Bovine adenovirus type 3 internalization is independent of primary receptors of human adenovirus type 5 and porcine adenovirus type 3

Enhancement of mucosal innate and adaptive immunity following intranasal immunization of mice with a bovine adenoviral vector

Introduction

Nonhuman adenoviral (AdV) gene delivery platforms have significant value due to their ability to elude preexisting AdV vector immunity in most individuals. Previously, we have demonstrated that intranasal (IN) immunization of mice with BAd-H5HA, a bovine AdV type 3 (BAdV3) vector expressing H5N1 influenza virus hemagglutinin (HA), resulted in enhanced humoral and cell-mediated immune responses. The BAd-H5HA IN immunization resulted in complete protection following the challenge with an antigenically distinct H5N1 virus compared to the mouse group similarly immunized with HAd-H5HA, a human AdV type 5 (HAdV5) vector expressing HA.

Methods

Here, we attempted to determine the activation of innate immune responses in the lungs of mice inoculated intranasally with BAd-H5HA compared to the HAd-H5HA-inoculated group.

Results

RNA-Seq analyses of the lung tissues revealed differential expression (DE) of genes involved in innate and adaptive immunity in animals immunized with BAd-H5HA. The top ten enhanced genes were verified by RT-PCR. Consistently, there were transient increases in the levels of cytokines (IL-1α, IL-1β, IL-5, TNF- α, LIF, IL-17, G-CSF, MIP-1β, MCP-1, MIP-2, and GM-CSF) and toll-like receptors in the lungs of the group inoculated with BAdV vectors compared to that of the HAdV vector group.

Conclusion

These results demonstrate that the BAdV vectors induce enhanced innate and adaptive immunity-related factors compared to HAdV vectors in mice. Thus, the BAdV vector platform could be an excellent gene delivery system for recombinant vaccines and cancer immunotherapy.

A recombinant bovine adenoviral mucosal vaccine expressing mycobacterial antigen-85B generates robust protection against tuberculosis in mice

Although the BCG vaccine offers partial protection, tuberculosis remains a leading cause of infectious disease death, killing ∼1.5 million people annually. We developed mucosal vaccines expressing the autophagy-inducing peptide C5 and mycobacterial Ag85B-p25 epitope using replication-defective human adenovirus (HAdv85C5) and bovine adenovirus (BAdv85C5) vectors. BAdv85C5-infected dendritic cells (DCs) expressed a robust transcriptome of genes regulating antigen processing compared to HAdv85C5-infected DCs. BAdv85C5-infected DCs showed enhanced galectin-3/8 and autophagy-dependent in vitro Ag85B-p25 epitope presentation to CD4 T cells. BCG-vaccinated mice were intranasally boosted using HAdv85C5 or BAdv85C5 followed by infection using aerosolized Mycobacterium tuberculosis (Mtb). BAdv85C5 protected mice against tuberculosis both as a booster after BCG vaccine (>1.4-log10 reduction in Mtb lung burden) and as a single intranasal dose (>0.5-log10 reduction). Protection was associated with robust CD4 and CD8 effector (TEM), central memory (TCM), and CD103+/CD69+ lung-resident memory (TRM) T cell expansion, revealing BAdv85C5 as a promising mucosal vaccine for tuberculosis.

Nonhuman Adenoviral Vector-Based Platforms and Their Utility in Designing Next Generation of Vaccines for Infectious Diseases

Several human adenoviral (Ad) vectors have been developed for vaccine delivery owing to their numerous advantages, including the feasibility of different vector designs, the robustness of elicited immune responses, safety, and scalability. To expand the repertoire of Ad vectors for receptor usage and circumvention of Ad vector immunity, the use of less prevalent human Ad types or nonhuman Ads were explored for vector design. Notably, many nonhuman Ad vectors have shown great promise in preclinical and clinical studies as vectors for vaccine delivery. This review describes the key features of several nonhuman Ad vector platforms and their implications in developing effective vaccines against infectious diseases.

A potential approach for assessing the quality of human and nonhuman adenoviral vector preparations

Various types of human and nonhuman adenoviral (AdV) vectors are being used as gene delivery vectors in preclinical and clinical investigations. The objective of this study was to determine the ratio between the 2 best assays that would effectively address the variability in the titration of various AdV vectors in different cell lines and help obtain consistent results in preclinical and clinical studies using different AdV vectors. Here, we compared plaque-forming units, tissue culture infectious dose 50, focus-forming units (FFU), virus particle (VP) count, and genome copy number (GCN) of purified preparations of human AdV type C5, bovine AdV type 3, and porcine AdV type 3 to determine a correlation between infectious and noninfectious virus particles. Our results suggest that a VP:FFU or a VP:GCN ratio could accurately reflect the quality of an AdV preparation and could serve as an indicator to control batch-to-batch variability.

