Identification of adenovirus (ad) penton base neutralizing epitopes by use of sera from patients who had received conditionally replicative ad (addl1520) for treatment of liver tumors

Viral Vectors in Gene Replacement Therapy

Throughout the years, several hundred million people with rare genetic disorders have been receiving only symptom management therapy. However, research and development efforts worldwide have led to the development of long-lasting, highly efficient, and safe gene therapy for a wide range of hereditary diseases. Improved viral vectors are now able to evade the preexisting immunity and more efficiently target and transduce therapeutically relevant cells, ensuring genome maintenance and expression of transgenes at the relevant levels. Hematological, ophthalmological, neurodegenerative, and metabolic therapeutic areas have witnessed successful treatment of hemophilia and muscular dystrophy, restoration of immune system in children with immunodeficiencies, and restoration of vision. This review focuses on three leading vector platforms of the past two decades: adeno-associated viruses (AAVs), adenoviruses (AdVs), and lentiviruses (LVs). Special attention is given to successful preclinical and clinical studies that have led to the approval of gene therapies: six AAV-based (Glybera® for lipoprotein lipase deficiency, Luxturna® for retinal dystrophy, Zolgensma® for spinal muscular atrophy, Upstaza® for AADC, Roctavian® for hemophilia A, and Hemgenix® for hemophilia B) and three LV-based (Libmeldy® for infantile metachromatic leukodystrophy, Zynteglo® for β-thalassemia, and Skysona® for ALD). The review also discusses the problems that arise in the development of gene therapy treatments, which, nevertheless, do not overshadow the successes of already developed gene therapies and the hope these treatments give to long-suffering patients and their families.

A humanized anti-human adenovirus 55 monoclonal antibody with good neutralization ability

Background

Human adenovirus type 55 (HAdV55) has a re-emerged as pathogen causing an acute respiratory disease presenting as a severe lower respiratory illness that can cause death. To date, there is no HAdV55 vaccine or treatment available for general use.

Methods

Herein, a monoclonal antibody specific for HAdV55, mAb 9-8, was isolated from an scFv-phage display library derived from mice immunized with the purified inactived-HAdV55 virions. By using ELISA and a virus micro-neutralization assay, we evaluated the binding and neutralizing activity of mAb 9-8 following humanization. Western blotting analysis and antigen-antibody molecular docking analysis were used to identify the antigenic epitopes that the humanized monoclonal antibody 9-8-h2 recognized. After that, their thermal stability was determined.

Results

MAb 9-8 showed potent neutralization activity against HAdV55. After humanization, the humanized neutralizing monoclonal antibody (9-8-h2) was identified to neutralize HAdV55 infection with an IC50 of 0.6050 nM. The mAb 9-8-h2 recognized HAdV55 and HAdV7 virus particles, but not HAdV4 particles. Although mAb 9-8-h2 could recognize HAdV7, it could not neutralize HAdV7. Furthermore, mAb 9-8-h2 recognized a conformational neutralization epitope of the fiber protein and the crucial amino acid residues (Arg 288, Asp 157, and Asn 200) were identified. MAb 9-8-h2 also showed favorable general physicochemical properties, including good thermostability and pH stability.

Conclusions

Overall, mAb 9-8-h2 might be a promising molecule for the prevention and treatment of HAdV55.

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

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

Capsid and Genome Modification Strategies to Reduce the Immunogenicity of Adenoviral Vectors

Adenovirus-based gene transfer vectors are the most frequently used vector type in gene therapy clinical trials to date, and they play an important role as genetic vaccine candidates during the ongoing SARS-CoV-2 pandemic. Immediately upon delivery, adenovirus-based vectors exhibit multiple complex vector-host interactions and induce innate and adaptive immune responses. This can severely limit their safety and efficacy, particularly after delivery through the blood stream. In this review article we summarize two strategies to modulate Ad vector-induced immune responses: extensive genomic and chemical capsid modifications. Both strategies have shown beneficial effects in a number of preclinical studies while potential synergistic effects warrant further investigations.

Adenovirus Vectors: Excellent Tools for Vaccine Development

Adenovirus was originally used as a vector for gene therapy. In recent years, with the development of the next-generation vectors with increased safety and high immunogenicity to transgene products, its utility as a vaccine vector has continued to increase. Adenovirus-based vaccines are currently being tested not only to prevent various infectious diseases but also to be applied as cancer vaccines. In this review, I discuss the innate and adaptive aspects of the immunological characteristics of adenovirus vectors and further examine the current status of advanced adenovirus-based vaccine development. Various methods that can overcome the limitations of currently used adenoviruses as vaccine vehicles are also discussed. Through this study, I hope that vaccine development using adenovirus vectors will be expedited and more successful.

Immunoinformatic construction of an adenovirus-based modular vaccine platform and its application in the design of a SARS-CoV-2 vaccine

The current SARS-CoV-2 pandemic has imposed new challenges and demands for health systems, especially in the development of new vaccine strategies. Vaccines for many pathogens were developed based on the display of foreign epitopes in the variable regions of the human adenovirus (HAdV) major capsid proteins (hexon, penton and fiber). The humoral immune response against the HAdV major capsid proteins was demonstrated to play a role in the development of an immune response against the epitopes in display. Through the immunoinformatic profiling of the major capsid proteins of HAdVs from different species, we developed a modular concept that can be used in the development of vaccines based on HAdV vectors. Our data suggests that different immunomodulatory potentials can be observed in the conserved regions, present in the hexon and penton proteins, from different species. Using this modular approach, we developed a HAdV-5 based vaccine strategy for SARS-CoV-2, constructed through the display of SARS-CoV-2 epitopes indicated by our prediction analysis as immunologically relevant. The sequences of the HAdV vector major capsid proteins were also edited to enhance the IFN-gamma induction and antigen presenting cells activation. This is the first study proposing a modular HAdV platform developed to aid the design of new vaccines by inducing an immune response more suited for the epitopes in display.

Pediatric Infections by Human mastadenovirus C Types 2, 89, and a Recombinant Type Detected in Japan between 2011 and 2018

Between 2011 and 2018, 518 respiratory adenovirus infections were diagnosed in a pediatric clinic in Shizuoka, Japan. Detection and typing were performed by partial sequencing of both hexon- and fiber-coding regions which identified: adenovirus type 1 (Ad-1, n = 85), Ad-2 (n = 160), Ad-3 (n = 193), Ad-4 (n = 18), Ad-5 (n = 27), Ad-11 (n = 2), Ad-54 (n = 3), and Ad-56 (n = 1). Considering previous reports of the circulation of an endemic recombinant Ad-2, e.g., Ad-89, 100 samples typed as Ad-2 were randomly selected for further molecular typing by sequencing the penton base-coding region. Despite the high nucleotide sequence conservation in the penton base- coding region, 27 samples showed 98% identity to Ad-2. Furthermore, 14 samples showed 97.7% identity to Ad-2 and 99.8% identity to Ad-89, while the remaining 13 samples showed an average 98% pairwise identity to other Ad-C types and clustered with Ad-5. The samples typed as Ad-89 (n = 14) and as a recombinant Ad type (P5H2F2) (n = 13) represented 27% of cases originally diagnosed as Ad-2, and were detected sporadically. Therefore, two previously uncharacterized types in Japan, Ad-89 and a recombinant Ad-C, were shown to circulate in children. This study creates a precedent to evaluate the epidemiology and divergence among Ad-C types by comprehensively considering the type classification of adenoviruses.

