer lines (T24, J82, and 5637) were treated with the conventional Fas agonist CH-11, a monoclonal antibody to the Fas receptor. Cells were also treated with a replication-deficient adenovirus containing a modified murine Fas ligand gene fused to green fluorescent protein (GFP), AdGFPFasL. A virus containing the GFP gene alone was used to control for viral toxicity (AdGFP). Cell death was quantified using a tetrazolium-based (MTS) assay. Cells were also evaluated by Western blotting to evaluate poly (ADP-ribose) polymerase, caspase 8, and caspase 9 cleavage and by flow cytometry to determine the presence of coxsackie/adenovirus receptor (CAR). These studies confirmed bladder cancer resistance to cell death by the anti-Fas monoclonal antibody CH-11. This resistance was overcome with AdGFPFasL at a multiplicity of infection (MOI) of 1000 achieving over 80% cell death in all cell lines. Furthermore, greater than 80% cell death was evident in 5637 cells treated with low-dose AdGFPFasL (MOI=10). 5637 cells expressed significantly higher levels of surface CAR than J82 or T24 cells (P<.05). AdGFPFasL is cytotoxic to bladder cancer cells that would otherwise be considered Fas resistant, supporting its in vivo potential. Enhanced sensitivity to AdGFPFasL may be in part due to increased cell surface CAR levels.

Human hematopoietic (CD34+) stem cells possess high-affinity receptors for adenovirus type 11p

Gene transfer into human hematopoietic stem cells using Ad5 is inefficient due to lack of the primary receptor CAR and the secondary receptors alphavbeta3 integrin and alphavbeta5 integrin, and due to the high seroprevalence of Ad5 antibodies in most adults, resulting in diminished gene transduction. In the present study, we screened six species (species A-F) of adenovirus, displaying different tropisms for interaction with CD34+ cells, at the level of virus attachment and expression. Virus particles were biotinylated and their binding capacity was determined by FACS analysis using streptavidin-FITC. Ad11p, Ad35, and Ad3 (species B) showed high binding affinity, while Ad7, Ad11a (species B), and Ad37 (species D) displayed intermediate affinity. Virions of Ad4 (species E), Ad5 (species C), Ad31 (species A), and Ad41 (species F) hardly bound to hematopoietic progenitor cells. Using a double-labeling system, we demonstrated that adenoviruses bind to quiescent CD34+ cells. Ad11p virions showed the highest affinity among the adenoviruses detected. We further confirmed that virus fiber-specific receptors were present on the hematopoietic progenitor cell surface, because both recombinant fiber of Ad11p and specific antiserum against rfiber could block virus attachment. The ability of the adenoviruses to infect hematopoietic cells was studied by immunofluorescence staining. The adenoviruses from species B and Ad37 showed higher infectivity than Ad31, Ad5, Ad4, and Ad41. Among the studied species B adenoviruses, Ad11p manifested a superior infectivity. Thus, we have confirmed that these cells have high-affinity receptors for species B:2 human adenovirus, Ad11p, and this virus may be used as candidate vector to target therapeutic genes to hematopoietic stem cells.

Biodistribution of radioiodinated adenovirus fiber protein knob domain after intravenous injection in mice

The knob domains from the fiber proteins of adenovirus serotypes 2 and 12 were labeled with radioiodine and then injected into the bloodstreams of mice. Knob proteins with functional binding sites for the coxsackie and adenovirus receptor (CAR) were cleared rapidly from the circulation, with radioactivity appearing predominantly in the stomach, while knob mutants unable to bind to CAR remained in the blood circulation for a prolonged period. The clearance of radiolabeled wild-type knob from the blood was slowed by coinjecting an excess of unlabeled wild-type knob protein. An earlier study showed that (99m)Tc-labeled knob protein with intact CAR-binding activity also cleared rapidly from the blood circulation of mice, with radioactivity accumulating predominantly in the liver (K. R. Zinn et al., Gene Ther. 5:798-808, 1998). Together these results suggest that rapid clearance of knob protein from the blood results from specific binding to CAR in the liver and that the bound knob then enters a degradative pathway. The elevated levels of radioiodine in the stomach observed in our experiments are consistent with deiodination of labeled knob by dehalogenases in hepatocyte microsomes and uptake of the resultant free radioiodine by Na/I symporters in the gastric mucosa. Although CAR has been shown to localize in tight junctions of polarized epithelial cells, where it functions in intercellular adhesion, the results of our study suggest that a subset of CAR molecules in the liver is highly accessible to ligands in the blood and able to rapidly deliver bound ligand to an intracellular degradative compartment.

Combination with CD/5-FC gene therapy enhances killing of human bladder-cancer cells by radiation

BACKGROUND

Resistance to radiation and chemotherapy is a significant obstacle to the treatment of advanced bladder cancer. Gene therapy combined with radiation represents a new approach to cancer treatment. In the present study, we investigated whether adenovirally directed, cytosine deaminase (CD)/5-fluorocytosine (5-FC) gene therapy could induce cell toxicity and radiosensitization through the intracellular production of 5-fluorouracil (5-FU) in bladder-cancer cells.