Prevalence and characteristics of a novel bovine adenovirus type 3 with a natural deletion fiber gene

Bovine adenovirus type 3 (BAdV-3) is an important pathogen causing bovine respiratory disease complex (BRDC). From Jun 2016 to Jun 2018, 108 nose swab samples were collected from cattle with BRDC from 11 farms in five cities, and 78.7% (85/108) samples were detected as BAdV-3 positive by Real-time PCR. Interestingly, the sequences of 7/10 fiber (852 bp) and hexon (785 bp) fragments cloned from 10 positive samples from eight farms were clustered into a single branch of the evolutionary tree. A BAdV-3 strain (BO/YB24/17/CH) was successfully isolated. The isolate caused pathological changes of lung, trachea and spleen in BALB/c mice. Notably, 79 amino acid deletions in the shaft domain and 74 unique amino acid mutations were found in the fiber gene of the isolate compared with the available complete sequences for fiber genes in the GenBank database. These characteristics indicated that the isolate may represent a novel fiber genotype of BAdV-3. A pair of specific primers covering the deletion region in the fiber gene was designed to screen the prevalence of BAdV-3 encoding the novel fiber gene. The results showed that 7 of the 10 strains possessed the novel fiber gene, and these novel fiber strains were detected from six farms in which calves were just imported from five provinces, indicating that this BAdV-3 with the natural deletion fiber gene has a wide geographical distribution in China. In conclusion, our results reveal that BAdV-3 is widespread in China and a pathogenic BAdV-3 strain with a novel fiber gene has been detected at high frequency, which is beneficial to understand the prevalence and genetic evolution of BAdV-3.

Characterization of a novel species of adenovirus from Japanese microbat and role of CXADR as its entry factor

Recently, bat adenoviruses (BtAdVs) of genus Mastadenovirus have been isolated from various bat species, some of them displaying a wide host range in cell culture. In this study, we isolated two BtAdVs from Japanese wild microbats. While one isolate was classified as Bat mastadenovirus A, the other was phylogenetically independent of other BtAdVs. It was rather related to, but serologically different from, canine adenoviruses. We propose that the latter, isolated from Asian parti-colored bat, should be assigned to a novel species of Bat mastadenovirus. Both isolates replicated in various mammalian cell lines, implying their wide cell tropism. To gain insight into cell tropism of these BtAdVs, we investigated the coxsackievirus and adenovirus receptor (CXADR) for virus entry to the cells. We prepared CXADR-knockout canine kidney cells and found that replication of BtAdVs was significantly hampered in these cells. For confirmation, their replication in canine CXADR-addback cells was rescued to the levels with the original cells. We also found that viral replication was corrected in human or bat CXADR-transduced cells to similar levels as in canine CXADR-addback cells. These results suggest that BtAdVs were able to use several mammalian-derived CXADRs as entry factors.

Current Use of Adenovirus Vectors and Their Production Methods

Various adenovirus (AdV) vector systems have proven to be lucrative options for gene delivery. They can serve as potential vaccine candidates for prevention of several common infectious diseases and hold the promise for gene therapy, especially for cancer. Several AdV vector-based therapies are currently at various stages of clinical trials worldwide, which make an immense interest of both the clinicians and researchers. Since these vectors are easy to manipulate, have broad tropism, and have the capability to yield high titers, this delivery system has a wide range of applications for different clinical settings. This chapter emphasizes on some of the current usages of AdV vectors and their production methods.

A Bovine Adenoviral Vector-Based H5N1 Influenza -Vaccine Provides Enhanced Immunogenicity and Protection at a Significantly Low Dose

Several human and nonhuman adenovirus (AdV) vectors including bovine AdV type 3 (BAdV-3) were developed as gene delivery vectors to supplement and/or elude human AdV (HAdV)-specific neutralizing antibodies (vector immunity). Here we evaluated the vaccine immunogenicity and efficacy of BAdV-3 vector (BAd-H5HA) expressing hemagglutinin (HA) of a H5N1 influenza virus in a dose escalation study in mice with the intranasal (IN) or intramuscular (IM) route of inoculation in comparison with the HAdV type C5 (HAdV-C5) vector (HAd-H5HA) expressing HA of a H5N1 influenza virus. Dose-related increases in the immune responses were clearly noticeable. A single IM inoculation with BAd-H5HA resulted in enhanced cellular immune responses compared with that of HAd-H5HA and conferred complete protection following challenge with a heterologous H5N1 virus at the dose of 3 × 10⁷ plaque-forming units (PFUs), whereas a significant amount of influenza virus was detected in the lungs of mice immunized with 1 × 10⁸ PFUs of HAd-H5HA. Similarly, compared with that of HAd-H5HA, a single IN inoculation with BAd-H5HA produced significantly enhanced humoral (HA-specific immunoglobulin [IgG] and its subclasses, as well as HA-specific IgA) and cellular immune responses, and conferred complete protection following challenge with a heterologous H5N1 virus. Complete protection with BAd-H5HA was observed with the lowest vaccine dose (1 × 10⁶ PFUs), but similar protection with HAd-H5HA was observed at the highest vaccine dose (1 × 10⁸ PFUs). These results suggest that at least 30-fold dose sparing can be achieved with BAd-H5HA vector compared with HAd-H5HA vaccine vector.