Molecular retargeting of antibodies converts immune defense against oncolytic viruses into cancer immunotherapy

Virus-neutralizing antibodies are a severe obstacle in oncolytic virotherapy. Here, we present a strategy to convert this unfavorable immune response into an anticancer immunotherapy via molecular retargeting. Application of a bifunctional adapter harboring a tumor-specific ligand and the adenovirus hexon domain DE1 for engaging antiadenoviral antibodies, attenuates tumor growth and prolongs survival in adenovirus-immunized mice. The therapeutic benefit achieved by tumor retargeting of antiviral antibodies is largely due to NK cell-mediated triggering of tumor-directed CD8 T-cells. We further demonstrate that antibody-retargeting (Ab-retargeting) is a feasible method to sensitize tumors to PD-1 immune checkpoint blockade. In therapeutic settings, Ab-retargeting greatly improves the outcome of intratumor application of an oncolytic adenovirus and facilitates long-term survival in treated animals when combined with PD-1 checkpoint inhibition. Tumor-directed retargeting of preexisting or virotherapy-induced antiviral antibodies therefore represents a promising strategy to fully exploit the immunotherapeutic potential of oncolytic virotherapy and checkpoint inhibition.

Antibodies against adenovirus fiber and penton base proteins inhibit adenovirus vector-mediated transduction in the liver following systemic administration

Pre-existing anti-adenovirus (Ad) neutralizing antibodies (AdNAbs) are a major barrier in clinical gene therapy using Ad vectors and oncolytic Ads; however, it has not been fully elucidated which Ad capsid protein-specific antibodies are involved in AdNAb-mediated inhibition of Ad infection in vivo. In this study, mice possessing antibodies specific for each Ad capsid protein were prepared by intramuscular electroporation of each Ad capsid protein-expressing plasmid. Ad vector-mediated hepatic transduction was efficiently inhibited by more than 100-fold in mice immunized with a fiber protein-expressing plasmid or a penton base-expressing plasmid. An Ad vector pre-coated with FX before administration mediated more than 100-fold lower transduction efficiencies in the liver of warfarinized mice immunized with a fiber protein-expressing plasmid or a penton base-expressing plasmid, compared with those in the liver of warfarinized non-immunized mice. These data suggest that anti-fiber protein and anti-penton base antibodies bind to an Ad vector even though FX has already bound to the hexon, and inhibit Ad vector-mediated transduction. This study provides important clues for the development of a novel Ad vector that can circumvent inhibition with AdNAbs.

Identification of adenovirus neutralizing antigens using capsid chimeric viruses

Human adenoviruses (HAdV) 3 and 7 can cause acute respiratory disease epidemics and outbreaks. Identification of neutralizing epitopes is vital for surveillance and vaccine development. In this study, we generated the recombinant capsid-chimeric human adenoviruses rAd3E-Fk7, containing the Ad3E backbone and the HAdV-7 fiber knob, and rAd3E-H7Fk7, which contain an Ad3E backbone but HAdV-7 hexon and fiber knob. In vitro neutralization tests with these chimeric adenoviruses using both mouse and human antisera indicated that hexon and fiber knob are the major targets recognized by neutralizing antibodies against HAdV-3 or HAdV-7, and other capsid proteins including the penton base and fiber shaft may not contribute to neutralizing antibody responses. In conclusion, both hexon and fiber knob structures in HAdV-3 and HAdV-7 may be the proteins which induce neutralizing antibody responses and thus may be important for adenovirus vaccine and drug development.

Comparative Genomic Analysis of Re-emergent Human Adenovirus Type 55 Pathogens Associated With Adult Severe Community-Acquired Pneumonia Reveals Conserved Genomes and Capsid Proteins

Human adenovirus type 55 (HAdV-B55) is a recently identified acute respiratory disease (ARD) pathogen in HAdV species B with a recombinant genome between renal HAdV-B11 and respiratory HAdV-B14. Since HAdV-B55 first appeared in China school in 2006, no more ARD cases associated with it had been reported until 2011, when there was an outbreak of adult severe community-acquired pneumonia (CAP) in Beijing, China. Reported here is the bioinformatics analysis of the re-emergent HAdV-B55 responsible for this outbreak. Recombination and protein sequence analysis re-confirmed that this isolate (BJ01) was a recombinant virus with the capsid hexon gene from HAdV-B11. The selection pressures for the three capsid proteins, i.e., hexon, penton base, and fiber genes, were all negative, along with very low non-synonymous (dN) and synonymous (dS) substitutions/site (<0.0007). Phylogenetic analyses of the whole genome and the three major capsid genes of HAdV-B55 revealed the close phylogenetic relationship among all HAdV-B55 strains. Comparative genomic analysis of this re-emergent HAdV-B55 strain (BJ01; 2011) with the first HAdV-B55 strain (QS-DLL; 2006) showed the high genome identity (99.87%), including 10 single-nucleotide non-synonymous substitutions, 11 synonymous substitutions, 3 insertions, and one deletion in non-coding regions. The major non-synonymous substitutions (6 of 10) occurred in the protein pVI in its L3 region, which protein has different functions at various stages of an adenovirus infection, and may be associated with the population distribution of HAdV-B55 infection. No non-synonymous substitutions were found in the three major capsid proteins, which proteins are responsible for type-specific neutralizing antibodies. Comparative genomic analysis of the re-emergent HAdV-B55 strains associated with adult severe CAP revealed conserved genome and capsid proteins, providing the foundation for the development of effective vaccines against this pathogen. This study also facilitates the further investigation of HAdV-B55 epidemiology, molecular evolution, patterns of pathogen emergence and re-emergence, and the predication of genome recombination between adenoviruses.

Hexon and fiber of adenovirus type 14 and 55 are major targets of neutralizing antibody but only fiber-specific antibody contributes to cross-neutralizing activity

Re-emerging human adenoviruses type 14 (HAdV14) and 55 (HAdV55) represent two highly virulent adenoviruses. The neutralizing antibody (nAb) responses elicited by infection or immunization remain largely unknown. Herein, we generated hexon-chimeric HAdV14 viruses harboring each single or entire hexon hyper-variable-regions (HVR) from HAdV55, and determined the neutralizing epitopes of human and mouse nAbs. In human sera, hexon-targeting nAbs are type-specific and mainly recognize HVR2, 5, and 7. Fiber-targeting nAbs are only detectable in sera cross-neutralizing HAdV14 and HAdV55 and contribute substantially to cross-neutralization. Penton-binding antibodies, however, show no significant neutralizing activities. In mice immunized with HAdV14 or HAdV55, a single immunization mainly elicited hexon-specific nAbs, which recognized HAdV14 HVR1, 2, and 7 and HAdV55 HVR1 and 2, respectively. After a booster immunization, cross-neutralizing fiber-specific nAbs became detectable. These results indicated that hexon elicits type-specific nAbs whereas fiber induces cross-neutralizing nAbs to HAdV14 and HAdV55, which are of significance in vaccine development.