METHODS

Three human bladder-cancer cell lines, KK47 (wild-type p53+), T24 (p53 mutated) and 5637 (p53 mutated), were investigated. A recombinant adenovirus vector containing the CD gene (Ad-RSV-CD) was used. Cells were infected with Ad-RSV-CD and treated with 5-FC. Forty-eight hours after infection, the cells were irradiated and cytotoxicity assays performed to determine the extent of increase in in vitro cytotoxicity. A KK47 subcutaneous tumor-xenografts model was used in an animal study to examine the tumor growth inhibitory effect of this combination therapy. Ad-RSV-CD was directly injected into the tumor and daily 5-FC was intraperitoneally injected. Forty-eight hours after injection of Ad-RSV-CD, the tumor was irradiated. The tumor volume was measured every day.

RESULTS

In all three cell lines, the combination treatment enhanced the cell killing of human bladder-cancer cells in vitro. It also enhanced the tumor-growth inhibition in the KK47 tumor model.

CONCLUSIONS

In the present study, we demonstrated that CD/5-FC gene therapy combined with radiation therapy enhances cell killing of human bladder-cancer cells in in vitro and in vivo animal models.

Adenovirus interaction with its cellular receptor CAR

Representative adenoviruses from four of the five major virus subgroups have been shown to interact with the 46-kDa coxsackievirus and adenovirus receptor (CAR) that is widely expressed on many human cell types, suggesting that the ability to bind CAR may be a conserved feature of many of the approximately 50 known adenovirus serotypes. Receptor binding is a function of the distal 'knob' domain of the trimeric viral fiber protein. Here we review recent structural characterizations of knob, CAR and knob-CAR complexes, and we discuss how knob architecture may have evolved to accommodate opposing selective pressures to vary antigenic structure while conserving receptor binding specificity. In contrast to the hypervariability of the solvent-exposed surface of knob, the CAR receptor was found to be non-polymorphic.

Expression of the coxsackievirus and adenovirus receptor in musculoskeletal tumors and mesenchymal tissues: efficacy of adenoviral gene therapy for osteosarcoma

Recombinant adenovirus is used as a competent vector in a wide spectrum of cancer gene therapies. Adenovirus infection depends on coxsackievirus and adenovirus receptor (CAR)-mediated virus attachment to the cell surface. However, the expression levels of CAR and the efficiency of adenoviral gene transduction in musculoskeletal tumors have not been systematically investigated. To study the feasibility of gene therapy in musculoskeletal tumors, the expression levels of CAR and the antiproliferative effect of an adenovirally transduced wild-type p53 tumor suppressor gene were examined in 15 distinct musculoskeletal tumor cell lines, 19 tumor tissue samples, and the corresponding pathologically unremarkable mesenchymal tissues. The expression levels of the CAR gene were significantly higher in six of seven osteosarcoma cell lines and two of five osteosarcoma tissue samples than in the other cell lines, musculoskeletal tumors, and mesenchymal tissues. CAR expression levels were closely correlated with adenoviral gene transduction efficiency and the antiproliferative effect of a transduced adenoviral p53 gene in the tested cell lines. In addition, an immunocytochemical study confirmed that transfected green fluorescent protein (GFP) borne by Ad-CAG-GFP was expressed at the cell surface of CAR-positive cells. These results indicate that CAR expression is a critical determinant of transduction efficiency in adenovirus-based gene therapy. Most osteosarcomas appeared to express high levels of CAR, and thus adenovirus-mediated p53 gene therapy is likely to be suitable for the treatment of such tumors.

Modulation of adenovirus vector tropism via incorporation of polypeptide ligands into the fiber protein

The efficacy of adenovirus (Ad)-based gene therapy might be significantly improved if viral vectors capable of tissue-specific gene delivery could be developed. Previous attempts to genetically modify the tropism of Ad vectors have been only partially successful, largely due to the limited repertoire of ligands that can be incorporated into the Ad capsid. Early studies identified stringent size limitations imposed by the structure of the Ad fiber protein on ligands incorporated into its carboxy terminus and thus limited the range of potential ligand candidates to short peptides. We have previously identified the HI loop of the fiber knob domain as a preferred site for the incorporation of targeting ligands and hypothesized that the structural properties of this loop would allow for the insertion of a wide variety of ligands, including large polypeptide molecules. In the present study we have tested this hypothesis by deriving a family of Ad vectors whose fibers contain polypeptide inserts of incrementally increasing lengths. By assessing the levels of productivity and infectivity and the receptor specificities of the resultant viruses, we show that polypeptide sequences exceeding by 50% the size of the knob domain can be incorporated into the fiber with only marginal negative consequences on these key properties of the vectors. Our study has also revealed a negative correlation between the size of the ligand used for vector modification and the infectivity and yield of the resultant virus, thereby predicting the limits beyond which further enlargement of the fiber knob would not be compatible with the virion's integrity.