Safety profile of a replication-deficient human adenovirus-vectored foot-and-mouth disease virus serotype A24 subunit vaccine in cattle

The safety of a replication-deficient, human adenovirus-vectored foot-and-mouth disease virus (FMDV) serotype A24 Cruzeiro capsid-based subunit vaccine (AdtA24) was evaluated in five independent safety studies. The target animal safety studies were designed in compliance with United States (U.S.) regulatory requirements (Title 9, U.S. Code of Federal Regulation [9CFR]) and international standard guidelines (VICH Topic GL-44) for veterinary live vaccines. The first three studies were conducted in a total of 22 vaccinees and demonstrated that the AdtA24 master seed virus (MSV) was safe, did not revert to virulence and was not shed or spread from vaccinees to susceptible cattle or pigs. The fourth safety study conducted in 10 lactating cows using an AdtA24 vaccine serial showed that the vaccine was completely absent from milk. The fifth safety study was conducted under typical U.S. production field conditions in 500 healthy beef and dairy cattle using two AdtA24 vaccine serials. These results demonstrated that the vaccine was safe when used per the product label recommendations. Additional data collected during these five studies confirmed that AdtA24 vaccinees developed FMDV A24 and the HAd5 vaccine vector serum neutralization antibodies that test negative in a FMDV non-structural protein antibody test, confirming AdtA24 vaccine's capability to differentiate infected from vaccinated animals (DIVA). In conclusion, results from this comprehensive set of cattle studies demonstrated the safety of the replication-deficient AdtA24 vaccine and fulfilled safety-related requirements for U.S. regulatory requirements.

155R is a novel structural protein of bovine adenovirus type 3, but it is not essential for virus replication

Bovine adenovirus (AdV) type 3 (BAdV-3) E1 region shares functional homology with E1 of human AdV type C5. Sequence analysis of the BAdV-3 E1 region revealed the presence of a novel 155R ORF that is not observed in other AdVs, on the lower strand antiparallel to a portion of the E1B region. The 155R gene products in BAdV-3-infected cells were identified by Northern blot, reverse transcriptase PCR followed by sequencing and Western blot analysis using the155R-specific antibody. 155R seems to be a late protein and is present in purified BAdV-3 particles. Replication kinetics of BAdV mutants with either one (BAdV/155R/mt1) or two (BAdV/155R/mt2) stop codons in the 155R ORF were comparable to those of BAdV-3, indicating that 155R is not essential for virus replication in cell culture. These results suggest that 155R-deleted BAdV-3 vectors could be generated in a cell line that fully complements BAdV-3 E1 functions.

Ribosomal frameshifting and transcriptional slippage: From genetic steganography and cryptography to adventitious use

Genetic decoding is not ‘frozen’ as was earlier thought, but dynamic. One facet of this is frameshifting that often results in synthesis of a C-terminal region encoded by a new frame. Ribosomal frameshifting is utilized for the synthesis of additional products, for regulatory purposes and for translational ‘correction’ of problem or ‘savior’ indels. Utilization for synthesis of additional products occurs prominently in the decoding of mobile chromosomal element and viral genomes. One class of regulatory frameshifting of stable chromosomal genes governs cellular polyamine levels from yeasts to humans. In many cases of productively utilized frameshifting, the proportion of ribosomes that frameshift at a shift-prone site is enhanced by specific nascent peptide or mRNA context features. Such mRNA signals, which can be 5′ or 3′ of the shift site or both, can act by pairing with ribosomal RNA or as stem loops or pseudoknots even with one component being 4 kb 3′ from the shift site. Transcriptional realignment at slippage-prone sequences also generates productively utilized products encoded trans-frame with respect to the genomic sequence. This too can be enhanced by nucleic acid structure. Together with dynamic codon redefinition, frameshifting is one of the forms of recoding that enriches gene expression.