Fowl adenovirus: history, emergence, biology and development of a vaccine against hydropericardium syndrome

The poultry industry has emerged as one of the largest and fastest growing public sectors in the developed and developing countries. Unfortunately, this industry is under a major threat from diseases that are viral (Newcastle disease, infectious bursal disease, influenza, hydropericardium syndrome), bacterial (colibacillosis, pasteurellosis, salmonellosis, mycoplasmosis), parasitic (coccidiosis, histoplasmosis) or nutritional (dyschondroplasia, osteoporosis). Among these diseases, hydropericardium syndrome (HPS) is one of the important emerging diseases occurring in the specific areas of the world where broilers (chickens) are reared under intensive conditions. HPS was first observed in 1987 at Angara Goth, an area near Karachi, Pakistan, where broilers are raised. Since then, HPS has been reported in many countries of the world. From these reported cases, an adenovirus that was either isolated from or visualized electron microscopically in the liver of affected broilers has been implicated in the syndrome. The syndrome has been reproduced by inoculation of isolated fowl adenovirus (FAdV) strains, and hence, the syndrome is also called infectious hydropericardium syndrome. To our knowledge, HPS has not been observed in humans, so it is not considered a zoonotic disease, but it is of economic importance and causes huge losses to the poultry industry. Efforts have been made to develop conventional vaccines against this disease, which were formulated from infected liver homogenate. Formalin-inactivated liver organ vaccines have failed to protect the poultry industry. Hence, there is a dire need to develop a suitable vaccine to combat this disease. Currently, recombinant vaccine candidates are being developed by using molecular biology and biotechnological approaches for the prevention and control of infectious diseases, including HPS. Therefore, it is suggested that the immunogenicity of these recombinant proteins should be evaluated for their use as subunit vaccines.

Insights into Adenovirus Uncoating from Interactions with Integrins and Mediators of Host Immunity

Human adenoviruses are large (150 MDa) nonenveloped double-stranded DNA (dsDNA) viruses that cause acute respiratory, gastrointestinal and ocular infections. Despite these disease associations, adenovirus has aided basic and clinical research efforts through studies of its association with cells and as a target of host antiviral responses. This review highlights the knowledge of adenovirus disassembly and nuclear transport gleaned from structural, biophysical and functional analyses of adenovirus interactions with soluble and membrane-associated host molecules.

Immune-Complexed Adenovirus Induce AIM2-Mediated Pyroptosis in Human Dendritic Cells

Human adenoviruses (HAdVs) are nonenveloped proteinaceous particles containing a linear double-stranded DNA genome. HAdVs cause a spectrum of pathologies in all populations regardless of health standards. Following repeat exposure to multiple HAdV types, we develop robust and long-lived humoral and cellular immune responses that provide life-long protection from de novo infections and persistent HAdV. How HAdVs, anti-HAdV antibodies and antigen presenting cells (APCs) interact to influence infection is still incompletely understood. In our study, we used physical, pharmacological, biochemical, fluorescence and electron microscopy, molecular and cell biology approaches to dissect the impact of immune-complexed HAdV (IC-HAdV) on human monocyte-derived dendritic cells (MoDCs). We show that IC-HAdV generate stabilized complexes of ~200 nm that are efficiently internalized by, and aggregate in, MoDCs. By comparing IC-HAdV, IC-empty capsid, IC-Ad2ts1 (a HAdV-C2 impaired in endosomal escape due to a mutation that impacts protease encapsidation) and IC-AdL40Q (a HAdV-C5 impaired in endosomal escape due to a mutation in protein VI), we demonstrate that protein VI-dependent endosomal escape is required for the HAdV genome to engage the DNA pattern recognition receptor AIM2 (absent in melanoma 2). AIM2 engagement induces pyroptotic MoDC death via ASC (apoptosis-associated speck protein containing a caspase activation/recruitment domain) aggregation, inflammasome formation, caspase 1 activation, and IL-1β and gasdermin D (GSDMD) cleavage. Our study provides mechanistic insight into how humoral immunity initiates an innate immune response to HAdV-C5 in human professional APCs.

Administration of Poly[di(sodium carboxylatoethylphenoxy)phosphazene] (PCEP) and Avian Beta Defensin as Adjuvants in Inactivated Inclusion Body Hepatitis Virus and its Hexon Protein-Based Experimental Vaccine Formulations in Chickens

Inclusion body hepatitis (IBH) is one of the major infectious diseases adversely affecting the poultry industry of the United States and Canada. Currently, no effective and safe vaccine is available for the control of IBH virus (IBHV) infection in chickens. However, based on the excellent safety and immunogenic profiles of experimental veterinary vaccines developed with the use of new generation adjuvants, we hypothesized that characterization of vaccine formulations containing inactivated IBHV or its capsid protein hexon as antigens, along with poly[di(sodium carboxylatoethylphenoxy)phosphazene] (PCEP) and avian beta defensin 2 (ABD2) as vaccine adjuvants, will be helpful in development of an effective and safe vaccine formulation for IBH. Our data demonstrated that experimental administration of vaccine formulations containing inactivated IBHV and a mixture of PCEP with or without ABD2 as an adjuvant induced significantly higher antibody responses compared with other vaccine formulations, while hexon protein-based vaccine formulations showed relatively lower levels of antibody responses. Thus, a vaccine formulation containing inactivated IBHV with PCEP or a mixture of PCEP and ABD2 (with a reduced dosage of PCEP) as an adjuvant may serve as a potential vaccine candidate. However, in order to overcome the risks associated with whole virus inactivated vaccines, characterization of additional viral capsid proteins, including fiber protein and penton of IBHV along with hexon protein in combination with more new generation adjuvants, will be helpful in further improvements of vaccines against IBHV infection.

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

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

Construction of new primer sets for corresponding to genetic evolution of human adenoviruses in major capsid genes through frequent recombination

A number of novel recombinant human adenoviruses (HAdVs) have recently been identified through sequencing of the complete genomes. The recombinant HAdV sequences share similarity with other types in the major capsid genes, namely the hexon, penton base, and fiber genes, implying recombination events, which may result in escape from the immune response and the acquisition of different organotropisms. Therefore, a surveillance system of HAdVs that considers the effect of frequent recombination on genetic evolution in these genes must be constructed. In this study, we designed new primer sets that can amplify the partial penton base and fiber genes from species HAdV-A to HAdV-F and proteotype HAdVs on the basis of sequence analyses, including previously reported primers that amplify loop 1 of the hexon. Phylogenetic analysis through sequencing with these primers correctly classified clinical HAdV isolates in loop 1 of the hexon gene, the Arg-Gly-Asp (RGD) loop of the penton base gene, and the knob of the fiber gene, which contain neutralizing, hemagglutination, and receptor binding epitopes associated with immunogenicity and tissue tropisms of HAdVs. This study contributes to the accumulation of correct information regarding genetic diversity and evolution in the worldwide HAdV surveillance.