Targeted adenoviral vectors

Replication-defective vectors based on human adenovirus serotypes 2 and 5 (Ad2 and Ad5) possess a number of attributes which favor their use as gene delivery vehicles in gene therapy applications. However, the widespread distribution of the primary cellular receptor for Ad, the coxsackievirus and adenovirus receptor (CAR), allows Ad vectors to infect a broad range of cells in the host. Conversely, a number of tissues which represent important targets for gene therapy, such as the airway epithelium and cancer cells, are refractory to Ad infection due a paucity of CAR. Thus, there is a strong rationale for the development of CAR-independent Ad vectors capable of enhanced specificity and efficiency of gene transfer to target cells. In this article we review the approaches which have been employed to generate tropism-modified Ad vectors. These targeting strategies have led to improvements in the safety and efficacy of Ad vectors and have the potential to yield an increased therapeutic benefit in the human clinical context.

Human adenoviruses of subgenera B, C, and E with various tropisms differ in both binding to and replication in the epithelial A549 and 293 cells

Adenoviruses of six subgenera, namely, adenovirus 31 (Ad31) (subgenus A), Ad3, Ad7, Ad11p, Ad11a, and Ad35 (subgenus B), Ad5v and Ad5p (subgenus C), Ad37 (subgenus D), Ad4 (subgenus E), and Ad41 (subgenus F), were studied. The relative binding properties of different adenoviruses to 293 (human kidney embryonic cells) and A549 (human lung carcinoma cells) cells were compared by flow cytometry. All analyzed adenoviruses bound to cells in a dose-dependent manner. The binding capacity showed that Ad11p, Ad35 (subgenus B:2) with kidney tropism, and Ad4 (subgenus E), which can cause adenopharyngoconjunctivitis, bound strongly to both A549 and 293 cells. The other members of subgenus B and Ad37 of subgenus D manifested an intermediate binding capacity. The analyzed adenoviruses of subgenera A, C, and F manifested a low affinity. Adenoviruses of subgenera B:2 and E manifested high binding affinity to preparations of cell membranes from the epithelial cell lines. Reciprocal competition experiments using Ad11p and Ad4 demonstrated that the two viruses did not block each other. Antibodies against alphavbeta3 and alphavbeta5 reduced the binding of Ad5v virions and slightly impaired the binding of Ad4 but did not affect Ad11p binding to the A549 cell surface. Recombinant fiber proteins of Ad11p and Ad35 reciprocally blocked the binding of both viruses to the epithelial cells but they could not block Ad4. The hexon protein expression of Ad11p and Ad4 was 100 times more efficient than that of the Ad5 vector (pFG140), whereas the infectivity of Ad11p and Ad4 was 40- to 200-fold that of the commonly used Ad5v vector. Taken together, our findings demonstrate that Ad11p and Ad4 bind different receptor molecules and that the fibers of these two viruses provide the predominant high degree of binding, which obviously is a requirement for subsequent internalization and efficacious expression.

Drug-resistant human bladder-cancer cells are more sensitive to adenovirus-mediated wild-type p53 gene therapy compared to drug-sensitive cells

We investigated the therapeutic potential and molecular mechanism of adenovirus-mediated wt p53 gene therapy for drug-resistant human bladder cancers. KK47, a human bladder-cancer cell line, along with the drug-resistant sublines KK47/DDP10, KK47/DDP20 (cisplatin-resistant) and KK47/ADM (doxorubicin-resistant) were used for the experiments. All 4 KK47 cell lines had genetically normal p53 genes. Using an in vitro cytotoxicity assay, the drug-resistant cell lines were more sensitive to Ad-CMV-p53 cell killing than the KK47 parental cell line. Ad-CMV-p53 induced higher levels of p53 protein and mRNA in the drug-resistant cell lines than in the parental cell line and, consequently, higher levels of p21 and Bax mRNA, which resulted in higher percentages of G(1) cell-cycle arrest and apoptosis. The higher efficiencies of adenoviral gene transfer in the drug-resistant cell lines were confirmed by X-gal staining after infection with Ad-CMV-beta-gal. In conclusion, adenovirus-mediated wt p53 gene therapy was more effective in the drug-resistant bladder-cancer cell lines than in the drug-sensitive bladder-cancer cell line.

Muscle-specific overexpression of the adenovirus primary receptor CAR overcomes low efficiency of gene transfer to mature skeletal muscle

Significant levels of adenovirus (Ad)-mediated gene transfer occur only in immature muscle or in regenerating muscle, indicating that a developmentally regulated event plays a major role in limiting transgene expression in mature skeletal muscle. We have previously shown that in developing mouse muscle, expression of the primary Ad receptor CAR is severely downregulated during muscle maturation. To evaluate how global expression of CAR throughout muscle affects Ad vector (AdV)-mediated gene transfer into mature skeletal muscle, we produced transgenic mice that express the CAR cDNA under the control of the muscle-specific creatine kinase promoter. Five-month-old transgenic mice were compared to their nontransgenic littermates for their susceptibility to AdV transduction. In CAR transgenics that had been injected in the tibialis anterior muscle with AdVCMVlacZ, increased gene transfer was demonstrated by the increase in the number of transduced muscle fibers (433 +/- 121 in transgenic mice versus 8 +/- 4 in nontransgenic littermates) as well as the 25-fold increase in overall beta-galactosidase activity. Even when the reporter gene was driven by a more efficient promoter (the cytomegalovirus enhancer-chicken beta-actin gene promoter), differential transducibility was still evident (893 +/- 149 versus 153 +/- 30 fibers; P < 0.001). Furthermore, a fivefold decrease in the titer of injected AdV still resulted in significant transduction of muscle (253 +/- 130 versus 14 +/- 4 fibers). The dramatic enhancement in AdV-mediated gene transfer to mature skeletal muscle that is observed in the CAR transgenics indicates that prior modulation of the level of CAR expression can overcome the poor AdV transducibility of mature skeletal muscle and significant transduction can be obtained at low titers of AdV.