Xenogenic Adenoviral Vectors

Many nonhuman adenoviruses (AdVs) of simian, bovine, porcine, canine, ovine, murine, and fowl origin are being developed as gene delivery systems for recombinant vaccines and gene therapy applications. In addition to circumventing preexisting human AdV (HAdV) immunity, nonhuman AdV vectors utilize coxsackievirus-adenovirus receptor or other receptors for vector internalization, thereby expanding the range of cell types that can be targeted. Nonhuman AdV vectors also provide excellent platforms for veterinary vaccines. A specific nonhuman AdV vector when used in its species of origin could provide an excellent animal model for evaluating the vector efficacy and pathogenesis. These vectors are useful in prime–boost approaches with other AdV vectors or with other gene delivery systems including DNA immunization and viral or bacterial vectors. When multiple vector inoculations are required, nonhuman AdV vectors could supplement HAdV or other viral vectors.

RefSeq curation and annotation of antizyme and antizyme inhibitor genes in vertebrates

Polyamines are ubiquitous cations that are involved in regulating fundamental cellular processes such as cell growth and proliferation; hence, their intracellular concentration is tightly regulated. Antizyme and antizyme inhibitor have a central role in maintaining cellular polyamine levels. Antizyme is unique in that it is expressed via a novel programmed ribosomal frameshifting mechanism. Conventional computational tools are unable to predict a programmed frameshift, resulting in misannotation of antizyme transcripts and proteins on transcript and genomic sequences. Correct annotation of a programmed frameshifting event requires manual evaluation. Our goal was to provide an accurately curated and annotated Reference Sequence (RefSeq) data set of antizyme transcript and protein records across a broad taxonomic scope that would serve as standards for accurate representation of these gene products. As antizyme and antizyme inhibitor proteins are functionally connected, we also curated antizyme inhibitor genes to more fully represent the elegant biology of polyamine regulation. Manual review of genes for three members of the antizyme family and two members of the antizyme inhibitor family in 91 vertebrate organisms resulted in a total of 461 curated RefSeq records.

Circumventing antivector immunity: potential use of nonhuman adenoviral vectors

Adenoviruses are efficient gene delivery vectors based on their ability to transduce a wide variety of cell types and drive high-level transient transgene expression. While there have been advances in modifying human adenoviral (HAdV) vectors to increase their safety profile, there are still pitfalls that need to be further addressed. Preexisting humoral and cellular immunity against common HAdV serotypes limits the efficacy of gene transfer and duration of transgene expression. As an alternative, nonhuman AdV (NHAdV) vectors can circumvent neutralizing antibodies against HAdVs in immunized mice and monkeys and in human sera, suggesting that NHAdV vectors could circumvent preexisting humoral immunity against HAdVs in a clinical setting. Consequently, there has been an increased interest in developing NHAdV vectors for gene delivery in humans. In this review, we outline the recent advances and limitations of HAdV vectors for gene therapy and describe examples of NHAdV vectors focusing on their immunogenicity, tropism, and potential as effective gene therapy vehicles.

Mapping of nuclear import signal and importin α3 binding regions of 52K protein of bovine adenovirus-3

The L1 region of bovine adenovirus (BAdV)-3 encodes a non-structural protein designated 52K. Anti-52K serum detected a protein of 40kDa, which localized to the nucleus but not to the nucleolus in BAdV-3-infected or transfected cells. Analysis of mutant 52K proteins suggested that three basic residues ((105)RKR(107)) of the identified domain (amino acids (102)GMPRKRVLT(110)) are essential for nuclear localization of 52K. The nuclear import of a GST-52K fusion protein utilizes the classical importin α/β-dependent nuclear transport pathway. The 52K protein is preferentially bound to the cellular nuclear import receptor importin α3. Although deletion of amino acid 102-110 is sufficient to abrogate the nuclear localization of 52K, amino acid 90-133 are required for interaction with importin-α3 and localizing a cytoplasmic protein to the nucleus. These results suggest that 52K contains a bipartite NLS, which preferentially utilize an importin α3 nuclear import receptor-mediated pathway to transport 52K to the nucleus.

Emerging cancer vaccines: the promise of genetic vectors

Therapeutic vaccination against cancer is an important approach which, when combined with other therapies, can improve long-term control of cancer. In fact, the induction of adaptive immune responses against Tumor Associated Antigens (TAAs) as well as innate immunity are important factors for tumor stabilization/eradication. A variety of immunization technologies have been explored in last decades and are currently under active evaluation, such as cell-based, protein, peptide and heat-shock protein-based cancer vaccines. Genetic vaccines are emerging as promising methodologies to elicit immune responses against a wide variety of antigens, including TAAs. Amongst these, Adenovirus (Ad)-based vectors show excellent immunogenicity profile and have achieved immunological proof of concept in humans. In vivo electroporation of plasmid DNA (DNA-EP) is also a desirable vaccine technology for cancer vaccines, as it is repeatable several times, a parameter required for the long-term maintenance of anti-tumor immunity. Recent findings show that combinations of different modalities of immunization (heterologous prime/boost) are able to induce superior immune reactions as compared to single-modality vaccines. In this review, we will discuss the challenges and requirements of emerging cancer vaccines, particularly focusing on the genetic cancer vaccines currently under active development and the promise shown by Ad and DNA-EP heterologous prime-boost.