Assessment of chimpanzee adenovirus serotype 63 neutralizing antibodies prior to evaluation of a candidate malaria vaccine regimen based on viral vectors

Prior to a chimpanzee adenovirus-based (ChAd63) malarial vaccine trial, sera were collected to assess ChAd63-specific neutralizing antibody titers in Banfora (Burkina Faso). The low neutralizing antibody titers reported in both adults and children (median titers, 139.1 and 35.0, respectively) are encouraging for the potential use of ChAd63 as a malarial vaccine vector.

Intertypic modular exchanges of genomic segments by homologous recombination at universally conserved segments in human adenovirus species D

Human adenovirus species D (HAdV-D), which is composed of clinically and epidemiologically important pathogens worldwide, contains more taxonomic "types" than any other species of the genus Mastadenovirus, although the mechanisms accounting for the high level of diversity remain to be disclosed. Recent studies of known and new types of HAdV-D have indicated that intertypic recombination between distant types contributes to the increasing diversity of the species. However, such findings raise the question as to how homologous recombination events occur between diversified types since homologous recombination is suppressed as nucleotide sequences diverge. In order to address this question, we investigated the distribution of the recombination boundaries in comparison with the landscape of intergenomic sequence conservation assessed according to the synonymous substitution rate (dS). The results revealed that specific genomic segments are conserved between even the most distantly related genomes; we call these segments "universally conserved segments" (UCSs). These findings suggest that UCSs facilitate homologous recombination, resulting in intergenomic segmental exchanges of UCS-flanking genomic regions as recombination modules. With the aid of such a mechanism, the haploid genomes of HAdV-Ds may have been reshuffled, resulting in chimeric genomes out of diversified repertoires in the HAdV-D population analogous to the MHC region reshuffled via crossing over in vertebrates. In addition, some HAdVs with chimeric genomes may have had the opportunity to avoid host immune responses thereby causing epidemics.

Adenovirus-based vaccines for fighting infectious diseases and cancer: progress in the field

The field of adenovirology is undergoing rapid change in response to increasing appreciation of the potential advantages of adenoviruses as the basis for new vaccines and as vectors for gene and cancer therapy. Substantial knowledge and understanding of adenoviruses at a molecular level has made their manipulation for use as vaccines and therapeutics relatively straightforward in comparison with other viral vectors. In this review we summarize the structure and life cycle of the adenovirus and focus on the use of adenovirus-based vectors in vaccines against infectious diseases and cancers. Strategies to overcome the problem of preexisting antiadenovirus immunity, which can hamper the immunogenicity of adenovirus-based vaccines, are discussed. When armed with tumor-associated antigens, replication-deficient and oncolytic adenoviruses can efficiently activate an antitumor immune response. We present concepts on how to use adenoviruses as therapeutic cancer vaccines and consider some of the strategies used to further improve antitumor immune responses. Studies that explore the prospect of adenoviruses as vaccines against infectious diseases and cancer are underway, and here we give an overview of the latest developments.

Directed evolution of mutator adenoviruses resistant to antibody neutralization

We incorporated a previously identified mutation that reduces the fidelity of the DNA polymerase into a human adenovirus vector. Using this mutator vector, we demonstrate rapid selection of resistance to a neutralizing anti-hexon monoclonal antibody due to a G434D mutation in hexon that precludes antibody binding. Since mutator adenoviruses can accumulate compound mutations that are unattainable using traditional random mutagenesis techniques, this approach will be valuable to the study of antivirals and host factor interactions.

A subunit vaccine against hydropericardium syndrome using adenovirus penton capsid protein

Hydropericardium syndrome (HPS) is a disease of poultry that is caused by fowl adenovirus-4. Inactivated liver homogenate from diseased birds is still the choice of vaccine in some countries which disseminates numerous pathogens along with inactivated virus. Moreover incomplete attenuation or inactivation, reversion to virulence and the oncogenic potential/genetic instability of the adenoviruses have prevented their use in routine vaccines. To address this problem an effort is made to develop a subunit vaccine. For this purpose penton base protein of HPS virus was expressed in Escherichia coli and used as subunit vaccine in broilers. Immunogenicity of the recombinant penton base protein and challenge protection test against pathogenic virus demonstrated the ability of recombinant penton base protein to confer (90%) protection. Results suggest that the recombinant penton base protein is a candidate for subunit vaccine against HPS.

Ad5:Ad48 hexon hypervariable region substitutions lead to toxicity and increased inflammatory responses following intravenous delivery

The development of adenoviral vectors for intravascular (i.v.) delivery will require improvements to their in vivo safety and efficacy. The hypervariable regions (HVRs) of the Ad5 hexon are a target for neutralizing antibodies, but also interact with factor X (FX), facilitating hepatocyte transduction. Ad48, a species D adenovirus, does not bind FX and has low seroprevalence. Therefore, it has been suggested that Ad5HVR48(1-7), a hexon-chimeric vector featuring the seven HVRs from Ad48, should display advantageous properties for gene therapy, by evading pre-existing Ad5 immunity and blocking FX interactions. We investigated the in vivo biodistribution of Ad5, Ad5HVR48(1-7), and Ad48 following i.v. delivery. Ad5HVR48(1-7) displayed reduced hepatocyte transduction and accumulation in Kupffer cells (KCs), but triggered a robust proinflammatory response, even at relatively low doses of vector. We detected elevated serum transaminases (48 hours) and increased numbers of periportal CD11b(+)/Gr-1(+) cells in the livers of Ad5HVR48(1-7)-treated animals following i.v., but not intramuscular (i.m.), delivery. In contrast, Ad48 did not elevate transaminases or result in the accumulation of CD11b(+)/Gr-1(+) cells. Collectively, these findings suggest that substantial hexon modifications can lead to unexpected properties which cannot be predicted from parental viruses. Therefore, refined mutations may be preferential for the successful development of targeted vector systems which require i.v. administration.

Circumventing antivector immunity by using adenovirus-infected blood cells for repeated application of adenovirus-vectored vaccines: proof of concept in rhesus macaques

Adenovirus has been extensively exploited as a vector platform for delivering vaccines. However, preexisting antiadenovirus immunity is the major stumbling block for application of adenovirus-vectored vaccines. In this study, we found that freshly isolated peripheral blood mononuclear cells (PBMCs), mostly CD14(+) cells, from adenovirus serotype 5 (Ad5)-seropositive primates (humans and rhesus macaques) can be efficiently infected with Ad5 in vitro. On the basis of this observation, a novel strategy based on adenoviral vector-infected PBMC (AVIP) immunization was explored to circumvent antivector immunity. Autologous infusion of Ad5-SIVgag-infected PBMCs elicited a strong Gag-specific cellular immune response but induced weaker Ad5-neutralizing antibody (NAb) in Ad5-seronegative macaques than in macaques intramuscularly injected with Ad5-SIVgag. Moreover, Ad5-seropositive macaques receiving multiple AVIP immunizations with Ad5-SIVenv, Ad5-SIVgag, and Ad5-SIVpol vaccines elicited escalated Env-, Gag-, and Pol-specific immune responses after each immunization that were significantly greater than those in macaques intramuscularly injected with these Ad5-SIV vaccines. After challenged intravenously with a highly pathogenic SIVmac239 virus, macaques receiving AVIP immunization demonstrated a significant reduction in viral load at both the peak time and set-point period compared with macaques without Ad5-SIV vaccines. Our study warranted further research and development of the AVIP immunization as a platform for repeated applications of adenovirus-vectored vaccines.