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.

Adenovirus type 7 penton purification of soluble pentamers from Escherichia coli and development of an integrin-dependent gene delivery system

Adenoviral gene therapy vectors suffer from the disadvantages of toxicity and immunogenicity associated with the expression of adenoviral genes from the vector backbone. We report here an alternative strategy for gene delivery that utilizes a single component of the adenoviral type 7 capsid, the penton base (Ad7PB). The Ad7PB gene was sequenced and its amino-acid composition was deduced from its nucleotide sequence. The penton was expressed in Escherichia coli as a soluble C-terminal fusion with glutathione S-transferase (GST-Ad7PB) and was purified by single-step affinity chromatography. Both GST-Ad7PB and cleaved (GST-free) Ad7PB retained the ability to fold into pentamers as observed by electron microscopy. GST-Ad7PB was able to bind a synthetic peptide (FK20) derived from the Ad type 7 fiber and retard DNA through a polylysine chain present at the C-terminus of this linker peptide. GST-Ad7PB was an effective cell transfecting agent when assayed on 293 cells. Transfection was not dependent upon the presence of lysosomotropic agents indicating efficient endosome escape capability. Excess of an RGD-containing peptide derived from Ad7PB was able to inhibit transfection indicating specific integrin-mediated uptake of the GST-Ad7PB-FK20-DNA complexes. We propose that Ad7 pentons can be developed into integrin-specific gene delivery agents.

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.

Maturation and lineage-specific expression of the coxsackie and adenovirus receptor in hematopoietic cells

Adenovirus vectors have been used to transfer genes into both hematopoietic progenitor cells and tumor cells, including carcinoma cells that have metastasized to bone marrow (BM). However, the relative susceptibility of different subsets of hematopoietic cells is unknown. In permissive cells adenoviral-mediated gene transfer is mediated by the coxsackievirus and adenovirus receptor (CAR) protein and alpha(v) integrins expressed on the cell surface of the target cells. This prompted us to investigate the expression of CAR on subpopulations of hematopoietic cells, determine whether this protein played a role in adenovirus-mediated gene transfer of hematopoietic cells and whether we could modulate CAR to enhance gene transfer efficiency. In this report we show that CAR is expressed on approximately 40% of all human BM cells, including erythroid and myeloid cells, but not lymphoid cells. Of the CD34(+) cells, 10%-15% expressed CAR, but this did not include most colony-forming progenitor cells, nor the most primitive CD38(-) subpopulation. The presence of CAR correlated well with gene transfer efficiency, but we were unable to induce CAR expression on immature, noncommitted progenitor cells. In conclusion, our results show that primitive hematopoietic progenitor cells lack CAR expression, but that expression is acquired during erythroid and myeloid differentiation.

Adenovirus type 41 lacks an RGD alpha(v)-integrin binding motif on the penton base and undergoes delayed uptake in A549 cells

Human adenovirus (Ad) types 2, 3 and 12 are known to interact with cell surface integrins alpha(v)beta(3) and alpha(v)beta(5) through an RGD motif carried by the penton base. This interaction is thought to augment virus entry after initial contact between the fiber and specific receptor(s). Ad40 and Ad41 are the only members of the human subgroup F adenoviruses. The penton base protein sequence of one Ad40 strain is known to carry the motif RGAD rather than RGD, suggesting that not all human adenoviruses use the above integrins for cell entry. We confirmed that different genomic variants of Ad40 all carry an RGAD motif on the penton base, and found that the Ad41 prototype and several other genomic variants of Ad41 carry the motif IGDD in place of RGAD or RGD. This region is most likely exposed on the Ad41 particle, but attempts to block Ad41 infectivity using a homologous peptide were unsuccessful. Infectivity of an Ad41 preparation as measured by fluorescent focus assay in A549 cells was highly dependent on the length of the adsorption period, indicating that fiber-mediated attachment is inefficient in these cells. Moreover, Ad41 virions adsorbed for 1 h were internalized in a semi-linear fashion over 8 h. This inefficient uptake may be a direct consequence of independence of subgroup F adenoviruses from alpha(v)beta(3) and alpha(v)beta(5) integrin-mediated endocytosis. Ad40 and Ad41 may thus have lost or may never have developed a dependence on the penton base RGD motif for entry.