Persistence and the state of bovine and porcine adenoviral vector genomes in human and nonhuman cell lines

The state of vector genome in transduced cells influences the duration of transgene expression and can be a safety concern if it gets integrated randomly into the host genome. Although human adenovirus (Ad) serotype 5 (HAd5) mainly persists in a linear episomal form, information regarding the state of bovine Ad serotype 3 (BAd3) and porcine Ad serotype 3 (PAd3) vector genomes in human and nonhuman cells is currently unknown. To address this issue, MDA-MB-231 (human), MDBK (bovine), PK-15 (porcine), MT1A2 (mouse) and NIH-3T3 (mouse) cell lines were infected with replication-defective BAd3, PAd3 or HAd5 vectors carrying the green fluorescent protein (GFP) gene. The persistence and the state of vector genome were assessed by quantitative real-time PCR and Southern blot hybridization, respectively. Levels of transgene and Ad gene expressions were quantified using real-time RT-PCR. Persistence of BAd3 or PAd3 vectors was comparable to that of HAd5 vector. Only the linear episomal form of the vector genome was observed with each vector. In addition, expression levels of transgene as well as viral genes by all three vectors were comparable and correlated with their transduction levels in each cell type. These results indicate comparable biologic behavior of BAd3, PAd3 and HAd5 vectors in cell culture.

Evaluation of innate immunity and vector toxicity following inoculation of bovine, porcine or human adenoviral vectors in a mouse model

Nonhuman adenovirus (Ad) vectors derived from bovine Ad serotype 3 (BAd3) or porcine Ad serotype 3 (PAd3) can circumvent pre-existing immunity against human Ad (HAd). We have previously reported differential transduction of human and nonhuman cells by these Ad vectors, and their distinct receptor usage and biodistribution. To compare the induction of innate immunity, vector toxicity and vector uptake by Kupffer cells (KCs) following intravenous administration of PAd3, BAd3, or HAd5 vectors in mice, we determined mRNA expression levels of proinflammatory chemokines and cytokines, and Toll-like receptors (TLRs) in the liver and spleen. Tissue toxicity of these vectors was assessed by comparing serum levels of liver-specific enzymes, histopathology and Kupffer cell (KC) depletion. Compared to the HAd5 vector, PAd3 and BAd3 vectors were more potent stimulators of innate immune responses as indicated by enhanced mRNA expression of TLRs and proinflammatory chemokines and cytokine genes. Histopathological changes in the liver were most pronounced in HAd5-inoculated mice while BAd3- or PAd3-inoculated mice revealed mild histologic changes that were confined to early time points. Inoculation with HAd5 or PAd3 vectors resulted in a significant (P<0.05) decline of the number of KCs in the liver. Together, these results extend our previous observations regarding distinct in vivo biology of nonhuman and human Ad vectors.

Stimulation of -1 programmed ribosomal frameshifting by a metabolite-responsive RNA pseudoknot

Specific recognition of metabolites by functional RNA motifs within mRNAs has emerged as a crucial regulatory strategy for feedback control of biochemical reactions. Such riboswitches have been demonstrated to regulate different gene expression processes, including transcriptional termination and translational initiation in prokaryotic cells, as well as splicing in eukaryotic cells. The regulatory process is usually mediated by modulating the accessibility of specific sequence information of the expression platforms via metabolite-induced RNA conformational rearrangement. In eukaryotic systems, viral and the more limited number of cellular decoding -1 programmed ribosomal frameshifting (PRF) are commonly promoted by a 3' mRNA pseudoknot. In addition, such -1 PRF is generally constitutive rather than being regulatory, and usually results in a fixed ratio of products. We report here an RNA pseudoknot capable of stimulating -1 PRF whose efficiency can be tuned in response to the concentration of S-adenosylhomocysteine (SAH), and the improvement of its frameshifting efficiency by RNA engineering. In addition to providing an alternative approach for small-molecule regulation of gene expression in eukaryotic cells, such a metabolite-responsive pseudoknot suggests a plausible mechanism for metabolite-driven translational regulation of gene expression in eukaryotic systems.