Comparison of two high-throughput assays for quantification of adenovirus type 5 neutralizing antibodies in a population of donors in China

Background

The presence of various levels of Adenovirus serotype 5 neutralizing antibodies (Ad5NAb) is thought to contribute to the inconsistent clinical results obtained from vaccination and gene therapy studies. Currently, two platforms based on high-throughput technology are available for Ad5NAb quantification, chemiluminescence- and fluorescence-based assays. The aim of this study was to compare the results of two assays in the seroepidemiology of Ad5NAb in a local population of donors.

Methodology/Principal Findings

The fluorescence-based neutralizing antibody detection test (FRNT) using recombinant Ad5-EGFP virus and the chemiluminescence-based neutralizing antibody test (CLNT) using Ad5-Fluc were developed and standardized for detecting the presence of Ad5NAb in serum samples from the population of donors in Beijing and Anhui provinces, China. First, the overall percentage of people positive for Ad5NAb performed by CLNT was higher than that obtained by FRNT (85.4 vs 69.9%, p<0.001). There was an 84.5% concordance between the two assays for the 206 samples tested (144 positive in both assays and 30 negative in both assays). All 32 discordant sera were CLNT-positive/FRNT-negative and were confirmed positive by western blot. Secondly, for all 144 sera positive by both assays, the two assays showed high correlation (r = 0.94, p<0.001) and close agreement (mean difference: 0.395 log₁₀, 95% CI: −0.054 log₁₀ to 0.845 log₁₀). Finally, it was found by both assays that there was no significant difference observed for titer or prevalence by gender (p = 0.503 vs 0.818, for two assays); however, age range (p = 0.049 vs 0.010) and geographic origin (p = 0.007 vs 0.011) were correlated with Ad5NAb prevalence in northern regions of China.

Conclusion

The CLNT assay was relatively more simple and had higher sensitivity than the FRNT assay for determining Ad5NAb titers. It is strongly suggested that the CLNT assay be used for future epidemiological studies of Ad5NAb in other localities.

Modification of Ad5 hexon hypervariable regions circumvents pre-existing Ad5 neutralizing antibodies and induces protective immune responses

The development of an effective malaria vaccine is a high global health priority. Vaccine vectors based on adenovirus type 5 are capable of generating robust and protective T cell and antibody responses in animal models and are currently being evaluated in clinical trials for HIV and malaria. They appear to be more effective in terms of inducing antigen-specific immune responses as compared with non-Ad5 serotype vectors. However, the high prevalence of neutralizing antibodies to Ad5 in the human population, particularly in the developing world, has the potential to limit the effectiveness of Ad5-based vaccines. We have generated novel Ad5-based vectors that precisely replace the hexon hypervariable regions with those derived from Ad43, a subgroup D serotype with low prevalence of neutralizing antibody in humans. We have demonstrated that these hexon-modified adenovectors are not neutralized efficiently by Ad5 neutralizing antibodies in vitro using sera from mice, rabbits and human volunteers. We have also generated hexon-modified adenovectors that express a rodent malaria parasite antigen, PyCSP, and demonstrated that they are as immunogenic as an unmodified vector. Furthermore, in contrast to the unmodified vector, the hexon-modified adenovectors induced robust T cell responses in mice with high levels of Ad5 neutralizing antibody. We also show that the hexon-modified vector can be combined with unmodified Ad5 vector in prime-boost regimens to induce protective responses in mice. Our data establish that these hexon-modified vectors are highly immunogenic even in the presence of pre-existing anti-adenovirus antibodies. These hexon-modified adenovectors may have advantages in sub-Saharan Africa where there is a high prevalence of Ad5 neutralizing antibody in the population.

Decreased pre-existing Ad5 capsid and Ad35 neutralizing antibodies increase HIV-1 infection risk in the Step trial independent of vaccination

Background

The Step trial raised the possibility that uncircumcised men with pre-existing Ad5 neutralizing antibodies carried an increased risk of HIV infection after vaccination. Thus, understanding Ad seropositivity in humans is important to the development of an AIDS vaccine. Here, we analyze the impact of different Ad5-specific neutralizing antibodies on immune function and clinical outcome.

Methods and Findings

Ad seropositivity in the Step trial volunteers was analyzed using chimeric rAd5/35 vectors to characterize their specificity for Ad5 fiber and non-fiber external (capsid) proteins. Immune responses and HIV seropositivity were correlated with the specificity of Ad5-neutralizing antibodies. Neutralizing antibodies induced by the vaccine in Ad5 seronegative subjects were directed preferentially to Ad5 capsid proteins, although some fiber-neutralizing antibodies could be detected. Pre-vaccination Ad5 serostatus did not affect the capsid-directed response after three vaccinations. In contrast, anti-fiber antibody titers were significantly higher in volunteers who were Ad5 seropositive prior to vaccination. Those Ad5 seropositive subjects who generated anti-capsid responses showed a marked reduction in vaccine-induced CD8 responses. Unexpectedly, anti-vector immunity differed qualitatively in Ad5 seropositive participants who became HIV-1 infected compared to uninfected case controls; Ad5 seropositive participants who later acquired HIV had lower neutralizing antibodies to capsid. Moreover, Ad35 seropositivity was decreased in HIV-infected subjects compared with uninfected case controls, while seroprevalence for other serotypes including Ad14, Ad28 and Ad41 was similar in both groups.

Conclusions

Together, these findings suggest that the case subjects were less immunologically responsive prior to infection. Subjects infected during the Step trial had qualitative differences in immunity that increased their risk of HIV-1 infection independent of vaccination.

Adenovirus serotype 5-specific neutralizing antibodies target multiple hexon hypervariable regions

The immunogenicity of adenovirus serotype 5 (Ad5) vectors has been shown to be suppressed by neutralizing antibodies (NAbs) directed primarily against the hexon hypervariable regions (HVRs). We previously reported that replacing all seven HVRs with those from the rare serotype virus Ad48 resulted in a chimeric Ad5HVR48(1-7) vector that largely evaded preexisting Ad5 immunity in mice and rhesus monkeys. In this study, we evaluated the extent to which Ad5-specific NAbs are directed against various HVRs. We constructed partial HVR-chimeric Ad5 vectors with only a subset of HVRs exchanged, and we utilized these vectors in both NAb assays and murine immunogenicity studies with and without baseline Ad5 immunity. Our results demonstrate that Ad5-specific NAbs target multiple HVRs, suggesting that replacing all HVRs is required to optimize evasion of anti-Ad5 immunity. These data have important implications for the development of novel vectors for both vaccines and gene therapy.

Adenovirus serotype 5 neutralizing antibodies target both hexon and fiber following vaccination and natural infection

The immunogenicity of adenovirus serotype 5 (Ad5) vectors has been shown to be suppressed by neutralizing antibodies (NAbs) directed primarily against the hexon hypervariable regions (HVRs). However, the role of NAbs directed against other capsid components, particularly the adenovirus fiber, remains unclear. Here we show that Ad5 NAbs target both hexon and fiber following vaccination and natural infection. Utilizing neutralization assays with capsid chimeric vectors, we observed that NAb responses to hexon appeared dominant and NAb responses against fiber were subdominant in sera from vaccinated mice, vaccinated humans, and naturally exposed humans. A novel chimeric Ad5 vector in which both the hexon HVRs and the fiber knob were exchanged nearly completely evaded Ad5-specific NAbs both in vitro and in vivo.