Retargeted delivery of adenoviral vectors through fibroblast growth factor receptors involves unique cellular pathways

A major goal of gene therapy is to improve target specificity by delivering vectors through alternative cellular receptors. We previously reported that adenoviral vector delivery through basic fibroblast growth factor (FGF2) receptors enhances both cellular transduction and in vivo efficacy. We now present studies addressing the cellular pathways and mechanisms underlying these events. Cellular receptors for adenoviruses are not required for transduction by FGF2-retargeted vectors. Moreover, alpha(V) integrins can antagonize FGF2 retargeting, in contrast to their obligatory role in non-retargeted vector delivery. By contrast, high-affinity FGF receptors, which are overexpressed on potential tumor targets, are required for FGF2-retargeted transduction. Low-affinity heparan sulfate proteoglycan interactions, however, are not a prerequisite, in marked contrast to their obligatory role in FGF2 mitogenic signaling. By comparing receptor expression and ligand binding with transgene expression, we also demonstrate that FGF2 retargeting enhances transduction by mechanisms other than increasing the number of targeted cells. Rather, the use of alternative targeting ligands supports the conclusion that specific receptor interactions and intracellular events serve to enhance transgene expression. Together, these studies highlight the unique delivery and transduction pathways used by FGF2-retargeted adenoviruses, and help define the basis for their enhanced in vivo efficacy.

Receptors mediating adenovirus attachment and internalization

Adenovirus infection requires that the virus attach to cells and be internalized. Interaction between the viral fiber protein and specific cell surface receptors, such as the 46-kDa coxsackievirus and adenovirus receptor (CAR), is responsible for attachment; a second interaction between the viral penton base and cell surface integrins facilitates virus internalization. Expression of receptors may determine whether tissues are susceptible to adenovirus infection and adenovirus-mediated gene delivery.

CAR-dependent and CAR-independent pathways of adenovirus vector-mediated gene transfer and expression in human fibroblasts

Primary fibroblasts are not efficiently transduced by subgroup C adenovirus (Ad) vectors because they express low levels of the high-affinity Coxsackie virus and adenovirus receptor (CAR). In the present study, we have used primary human dermal fibroblasts as a model to explore strategies by which Ad vectors can be designed to enter cells deficient in CAR. Using an Ad vector expressing the human CAR cDNA (AdCAR) at high multiplicity of infection, primary fibroblasts were converted from being CAR deficient to CAR sufficient. Efficiency of subsequent gene transfer by standard Ad5-based vectors and Ad5-based vectors with alterations in penton and fiber was evaluated. Marked enhancement of binding and transgene expression by standard Ad5 vectors was achieved in CAR-sufficient fibroblasts. Expression by AdDeltaRGDbetagal, an Ad5-based vector lacking the arginine-glycine-aspartate (RGD) alphaV integrin recognition site from its penton base, was achieved in CAR-sufficient, but not CAR-deficient, cells. Fiber-altered Ad5-based vectors, including (a) AdF(pK7)betagal (bearing seven lysines on the end of fiber) (b) AdF(RGD)betagal (bearing a high-affinity RGD sequence on the end of fiber), and (c) AdF9sK betagal (bearing a short fiber and Ad9 knob), demonstrated enhanced gene transfer in CAR-deficient fibroblasts, with no further enhancement in CAR-sufficient fibroblasts. Together, these observations demonstrate that CAR deficiency on Ad targets can be circumvented either by supplying CAR or by modifying the Ad fiber to bind to other cell-surface receptors.

Coxsackievirus and adenovirus receptor amino-terminal immunoglobulin V-related domain binds adenovirus type 2 and fiber knob from adenovirus type 12

The extracellular region of the coxsackievirus and adenovirus receptor (CAR) is predicted to consist of two immunoglobulin (Ig)-related structural domains. We expressed the isolated CAR amino-terminal domain (D1) and a CAR fragment containing both extracellular Ig domains (D1/D2) in Escherichia coli. Both D1 and D1/D2 formed complexes in vitro with the recombinant knob domain of adenovirus type 12 (Ad12) fiber, and D1 inhibited adenovirus type 2 (Ad2) infection of HeLa cells. These results indicate that the adenovirus-binding activity of CAR is localized in the amino-terminal IgV-related domain and confirm our earlier observation that Ad2 and Ad12 bind to the same cellular receptor. Preliminary crystallization studies suggest that complexes of Ad12 knob bound to D1 will be suitable for structure determination.