Evaluation of cross-reactive cell-mediated immune responses among human, bovine and porcine adenoviruses

The absence of preexisting immunity against porcine adenovirus (Ad) serotype 3 (PAd3) and bovine Ad serotype 3 (BAd3) in humans makes them attractive alternatives to human Ad serotype 5 (HAd5) vectors. To determine whether there is significant cross-reactivity among HAd5, BAd3, and PAd3 at the level of cell-mediated immune responses, BALB/c mice were inoculated intraperitoneally with wild type (WT) or replication-defective (RD) HAd5, BAd3, or PAd3. Thirty-five days after the first inoculation, cross-reactive CD8+ cytotoxic T cells, as well as CD4+ Th1- and Th2-helper T cells, in the spleen were analyzed by ELISPOT, flow cytometry and cytotoxic T lymphocyte (CTL) assays. Virus neutralization assays were used to evaluate humoral cross-reactivity. CD8+ or CD4+ T cells primed with WT or RD HAd5, PAd3, or BAd3 demonstrated significant (P <0.005) reactivity with homologous Ad antigens, whereas, only minimal cross-reactivity was observed upon stimulation with heterologous Ad antigens. Ad-neutralizing antibodies were found to be homologous Ad-specific. Overall, these results suggest that there is no significant immunological cross-reactivity among HAd5, BAd3, and PAd3, thereby supporting the rationale for the use of BAd3 and PAd3 as alternative HAd vectors to circumvent anti-HAd immunity in humans.

Engineered adenovirus serotypes for overcoming anti-vector immunity

Adenovirus (Ad)-based gene transfer has been successfully utilised in gene therapy and vaccine applications. To date, an increasing number of human clinical trials utilise recombinant Ad-based vectors as a gene transfer platform. In particular, progress has been made recently in utilising Ad-based vectors as a vaccine platform in HIV, cancer immunotherapy approaches and in vaccination for other infections. Despite these successes, the scientific and bio-industrial communities have recently recognised that innate and pre-existing immunity against Ad vectors can constitute a serious obstacle to the development and application of this technology. It is essential to overcome vector-mediated immune responses, such as production of inflammatory cytokines and pre-existing immunity to Ad, because the induction of these responses not only shortens the period of gene expression but also leads to serious side effects. This review focuses on the biology of Ad infection and the approaches that are being adopted to overcome immunity against the Ad-based vectors.

Bovine adenovirus serotype 3 utilizes sialic acid as a cellular receptor for virus entry

Bovine adenovirus serotype 3 (BAd3) and porcine adenovirus serotype 3 (PAd3) entry into the host cells is independent of Coxsackievirus adenovirus receptor and integrins. The role of sialic acid in BAd3 and PAd3 entry was investigated. Removal of sialic acid by neuraminidase, or blocking sialic acid by wheat germ agglutinin lectin significantly inhibited BAd3, but not PAd3, transduction of Madin-Darby bovine kidney cells. Maackia amurensis agglutinin or Sambucus nigra (elder) agglutinin treatment efficiently blocked BAd3 transduction suggesting that BAd3 utilized alpha(2,3)-linked and alpha(2,6)-linked sialic acid as a cell receptor. BAd3 transduction of MDBK cells was sensitive to sodium periodate, bromelain, or trypsin treatment indicating that the receptor sialoconjugate was a glycoprotein rather than a ganglioside. To determine sialic acid-containing cell membrane proteins that bind to BAd3, virus overlay protein binding assay (VOPBA) was performed and showed that sialylated cell membrane proteins in size of approximately 97 and 34 kDa bind to BAd3. The results suggest that sialic acid serves as a primary receptor for BAd3.

Adenoviral vector-based strategies for cancer therapy

Definitive treatment of cancer has eluded scientists for decades. Current therapeutic modalities like surgery, chemotherapy, radiotherapy and receptor-targeted antibodies have varied degree of success and generally have moderate to severe side effects. Gene therapy is one of the novel and promising approaches for therapeutic intervention of cancer. Viral vectors in general and adenoviral (Ad) vectors in particular are efficient natural gene delivery systems and are one of the obvious choices for cancer gene therapy. Clinical and preclinical findings with a wide variety of approaches like tumor suppressor and suicide gene therapy, oncolysis, immunotherapy, anti-angiogenesis and RNA interference using Ad vectors have been quite promising, but there are still many hurdles to overcome. Shortcomings like increased immunogenicity, prevalence of preexisting anti-Ad immunity in human population and lack of specific targeting limit the clinical usefulness of Ad vectors. In recent years, extensive research efforts have been made to overcome these limitations through a variety of approaches including the use of conditionally-replicating Ad and specific targeting of tumor cells. In this review, we discuss the potential strengths and limitations of Ad vectors for cancer therapy.