Construction and characterization of human adenovirus serotype 3 packaged by serotype 7 hexon

Human adenovirus serotype 3 (Ad3) and serotype 7 (Ad7) are important pathogens causing respiratory tract diseases such as acute respiratory disease in pediatric and adult patients, but the immunodominant targets of Ad3- and Ad7-specific neutralizing antibodies (NAbs) remain unclear. A chimeric Ad vector, Ad3/H7, was constructed by replacing the Ad3 hexon gene (H3) with the hexon gene (H7) of Ad7. The chimeric viruses were successfully rescued in HEp-2 cells, and the Ad7 hexon was able to encapsidate the Ad3 genome, and functioned as efficiently as the Ad3 hexon. Furthermore, we tested the host neutralization responses against the viruses using BALB/C mice. Up to 97% of the NAbs produced by mice that were infected with these viruses were specific for the hexon protein in vitro. Preimmunization of mice with one of Ad7 and Ad3/H7 significantly prevented subsequent intranasal infection of the other type in vivo. In contrast, preimmunization of mice with one of Ad3 and Ad3/H7 did not remarkably prevent subsequent infection of the other type. We next evaluated the functional significance of hexon and other structural proteins specific NAbs to suppress the immunogenicity of Ad3/H3 and Ad3/H7 vectors expressing EGFP in mice preimmunized with wild type Ad. Preimmunization of mice with Ad7 evidently suppressed EGFP-specific humoral immune responses elicited by Ad3/H7, and did not exert suppressive effects on Ad3/H3. But contrary to the in vitro neutralization results, EGFP-specific humoral immune responses elicited by Ad3/H7 was remarkably inhibited in Ad3-preimmunization mice. The whole genome of the Ad7 strain was sequenced and aligned with Ad3. The major differences between Ad3 and Ad7 were only observed in the fiber and hexon among all structural proteins, and the variation between the hexons only located in four hypervariable regions (HVRs), HVR-1, -2, -5, and -7. These results thus suggest that Ad3- and Ad7-specific NAbs are directed primarily against the hexon proteins both in vitro and in vivo. But high titer Ad3 fiber-specific NAbs may also play an important role in blunting Ad3 immunogenicity in vivo. These studies contribute to a more profound understanding of Ad immunogenicity and have relevance for the design of novel Ad vaccine.

Epidemiology of adenovirus type 5 neutralizing antibodies in healthy people and AIDS patients in Guangzhou, southern China

Recombinant adenovirus serotype 5 (Ad5) viruses have been extensively explored as vectors for vaccination or gene therapy. However, one major obstacle to their clinical application is the high prevalence of preexisting anti-Ad5 immunity resulting from natural infection. It has been reported that there are geographic variations in the prevalence of natural adenovirus infection. In the present study, we investigated the seroprevalence of Ad5 in Guangzhou, southern China by measuring the Ad5 neutralizing antibodies in blood samples collected from several sites. The seroprevalence was 77.34% in the general healthy population. The seroprevalence and antibody titers increased with age, with the older population (41-72 years old) having the highest seropositivity (84.8%) and percentage (54.4%) of high Ad5 neutralizing antibody titers (>1000). The dynamics of Ad5 neutralizing antibodies were stable and persistent over the course of eight months. Furthermore, the seroprevalence of Ad5 in the HIV-infected AIDS patients was investigated and there was no significant difference from the general healthy population. Our survey provides useful insights for the future development of Ad5-based vaccination and gene therapy.

Capsid-incorporation of antigens into adenovirus capsid proteins for a vaccine approach

Some viral vectors are potent inducers of cellular and humoral responses; therefore, viral vectors can be used to vaccinate against cancer or infectious diseases. This report will focus on adenovirus (Ad)-based vectors. Traditional viral-vector vaccination embodies the concept that the vector uses the host-cell machinery to express antigens that are encoded as transgenes within the viral vector. Several preclinical successes have used this approach in animal model systems. However, in some instances, these conventional Ad-based vaccines have yielded suboptimal clinical results. These suboptimal results are ascribed, in part, to preexisting Ad serotype 5 (Ad5) immunity. To address this issue, the "antigen capsid-incorporation" strategy has been developed to circumvent the drawbacks associated with conventional transgene expression of antigens by Ad vectors. This strategy embodies the incorporation of antigenic peptides within the capsid structure of viral vectors. Incorporating immunogenic peptides into the Ad capsid offers potential advantages. Importantly, vaccination by means of the antigen capsid-incorporated approach results in a strong humoral response, similar to the response generated by native Ad capsid proteins. This strategy also allows for the boosting of antigenic specific responses. This strategy may be the way forward for improved vaccine schemes, especially for those infections requiring a strong humoral antigenic response.

Osteosarcoma cells as carriers to allow antitumor activity of canine oncolytic adenovirus in the presence of neutralizing antibodies

Osteosarcoma (OSA) is the most common bone tumor affecting the dog. The veterinary options for therapeutic management of OSA are limited and prognosis for such patients is poor. Oncolytic adenoviruses are attractive tools for experimental therapeutics as they can replicate and spread within tumors to directly induce tumor destruction. However, a major impediment to systemic oncolytic adenoviruses injection is the presence of pre-existing neutralizing antibodies (Nabs). In this study, we investigated the effect of a replication-selective canine adenovirus (OCCAV) to treat OSA in the presence of Nabs and the use of canine OSA cells as carrier vehicles for evading Nabs. Our systemic biodistribution data indicated that canine tumor cells could successfully reach the tumor site and deliver OCCAV to tumor cells in an immunized mice model. Furthermore, the use of carrier cells also reduced adenovirus uptake by the liver. Importantly, OCCAV alone was not effective to control tumor growth in a pre-immunized xenograft mouse model. On the contrary, systemic antitumoral activity of carrier-cell OCCAV was evident even in the presence of circulating antibodies, which is a relevant result from a clinical point of view. These findings are of direct translational relevance for the future design of canine clinical trials.

The prevalence of antibodies to adenovirus serotype 5 in an adult Indian population and implications for adenovirus vector vaccines

In vivo gene delivery using human adenovirus serotype 5 (AdV5) vectors is being explored for vaccination purposes. The presence of anti-AdV5 antibodies in human serum arising from natural exposure to AdV5 can interfere potentially with and compromise the efficacy of rAdV5-based vaccine vectors. In this report, a collection of 114 sera from healthy adult Indian blood donors was analyzed for the presence of anti-AdV5 antibodies, using an AdV5 vector encoding the green fluorescent protein (GFP) to monitor the presence of anti-AdV5 neutralizing antibodies in human sera based on their ability to block virus entry into HeLa cells which express the Coxsackievirus-and-Adenovirus Receptor (CAR). In this assay all samples tested were positive for anti-AdV5 antibodies, with titers varying over a very wide range. It was also observed that these antibodies facilitated the uptake of the reporter AdV5 vector into the monocytic cell line U937 which does not express CAR, but expresses Fc receptors (FcRs) instead. These observations have implications for rAdV5-based vaccine development. J. Med. Virol. 82:407-414, 2010. (c) 2010 Wiley-Liss, Inc.