Persistent infection promotes cross-species transmissibility of mouse hepatitis virus

Persistent infection with mouse hepatitis virus (MHV) strain A59 in murine DBT (delayed brain tumor) cells resulted in the emergence of host range variants, designated V51A and V51B, at 210 days postinfection. These host range mutants replicated efficiently in normally nonpermissive Chinese hamster ovary (CHO), in human hepatocarcinoma (HepG2), and to a lesser extent in human breast carcinoma (MCF7) cell lines. Little if any replication was noted in baby hamster kidney (BHK), green African monkey kidney (COS-7), feline kidney (CRFK), and swine testicular (ST) cell lines. By fluorescent antibody (FA) staining, persistent viruses V10B and V30B, isolated at days 38 and 119 days postinfection, also demonstrated very low levels of replication in human HepG2 cells. These data suggest that persistence may rapidly select for host range expansion of animal viruses. Pretreatment of HepG2 cells with a polyclonal antibody directed against human carcinoembryonic antigens (CEA) or with some monoclonal antibodies (Col-1, Col-4, Col-12, and Col-14) that bind human CEA significantly inhibited V51B infection. Under identical conditions, little or no blockade was evident with other monoclonal antibodies (kat4c or Col-6) which also bind the human CEA glycoproteins. In addition, an antibody (EDDA) directed against irrelevant antigens did not block V51B replication. Pretreatment with the Col-4 and Col-14 antibodies did not block Sindbis virus replication in HepG2 cells or MHV infection in DBT cells, suggesting that one or more CEA glycoproteins likely functioned as receptors for V51B entry into human cell lines. To test this hypothesis, the human biliary glycoprotein (Bgp) and CEA genes were cloned and expressed in normally nonpermissive BHK cell lines by using noncytopathic Sindbis virus replicons (pSinRep19). By growth curves and FA staining, human CEA and to a much lesser extent human Bgp functioned as receptors for V51B entry. Furthermore, V51B replication was blocked with polyclonal antiserum directed against human CEA and Bgp. Under identical conditions, the parental MHV strain A59 failed to replicate in BHK cells expressing human Bgp or CEA. These data suggest that MHV persistence may promote virus cross-species transmissibility by selecting for virus variants that recognize phylogenetic homologues of the normal receptor.

Altered tropism of an ovine adenovirus carrying the fiber protein cell binding domain of human adenovirus type 5

Ovine adenovirus OAV287 (OAV) is phylogenetically and serotypically distinct from human Ad5. OAV grows productively in CSL503 foetal ovine lung cells and abortively infects several human cell lines. OAV has a unique fiber and a penton protein that lacks a recognisable integrin-binding motif. It is not known whether a secondary receptor is required for infection. A hybrid virus was constructed in which the cell binding domain on the OAV fiber protein was exchanged for the equivalent region from human adenovirus type 5. The hybrid OAV grew to titres that were 1 to 2 log10 lower than wild-type OAV in permissive ovine cells. Human Ad5 also infected CSL503 cells but failed to compete with OAV for receptor binding sites on those cells. However, the hybrid virus did compete with Ad5, consistent with its use of the Ad primary receptor. The hybrid virus was also neutralised by Ad5 antiserum whereas OAV was not. Human 293 kidney and LNCaP prostate cell lines that were not detectably infected by OAV were infected by the hybrid virus and other human prostate and breast cancer cell lines showed greatly enhanced infectivity. Thus, modification of the fiber cell binding domain was sufficient to profoundly alter the tropism of OAV, suggesting that the interaction between the primary receptor and the virus particle is the major factor controlling virus entry during infection.

Limited entry of adenovirus vectors into well-differentiated airway epithelium is responsible for inefficient gene transfer

Investigations of the efficiency and safety of human adenovirus vector (AdV)-mediated gene transfer in the airways of patients with cystic fibrosis (CF) in vivo have demonstrated little success in correcting the CF bioelectrical functional defect, reflecting the inefficiency of AdV-mediated gene transfer to the epithelial cells that line the airway luminal surface. In this study, we demonstrate that low AdV-mediated gene transfer efficiency to well-differentiated (WD) cultured airway epithelial cells is due to three distinct steps in the apical membrane of the airway epithelial cells: (i) the absence of specific adenovirus fiber-knob protein attachment receptors; (ii) the absence of alphavbeta3/5 integrins, reported to partially mediate the internalization of AdV into the cell cytoplasm; and (iii) the low rate of apical plasma membrane uptake pathways of WD airway epithelial cells. Attempts to increase gene transfer efficiency by increasing nonspecific attachment of AdV were unsuccessful, reflecting the inability of the attached vector to enter (penetrate) WD cells via nonspecific entry paths. Strategies to improve the efficiency of AdV for the treatment of CF lung disease will require methods to increase the attachment of AdV to and promote its internalization into the WD respiratory epithelium.

Two closely related adenovirus genome types with kidney or respiratory tract tropism differ in their binding to epithelial cells of various origins

The host cell interactions of the genome types Ad11p and Ad11a of human adenovirus serotype 11, displaying kidney or respiratory tropism, were compared using FACS analysis. Kinetic experiments indicated that the virus binding stated immediately and reached a plateau after 30 min. The binding of biotinylated virions to seven continuous cell lines. A549, A498, J82, HeLa, CHO, MDCK, and human diploid fibroblasts (HEDF), was quantitated by FACS analysis. The binding capacities of the two viruses to all human cell lines but A549 cells appeared to differ. Ad11p virions manifested high affinities, whereas Ad11a virions presented low affinities. Neither of the two viruses bound to CHO or MDCK cells. Reciprocal competition experiments showed that the Ad11a virions could be weakly blocked by the Ad11p virions, whereas the Ad11p virions could not be competed at all by the Ad11a virions. The binding of the Ad11p virions to cells could be blocked by the rfiber antiserum of Ad11p, but not by the corresponding antiserum against Ad11a or Ad35p. A comparison of the cytopathogenicity of the seven cell lines infected by Ad11p and Ad11a demonstrated that the efficiency of the initial event of an adenovirus infection directly affects the outcome of the viral infection. The Ad11a in the A498, J82, HeLa, or HEDF cells that presented lower affinity and receptor concentration showed 100 times less infectivity than that in A549 cells displaying high affinity and receptor concentration. These results indicate that the cell susceptibility to Ad11p and Ad11a infection strongly depends on both the number of fiber receptors on the host cells and the receptor affinity for ligands on the fiber knob. Our findings also suggest that the receptors for Ad11p and Ad11a on the surface of different cell types may be different or on different sites.