Adenovirus receptors and their implications in gene delivery

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

Comparative analysis of vector biodistribution, persistence and gene expression following intravenous delivery of bovine, porcine and human adenoviral vectors in a mouse model

Nonhuman adenoviruses including bovine adenovirus serotype 3 (BAd3) and porcine adenovirus serotype 3 (PAd3) can circumvent pre-existing immunity against human adenovirus serotype 5 (HAd5) and are being developed as alternative vectors for gene delivery. To assess the usefulness of these vectors for in vivo gene delivery, we compared biodistribution, persistence, state of vector genome, and transgene and vector gene expression by replication-defective BAd3 and PAd3 vectors with those of HAd5 vector in a FVB/n mouse model following intravenous inoculation. BAd3 vector efficiently transduced the heart, kidney and lung in addition to the liver and spleen and persisted for a longer duration compared to PAd3 or HAd5 vectors. Biodistribution of PAd3 vector was comparable to that of HAd5 vector but showed more rapid vector clearance. Only linear episomal forms of BAd3, PAd3, and HAd5 vector genomes were detected. All three vectors efficiently expressed the green fluorescent protein (GFP) transgene proportionate to the vector genome copy number in various tissues. Furthermore, leaky expression of vector genes, both the early (E4) and the late (hexon) was observed in all three vectors and gradually declined with time. These results suggest that BAd3 and PAd3 vectors could serve as an alternative or supplement to HAd5 for gene delivery applications.

Usage of integrin and heparan sulfate as receptors for mouse adenovirus type 1

Adenovirus fiber knobs are the capsid components that interact with binding receptors on cells, while an Arg-Gly-Asp (RGD) sequence usually found in the penton base protein is important for the interaction of most adenoviruses with integrin entry receptors. Mouse adenovirus type 1 (MAV-1) lacks an RGD sequence in the virion penton base protein. We tested whether an RGD sequence found in the MAV-1 fiber knob plays a role in infection. Treatment of cells with a competitor RGD peptide or a purified recombinant RGD-containing fiber knob prior to infection resulted in reduced virus yields compared to those of controls, indicating the importance of the RGD sequence for infection. An investigation of the role of integrins as possible receptors showed that MAV-1 yields were reduced in the presence of EDTA, an inhibitor of integrin binding, and in the presence of anti-alpha(v) integrin antibody. Moreover, mouse embryo fibroblasts that were genetically deficient in alpha(v) integrin yielded less virus, supporting the hypothesis that alpha(v) integrin is a likely receptor for MAV-1. We also investigated whether glycosaminoglycans play a role in MAV-1 infection. Preincubation of MAV-1 with heparin, a heparan sulfate glycosaminoglycan analog, resulted in a decrease in MAV-1 virus yields. Reduced MAV-1 infectivity was also found with cells that genetically lack heparan sulfate or cells that were treated with heparinase I. Cumulatively, our data demonstrate that the RGD sequence in the MAV-1 fiber knob plays a role in infection by MAV-1, alpha(v) integrin acts as a receptor for the virus, and cell surface heparin sulfate glycosaminoglycans are important in MAV-1 infection.

Bovine adenoviral vector-based H5N1 influenza vaccine overcomes exceptionally high levels of pre-existing immunity against human adenovirus

Because of the high prevalence of adenovirus (Ad) infections in humans, it is believed that pre-existing Ad-neutralizing antibodies (vector immunity) may negatively impact the immune response to vaccine antigens when delivered by human Ad (HAd) vectors. In order to evaluate whether bovine Ad subtype 3 (BAd3), a non-HAd vector, can effectively elude high levels of pre-existing vector immunity, naïve and HAd serotype 5 (HAd)-primed mice were immunized with BAd-H5HA [BAd3 vector expressing the hemagglutinin (HA) gene from H5N1 influenza virus]. Even in the presence of very high levels of HAd-specific neutralizing antibody, no significant reductions in HA-specific humoral and cell-mediated immune (CMI) responses were observed in HAd-primed mice immunized with BAd-H5HA. In naïve mice immunized with HAd-H5HA (HAd5 vector expressing H5N1 HA) and boosted with BAd-H5HA, the humoral responses elicited were significantly higher (P < 0.01) than with either HAd-H5HA or BAd-H5HA alone, while the CMI responses were comparable in the groups. This finding underlines the importance of a heterologous prime-boost approach for achieving an enhanced immune response. The immunization of naïve or HAd-primed mice with BAd-H5HA bestowed full protection from morbidity and mortality following a potentially lethal challenge with A/Hong Kong/483/97. These results demonstrate the importance of BAd vectors as an alternate or supplement to HAd vectors for influenza pandemic preparedness.