Adenovirus infections in solid organ transplant recipients

PURPOSE OF REVIEW

Adenoviruses are emerging as important viral pathogens in solid organ transplant recipients, impacting morbidity, graft survival and even mortality. This review will discuss the current understanding of the epidemiology, diagnosis and therapy of adenovirus infection in transplant recipients.

RECENT FINDINGS

Advances in the field include the use of polymerase chain reaction in the diagnosis of adenoviral infection, a better understanding of the epidemiology, immune response and potential new therapies, including preemptive and adoptive immunotherapy strategies. Adenoviral infections appear to be common, especially in pediatric solid organ transplant. Generally well tolerated, some high-risk patients may develop disseminated disease causing graft failure, which may lead to retransplant and/or death. Antiviral therapy and immunotherapy may play a role in these patients, although prospective controlled data are not available at this time.

SUMMARY

Although new tools and a better understanding of the epidemiology, risk factors and therapies for adenovirus are beginning to materialize, prospective, controlled trials, using careful definitions, and standardized methodologies need to be performed to more fully clarify these issues in solid organ transplant recipients.

Differential specificity and immunogenicity of adenovirus type 5 neutralizing antibodies elicited by natural infection or immunization

A recent clinical trial of a T-cell-based AIDS vaccine delivered with recombinant adenovirus type 5 (rAd5) vectors showed no efficacy in lowering viral load and was associated with increased risk of human immunodeficiency virus type 1 (HIV-1) infection. Preexisting immunity to Ad5 in humans could therefore affect both immunogenicity and vaccine efficacy. We hypothesized that vaccine-induced immunity is differentially affected, depending on whether subjects were exposed to Ad5 by natural infection or by vaccination. Serum samples from vaccine trial subjects receiving a DNA/rAd5 AIDS vaccine with or without prior immunity to Ad5 were examined for the specificity of their Ad5 neutralizing antibodies and their effect on HIV-1 immune responses. Here, we report that rAd5 neutralizing antibodies were directed to different components of the virion, depending on whether they were elicited by natural infection or vaccination in HIV vaccine trial subjects. Neutralizing antibodies elicited by natural infection were directed largely to the Ad5 fiber, while exposure to rAd5 through vaccination elicited antibodies primarily to capsid proteins other than fiber. Notably, preexisting immunity to Ad5 fiber from natural infection significantly reduced the CD4 and CD8 cell responses to HIV Gag after DNA/rAd5 vaccination. The specificity of Ad5 neutralizing antibodies therefore differs depending on the route of exposure, and natural Ad5 infection compromises Ad5 vaccine-induced immunity to weak immunogens, such as HIV-1 Gag. These results have implications for future AIDS vaccine trials and the design of next-generation gene-based vaccine vectors.

Fiber mediated receptor masking in non-infected bystander cells restricts adenovirus cell killing effect but promotes adenovirus host co-existence

The basic concept of conditionally replicating adenoviruses (CRAD) as oncolytic agents is that progenies generated from each round of infection will disperse, infect and kill new cancer cells. However, CRAD has only inhibited, but not eradicated tumor growth in xenograft tumor therapy, and CRAD therapy has had only marginal clinical benefit to cancer patients. Here, we found that CRAD propagation and cancer cell survival co-existed for long periods of time when infection was initiated at low multiplicity of infection (MOI), and cancer cell killing was inefficient and slow compared to the assumed cell killing effect upon infection at high MOI. Excessive production of fiber molecules from initial CRAD infection of only 1 to 2% cancer cells and their release prior to the viral particle itself caused a tropism-specific receptor masking in both infected and non-infected bystander cells. Consequently, the non-infected bystander cells were inefficiently bound and infected by CRAD progenies. Further, fiber overproduction with concomitant restriction of adenovirus spread was observed in xenograft cancer therapy models. Besides the CAR-binding Ad4, Ad5, and Ad37, infection with CD46-binding Ad35 and Ad11 also caused receptor masking. Fiber overproduction and its resulting receptor masking thus play a key role in limiting CRAD functionality, but potentially promote adenovirus and host cell co-existence. These findings also give important clues for understanding mechanisms underlying the natural infection course of various adenoviruses.

Vault nanoparticles containing an adenovirus-derived membrane lytic protein facilitate toxin and gene transfer

Nonviral methods of gene delivery possess several advantages over that of viral-based vectors, including having increased safety. However, the ability to achieve effective transport of therapeutic molecules across host cell membranes via nonviral methods remains a significant goal. Cell-derived nanoparticles known as vaults have been proposed as novel candidate transfer vehicles for various foreign molecules. Recombinant vault particles enter cells via macropinocytosis or phagocytosis but lack demonstrable membrane penetrating activity. To explore the feasibility of improving vault penetration into target cells, we incorporated the membrane lytic domain of adenovirus protein VI (pVI) into the interior of recombinant vault particles via fusion to the vault poly(ADP-ribose) polymerase (VPARP) interaction domain. The membrane lytic activity of the pVI domain was retained upon incorporation into vault particles. Moreover, internalization of vault-pVI complexes into murine macrophages promoted co-delivery of a soluble ribotoxin or a cDNA plasmid encoding GFP. These findings indicate that vault particles can be modified to enhance cell transfer of selected biomolecules.

Adenoviruses: update on structure and function

Adenoviruses have been studied intensively for over 50 years as models of virus-cell interactions and latterly as gene vectors. With the advent of more sophisticated structural analysis techniques the disposition of most of the 13 structural proteins have been defined to a reasonable level. This review seeks to describe the functional properties of these proteins and shows that they all have a part to play in deciding the outcome of an infection and act at every level of the virus's path through the host cell. They are primarily involved in the induction of the different arms of the immune system and a better understanding of their overall properties should lead to more effective ways of combating virus infections.

Clinical features and treatment of adenovirus infections

Adenoviruses (Ads) are common opportunistic pathogens that are rarely associated with severe clinical symptoms in healthy individuals. In contrast, in patients with compromised immunity, Ad infections often result in disseminated and potentially life-threatening disease. Among these are AIDS patients, individuals with hereditary immunodeficiencies and recipients of solid organ or haematopoietic stem cell transplants (HSCT) who receive immunosuppressive therapy. The latter account for the largest number of severe Ad infections. There is currently no formally approved antiviral therapy for the treatment of severe Ad keratoconjunctivitis and life-threatening Ad infections in immunocompromised patients. Here we update current knowledge on Ad biology, the clinical features observed in different patient groups and specific immune responses towards Ad infections. In addition, we review current and future treatment options, including: (i) the antiviral drugs cidofovir, ribavirin and new investigational compounds, as evaluated in the clinic or in relevant animal models, as well as (ii) novel immunotherapeutic strategies.