Gene expression by atypical recombinant ovine adenovirus vectors during abortive infection of human and animal cells in vitro

An bovine adenovirus, which is phylogenetically distinct from the Mastadeno- and Aviadenoviruses, was used to construct recombinants in which reporter genes were expressed from the OAV major late, or human cytomegalovirus promoters. It was demonstrated by transgene expression that OAV could infect bovine nasal turbinate and rabbit kidney cells as well as a range of human cell types, including lung and foreskin fibroblasts as well as liver, prostate, breast, colon, and retinal lines. Some human lines, e.g., 293 and LNCaP were not detectably infected. Infection occurred even though OAV has a fiber protein with a unique cell binding domain and a penton protein that lacks the integrin-binding Arg-Gly-Asp motif which facilitates entry by human adenoviruses. Most cell lines showed little or no ill effect for several days after infection but a prominent cytopathic effect appeared in fibroblasts after 3-4 days. However, no viral DNA synthesis was detected and replication was abortive. Viral promoter activity during infection of nonpermissive cell types was assayed by RT-PCR. Early promoter activity was detectable in some, but not all cell types. In a liver and a colon carcinoma cell line, none of the promoters examined was significantly active, even when a higher multiplicity of infection was used. Major late promoter activity was not detectable in any cell type. The lack of DNA replication and MLP function suggests that a critical transition from early to late gene expression does not occur during abortive infection by OAV.

The murine coronavirus mouse hepatitis virus strain A59 from persistently infected murine cells exhibits an extended host range

In murine 17 Cl 1 cells persistently infected with murine coronavirus mouse hepatitis virus strain A59 (MHV-A59), expression of the virus receptor glycoprotein MHVR was markedly reduced (S. G. Sawicki, J. H. Lu, and K. V. Holmes, J. Virol. 69:5535-5543, 1995). Virus isolated from passage 600 of the persistently infected cells made smaller plaques on 17 Cl 1 cells than did MHV-A59. Unlike the parental MHV-A59, this variant virus also infected the BHK-21 (BHK) line of hamster cells. Virus plaque purified on BHK cells (MHV/BHK) grew more slowly in murine cells than did MHV-A59, and the rate of viral RNA synthesis was lower and the development of the viral nucleocapsid (N) protein was slower than those of MHV-A59. MHV/BHK was 100-fold more resistant to neutralization with the purified soluble recombinant MHV receptor glycoprotein (sMHVR) than was MHV-A59. Pretreatment of 17 Cl 1 cells with anti-MHVR monoclonal antibody CC1 protected the cells from infection with MHV-A59 but only partially protected them from infection with MHV/BHK. Thus, although MHV/BHK could still utilize MHVR as a receptor, its interactions with the receptor were significantly different from those of MHV-A59. To determine whether a hemagglutinin esterase (HE) glycoprotein that could bind the virions to 9-O-acetylated neuraminic acid moieties on the cell surface was expressed by MHV/BHK, an in situ esterase assay was used. No expression of HE activity was detected in 17 Cl 1 cells infected with MHV/BHK, suggesting that this virus, like MHV-A59, bound to cell membranes via its S glycoprotein. MHV/BHK was able to infect cell lines from many mammalian species, including murine (17 Cl 1), hamster (BHK), feline (Fcwf), bovine (MDBK), rat (RIE), monkey (Vero), and human (L132 and HeLa) cell lines. MHV/BHK could not infect dog kidney (MDCK I) or swine testis (ST) cell lines. Thus, in persistently infected murine cell lines that express very low levels of virus receptor MHVR and which also have and may express alternative virus receptors of lesser efficiency, there is a strong selective advantage for virus with altered interactions with receptor (D. S. Chen, M. Asanaka, F. S. Chen, J. E. Shively, and M. M. C. Lai, J. Virol. 71:1688-1691, 1997; D. S. Chen, M. Asanaka, K. Yokomori, F.-I. Wang, S. B. Hwang, H.-P. Li, and M. M. C. Lai, Proc. Natl. Acad. Sci. USA 92:12095-12099, 1995; P. Nedellec, G. S. Dveksler, E. Daniels, C. Turbide, B. Chow, A. A. Basile, K. V. Holmes, and N. Beauchemin, J. Virol. 68:4525-4537, 1994). Possibly, in coronavirus-infected animals, replication of the virus in tissues that express low levels of receptor might also select viruses with altered receptor recognition and extended host range.