A recoding element that stimulates decoding of UGA codons by Sec tRNA[Ser]Sec

Selenocysteine insertion during decoding of eukaryotic selenoprotein mRNA requires several trans-acting factors and a cis-acting selenocysteine insertion sequence (SECIS) usually located in the 3' UTR. A second cis-acting selenocysteine codon redefinition element (SRE) has recently been described that resides near the UGA-Sec codon of selenoprotein N (SEPN1). Similar phylogenetically conserved elements can be predicted in a subset of eukaryotic selenoprotein mRNAs. Previous experimental analysis of the SEPN1 SRE revealed it to have a stimulatory effect on readthrough of the UGA-Sec codon, which was not dependent upon the presence of a SECIS element in the 3' UTR; although, as expected, readthrough efficiency was further elevated by inclusion of a SECIS. In order to examine the nature of the redefinition event stimulated by the SEPN1 SRE, we have modified an experimentally tractable in vitro translation system that recapitulates efficient selenocysteine insertion. The results presented here illustrate that the SRE element has a stimulatory effect on decoding of the UGA-Sec codon by both the methylated and unmethylated isoforms of Sec tRNA([Ser]Sec), and confirm that efficient selenocysteine insertion is dependent on the presence of a 3'-UTR SECIS. The variation in recoding elements predicted near UGA-Sec codons implies that these elements may play a differential role in determining the amount of selenoprotein produced by acting as controllers of UGA decoding efficiency.

Expression of Coxsackie-Adenovirus receptor (CAR) in the developing mouse olfactory system

Interest in manipulating gene expression in olfactory sensory neurons (OSNs) has led to the use of adenoviruses (AdV) as gene delivery vectors. OSNs are the first order neurons in the olfactory system and the initial site of odor detection. They are highly susceptible to adenovirus infection although the mechanism is poorly understood. The Coxsackie-Adenovirus receptor (CAR) and members of the integrin family have been implicated in the process of AdV infection in various systems. Multiple serotypes of AdV efficiently bind to the CAR, leading to entry and infection of the host cell by a mechanism that can also involve integrins. Cell lines that do not express CAR are relatively resistant, but not completely immune to AdV infection, suggesting that other mechanisms participate in mediating AdV attachment and entry. Using in situ hybridization and western blot analyses, we show that OSNs and olfactory bulbs (OB) of mice express abundant CAR mRNA at embryonic and neonatal stages, with progressive diminution during postnatal development. By contrast to the olfactory epithelium (OE), CAR mRNA is still present in the adult mouse OB. Furthermore, despite a similar postnatal decline, CAR protein expression in the OE and OB of mice continues into adulthood. Our results suggest that the robust AdV infection observed in the postnatal olfactory system is mediated by CAR and that expression of even small amounts of CAR protein as seen in the adult rodent, permits efficient AdV infection and entry. CAR is an immunoglobulin domain-containing protein that bears homology to cell-adhesion molecules suggesting the possibility that it may participate in organization of the developing olfactory system.

Evolutionary specialization of recoding: frameshifting in the expression of S. cerevisiae antizyme mRNA is via an atypical antizyme shift site but is still +1

An autoregulatory translational shift to the +1 frame is required for the expression of ornithine decarboxylase antizyme from fungi to mammals. In most eukaryotes, including all vertebrates and a majority of the studied fungi/yeast, the site on antizyme mRNA where the shift occurs is UCC-UGA. The mechanism of the frameshift on this sequence likely involves nearly universal aspects of the eukaryotic translational machinery. Nevertheless, a mammalian antizyme frameshift cassette yields predominantly -2 frameshift in Saccharomyces cerevisiae, instead of the +1 in mammals. The recently identified endogenous S. cerevisiae antizyme mRNA has an atypical shift site: UGC-GCG-UGA. It is shown here that endogenous S. cerevisiae antizyme frameshifting is +1 rather than -2. We discuss how antizyme frameshifting in budding yeasts exploits peculiarities of their tRNA balance, and relate this to prior studies on Ty frameshifting.

Development of nonhuman adenoviruses as vaccine vectors

Human adenoviral (HAd) vectors have demonstrated great potential as vaccine vectors. Preclinical and clinical studies have demonstrated the feasibility of vector design, robust antigen expression and protective immunity using this system. However, clinical use of adenoviral vectors for vaccine purposes is anticipated to be limited by vector immunity that is either preexisting or develops rapidly following the first inoculation with adenoviral vectors. Vector immunity inactivates the vector particles and rapidly removes the transduced cells, thereby limiting the duration of transgene expression. Due to strong vector immunity, subsequent use of the same vector is usually less efficient. In order to circumvent this limitation, nonhuman adenoviral vectors have been proposed as alternative vectors. In addition to eluding HAd immunity, these vectors possess most of the attractive features of HAd vectors. Several replication-competent or replication-defective nonhuman adenoviral vectors have been developed and investigated for their potential as vaccine-delivery vectors. Here, we review recent advances in the design and characterization of various nonhuman adenoviral vectors, and discuss their potential applications for human and animal vaccination.