Neutralizing antibody blocks adenovirus infection by arresting microtubule-dependent cytoplasmic transport

Neutralizing antibodies are commonly elicited by viral infection. Most antibodies that have been characterized block early stages of virus entry that occur before membrane penetration, whereas inhibition of late stages in entry that occurs after membrane penetration has been poorly characterized. Here we provide evidence that the neutralizing antihexon monoclonal antibody 9C12 inhibits adenovirus infection by blocking microtubule-dependent translocation of the virus to the microtubule-organizing center following endosome penetration. These studies identify a previously undescribed mechanism by which neutralizing antibodies block virus infection, a situation that may be relevant for other nonenveloped viruses that use microtubule-dependent transport during cell entry.

Epitopes expressed in different adenovirus capsid proteins induce different levels of epitope-specific immunity

On the basis of the concept that the capsid proteins of adenovirus (Ad) gene transfer vectors can be genetically manipulated to enhance the immunogenicity of Ad-based vaccines, the present study compared the antiantigen immunogenicity of Ad vectors with a common epitope of the hemagglutinin (HA) protein of the influenza A virus incorporated into the outer Ad capsid protein hexon, penton base, fiber knob, or protein IX. Incorporation of the same epitope into the different capsid proteins provided insights into the correlation between epitope position and antiepitope immunity. Following immunization of three different strains of mice (C57BL/6, BALB/c, and CBA) with either an equal number of Ad particles (resulting in a different total HA copy number) or different Ad particle numbers (to achieve the same HA copy number), the highest primary (immunoglobulin M [IgM]) and secondary (IgG) anti-HA humoral and cellular CD4 gamma interferon and interleukin-4 responses against HA were always achieved with the Ad vector carrying the HA epitope in fiber knob. These observations suggest that the immune response against an epitope inserted into Ad capsid proteins is not necessarily dependent on the capsid protein number and imply that the choice of incorporation site in Ad capsid proteins in their use as vaccines needs to be compared in vivo.

Seroprevalence of neutralizing antibodies to adenovirus type 5 among children in India: implications for recombinant adenovirus-based vaccines

We determined the levels of adenovirus 5 (Ad5) neutralizing antibodies in children in India less than 2 years of age. The results clearly show an age-dependent increase in Ad5-specific immunity, with 7- to 12-month-old children having the lowest levels of Ad5 immunity. This opens up the scope for the use of recombinant Ad5-based vaccines in this age group.

Phylogenetic analysis and structural predictions of human adenovirus penton proteins as a basis for tissue-specific adenovirus vector design

The penton base is a major capsid protein of human adenoviruses (HAdV) which forms the vertices of the capsid and interacts with hexon and fiber protein. Two hypervariable loops of the penton are exposed on the capsid surface. Sequences of these and 300 adjacent amino acid residues of all 51 HAdV and closely related simian adenoviruses were studied. Adjacent sequences and predicted overall secondary structure were conserved. Phylogenetic analysis revealed clustering corresponding to the HAdV species and recombination events in the origin of HAdV prototypes. All HAdV except serotypes 40 and 41 of species F exhibited an integrin binding RGD motif in the second loop. The lengths of the loops (HVR1 and RGD loops) varied significantly between HAdV species with the longest RGD loop observed in species C and the longest HVR1 in species B. Long loops may permit the insertion of motifs that modify tissue tropism. Genetic analysis of HAdV prime strain p17'H30, a neutralization variant of HAdV-D17, indicated the significance of nonhexon neutralization epitopes for HAdV immune escape. Fourteen highly conserved motifs of the penton base were analyzed by site-directed mutagenesis of HAdV-D8 and tested for sustained induction of early cytopathic effects. Thus, three new motifs essential for penton base function were identified additionally to the RGD site, which interacts with a secondary cellular receptor responsible for internalization. Therefore, our penton primary structure data and secondary structure modeling in combination with the recently published fiber knob sequences may permit the rational design of tissue-specific adenoviral vectors.

Decreased immune reactivity towards a knobless, affibody-targeted adenovirus type 5 vector

In this study, a prototype Adenovirus type 5 (Ad5) vector deleted of the fiber knob domain and carrying an Affibody molecule as the targeting ligand showed decreased susceptibility to human pre-existing antibodies. This vector, Ad5/R7-Z(taq)Z(taq), has short fibers carrying seven shaft repeats, a non-native trimerization signal and an affibody molecule (Z(taq)) reactive to Taq polymerase. Ad5/R7-Z(taq)Z(taq) could be specifically targeted to 293 cells stably expressing membrane-bound anti-Z(taq) idiotypic affibody called Z(ztaq) (293Z(ztaq)). Sera from 50 blood donors were analyzed for neutralization activity (NA) against the parental Ad5/Fiwt vector and knobless Ad5/R7-Z(taq)Z(taq) on 293Z(ztaq) cells. Twenty-three sera had NA titers (> or =1:64) against Ad5/Fiwt (46%) and only two against Ad5/R7-Z(taq)Z(taq) (4%). Characterization of sera with NA titers showed that the knob domain is one of the targets of the antibodies. Neutralization assays using sera pre-adsorbed on knob and hexon proteins showed that the NA of the sera was carried mainly by anti-knob and anti-hexon antibodies, but in certain sera the anti-hexon antibodies represent the major population of the neutralizing antibodies (NAbs). Our results suggested that a combination of knob deletion and hexon switching could be an effective strategy for Ad vectors to better evade the anti-Ad NAbs.

Biological activities of a recombinant adenovirus p53 (SCH 58500) administered by hepatic arterial infusion in a Phase 1 colorectal cancer trial

The major focus of intrahepatic arterial (IHA) administration of adenoviruses (Ad) has been on safety. Currently, there is little published data on the biological responses to Ad when administered via this route. As part of a Phase I study, we evaluated biological responses to a replication-defective adenovirus encoding the p53 transgene (SCH 58500) when administered by hepatic arterial infusion to patients with primarily colorectal cancer metastatic to the liver. In analyzing biological responses to the Ad vector, we found that both total and neutralizing Ad antibodies increased weeks after SCH 58500 infusion. The fold increase in antibody titers was not dependent on SCH 58500 dosage. The proinflammatory cytokine interleukin-6 (IL-6) transiently peaked within 6 h of dosing. The cytokine sTNF-R2 showed elevation by 24 h post-treatment, and fold increases were directly related to SCH 58500 doses. Cytokines TNF-alpha, IL-1beta, and sTNF-R1 showed no increased levels over 24 h. Predose antibody levels did not appear to predict transduction, nor did serum Ad neutralizing factor (SNF). Delivery of SCH 58500 to tumor tissue occurred, though we found distribution more predominantly in liver tissues, as opposed to tumors. RT-PCR showed significantly higher expression levels (P<0.0001, ANOVA) for adenovirus type 2 and 5 receptor (CAR) in liver tissues, suggesting a correlation with transduction. Evidence of tumor-specific apoptotic activity was provided by laser scanning cytometry, which determined a coincidence of elevated nuclear p53 protein expression with apoptosis in patient tissue. IHA administration of a replication defective adenovirus is a feasible mode of delivery, allowing for exogenous transfer of the p53 gene into target tissues, with evidence of functional p53. Limited and transient inflammatory responses to the drug occurred, but pre-existing immunity to Ad did not preclude SCH 58500 delivery.