Targeted adenovirus-mediated gene delivery to T cells via CD3

T cells are primary targets in numerous gene therapy protocols. However, the use of subgroup C adenovirus serotype 2 or 5 (Ad2 or Ad5) as a vector to transduce T cells is limited by its poor transduction efficiency for these cells. In this report we show that poor T-cell transduction results from these cells lacking both the primary Ad2-Ad5 receptor, used in attachment, and the secondary Ad receptor, which mediates entry of most adenovirus serotypes. These deficiencies were overcome by using a bispecific antibody (bsAb) with specificities for human CD3 and for a FLAG epitope genetically introduced into Ad5 (Ad.FLAG) to redirect the virus to human T cells. The anti-FLAG x anti-CD3 bsAb increased Ad.FLAG binding 30-fold, induced the efficient uptake of Ad.FLAG into the cells, and led to a 100- to 500-fold increase in the transduction of resting T cells. Moreover, fluorescence-activated cell sorter analysis showed that 25 to 90% of the T cells were transduced by the bsAb-complexed Ad.FLAG at multiplicities of infection between 20 and 100 active particles per cell. These results demonstrate that bsAbs can target Ad to non-Ad receptors on cells that are normally resistant to Ad, resulting in their efficient and specific transduction.

Selective targeting of human cells by a chimeric adenovirus vector containing a modified fiber protein

The adenovirus fiber protein is responsible for attachment of the virion to unidentified cell surface receptors. There are at least two distinct adenovirus fiber receptors which interact with the group B (Ad3) and group C (Ad5) adenoviruses. We have previously shown by using expressed adenovirus fiber proteins that it is possible to change the specificity of the fiber protein by exchanging the head domain with another serotype which recognizes a different receptor (S. C. Stevenson et al., J. Virol. 69:2850-2857, 1995). A chimeric fiber cDNA containing the Ad3 fiber head domain fused to the Ad5 fiber tail and shaft was incorporated into the genome of an adenovirus vector with E1 and E3 deleted encoding beta-galactosidase to generate Av9LacZ4, an adenovirus particle which contains a chimeric fiber protein. Western blot analysis of the chimeric fiber vector confirmed expression of the chimeric fiber protein and its association with the adenovirus capsid. Transduction experiments with fiber protein competitors demonstrated the altered receptor tropism of the chimeric fiber vector compared to that of the parental Av1LacZ4 vector. Transduction of a panel of human cell lines with the chimeric and parental vectors provided evidence for a different cellular distribution of the Ad5 and Ad3 receptors. Three cell lines (THP-1, MRC-5, and FaDu) were more efficiently transduced by the vector containing the Ad3 fiber head than by the Ad5 fiber vector. In contrast, human coronary artery endothelial cells were transduced more readily with the vector containing the Ad5 fiber than with the chimeric fiber vector. HeLa and human umbilical vein endothelial cells were transduced at equivalent levels compared with human diploid fibroblasts, which were refractory to transduction with both vectors. These results provide evidence for the differential expression of the Ad5 and Ad3 receptors on human cell lines derived from clinically relevant target tissues. Furthermore, we show that exchange of the fiber head domain is a viable approach to the production of adenovirus vectors with cell-type-selective transduction properties. It may be possible to extend this approach to the use of ligands for a range of different cellular receptors in order to target gene transfer to specific cell types at the level of transduction.

Adenovirus type 5 fiber knob binds to MHC class I alpha2 domain at the surface of human epithelial and B lymphoblastoid cells

Adenovirus serotype 5 (Ad5) fiber receptor was investigated using reverse antibody biopanning of a phage-displayed hexapeptide library, and virus-neutralizing monoclonal antibodies (mAbs 1D6.3 and 7A2.7) raised against recombinant Ad5 fiber knob. Both mAbs inhibited attachment of Ad5 to HeLa cells. Mimotopes of 1D6.3 showed homology with the C-terminal segment of the alpha2 domain of the heavy chain of human MHC class I molecules (MHC-I alpha2), and mimotopes of 7A2.7 were consensus to human fibronectin type III (FNIII) modules. In vitro, GST-fused MHC-I alpha2- and FNIII-derived oligopeptides interacted with recombinant fibers in a subgroup-specific manner. In vivo, the MHC-I alpha2 synthetic icosapeptide RAIVGFRVQWLRRYFVNGSR showed a net neutralization effect on Ad5 in HeLa cells, whereas the FNIII icosapeptide RHILWTPANTPAMGYLARVS significantly increased Ad5 binding to HeLa cells. Daudi cells, which lack surface expression of HLA class I molecules, showed a weak capacity for Ad5 binding. In beta2-microglobulin-transfected Daudi cells, Ad5 attachment and permissivity were restored to HeLa cell levels, with 4000 receptors per cell and a binding constant of 1.4x10(10)/M. The results suggested that the conserved region of MHC-I alpha2-domain including Trp167 represents a high affinity receptor for Ad5 fiber knob, whereas ubiquitous FNIII modules would serve as auxiliary receptors.