Characteristics of neutralizing antibodies to adenovirus capsid proteins in human and animal sera

Characterization of Pre-Existing Neutralizing Antibody to Human Adenovirus Types 5 and 49 and Simian Type 23 in Chinese Population

Recombinant adenovirus vector has been widely used in vaccine development. Due to the pre-existing immunity of human adenovirus type 5 (HAd5) in humans, a range of rare human and chimpanzee adenovirus vectors have been developed. In the previous study, we constructed novel adenovirus vector Sad23L and Ad49L based on simian adenovirus type 23 (SAd23) and human adenovirus type 49 (HAd49), which were used in the development of ZIKV and COVID-19 vaccines. However, the levels of pre-existing neutralizing antibody (NAb) of HAd49 and SAd23 remain unclear in China. In this study, we measured NAbs titers of HAd5, HAd49, and SAd23 in 600 healthy blood donors from 6 regions across China. NAb titer of HAd49 or SAd23 was significantly lower than that of HAd5 (p < 0.001). There was no significant difference in seroprevalence and NAb titers of three adenoviruses between male and female donors. The seropositive rates of HAd5 and SAd23 increased with age growth in a positive correlation (p < 0.01), while in contrast to HAd5, HAd49, and SAd23 had a low level of pre-existing immunity in Chinese population, which suggested that Ad49L and Sad23L vectors could be used in vaccine development for humans.

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 7 virus-like particle vaccine induces Dendritic cell maturation through the TLR4/NF-κB pathway and is highly immunogenic

Human adenovirus type 7 (HAdv-7) infection is the main cause of upper respiratory tract infection, bronchitis and pneumonia in children. At present, there are no anti-adenovirus drugs or preventive vaccines in the market. Therefore, it is necessary to develop a safe and effective anti-adenovirus type 7 vaccine. In this study, we designed a virus-like particle vaccine expressing the epitopes of hexon and penton of adenovirus type 7 with hepatitis B core protein (HBc) as the vector to induce high-level humoral and cellular immune responses. To evaluate the effectiveness of the vaccine, we first detected the expression of molecular markers on the surface of antigen presenting cells and the secretion of proinflammatory cytokines in vitro. We then measured the levels of neutralizing antibodies and T cell activation in vivo. The results showed that the HAdv-7 virus-like particles (VLPs) recombinant subunit vaccine could activate the innate immune response, including the TLR4/NF-κB pathway which upregulated the expression of MHC II, CD80, CD86, CD40 and cytokines. The vaccine also triggered a strong neutralizing antibody and cellular immune response and activated T lymphocytes. Therefore, the HAdv-7 VLPs promoted humoral and cellular immune responses, thereby potentially enhancing protection against HAdv-7 infection.

Molecular Mechanism of Adenovirus Late Protein L4-100K Chaperones the Trimerization of Hexon

Assembly of the adenovirus capsid protein hexon depends on the assistance of the molecular chaperone L4-100K. However, the chaperone mechanisms remain unclear. In this study, we found that L4-100K was involved in the hexon translation process and could prevent hexon degradation by the proteasome in cotransfected human cells. Two nonadjacent domains, 84-133 and 656-697, at the N-terminal and C-terminal regions of human adenovirus type 5 L4-100K, respectively, were found to be crucial and cooperatively responsible for hexon trimer expression and assembly. These two chaperone-related domains were conserved in the sequence of L4-100K and in the function of hexon assembly across different adenovirus serotypes. Different degrees of cross-activity of hexon trimerization with different serotypes were detected in subgroups B, C, and D, which were proven to be controlled by the interaction between the C-terminal chaperone-related domain of L4-100K and hypervariable regions (HVR) of hexon. Additionally, HVR-chimeric hexon mutants were successfully assembled with the assistance of the 1-697 mutant. Structural analysis of 656-697 by nuclear magnetic resonance and structural prediction of L4-100K using Robetta showed that the two conserved domains are mainly composed of α-helices and are located on the surface of the highly folded core region. Our research provides a more complete understanding of hexon assembly and guidance for the development of hexon-chimeric adenovirus vectors that will be safer, smarter, and more efficient. IMPORTANCE Adenovirus vectors have been widely used in clinical trials of vaccines and gene therapy, although some deficiencies remain. Chimeric modification of the hexon was expected to improve the potency of preexisting immune evasion and targeting, but in many cases, viral packaging is prevented by the inability of the chimeric hexon to assemble correctly. So far, few studies have examined the mechanisms of hexon trimer assembly. Here, we show how the chaperone protein L4-100K contributes to the assembly of the adenovirus capsid protein hexon, and these data will provide a guide for novel adenovirus vector design and development, as we desired.

An Old Acquaintance: Could Adenoviruses Be Our Next Pandemic Threat?

Human adenoviruses (HAdV) are one of the most important pathogens detected in acute respiratory diseases in pediatrics and immunocompromised patients. In 1953, Wallace Rowe described it for the first time in oropharyngeal lymphatic tissue. To date, more than 110 types of HAdV have been described, with different cellular tropisms. They can cause respiratory and gastrointestinal symptoms, even urinary tract inflammation, although most infections are asymptomatic. However, there is a population at risk that can develop serious and even lethal conditions. These viruses have a double-stranded DNA genome, 25-48 kbp, 90 nm in diameter, without a mantle, are stable in the environment, and resistant to fat-soluble detergents. Currently the diagnosis is made with lateral flow immunochromatography or molecular biology through a polymerase chain reaction. This review aimed to highlight the HAdV variability and the pandemic potential that a HAdV3 and 7 recombinant could have considering the aggressive outbreaks produced in health facilities. Herein, we described the characteristics of HAdV, from the infection to treatment, vaccine development, and the evaluation of the social determinants of health associated with HAdV, suggesting the necessary measures for future sanitary control to prevent disasters such as the SARS-CoV-2 pandemic, with an emphasis on the use of recombinant AdV vaccines to control other potential pandemics.

Human adenovirus type 7 subunit vaccine induces dendritic cell maturation through the TLR4/NF-κB pathway is highly immunogenic

Introduction

Human adenovirus type 7 (HAdv-7) infection is the main cause of upper respiratory tract infection, bronchitis and pneumonia in children. At present, there are no anti- adenovirus drugs or preventive vaccines in the market. Therefore, it is necessary to develop a safe and effective anti-adenovirus type 7 vaccine.

Methods

In this study, In this study, we used the baculovirus-insect cell expression system to design a recombinant subunit vaccine expressing adenovirus type 7 hexon protein (rBV-hexon) to induce high-level humoral and cellular immune responses. To evaluate the effectiveness of the vaccine, we first detected the expression of molecular markers on the surface of antigen presenting cells and the secretion of proinflammatory cytokines in vitro. We then measured the levels of neutralizing antibodies and T cell activation in vivo.

Results

The results showed that the rBV-hexon recombinant subunit vaccine could promote DC maturation and improve its antigen uptake capability, including the TLR4/NF-κB pathway which upregulated the expression of MHCI, CD80, CD86 and cytokines. The vaccine also triggered a strong neutralizing antibody and cellular immune response, and activated T lymphocytes.

Discussion

Therefore, the recombinant subunit vaccine rBV-hexon promoted promotes humoral and cellular immune responses, thereby has the potential to become a vaccine against HAdv-7.

Recombinantly Expressed Chimeric Fibers Demonstrate Discrete Type-Specific Neutralizing Epitopes in the Fowl Aviadenovirus E (FAdV-E) Fiber, Promoting the Optimization of FAdV Fiber Subunit Vaccines towards Cross-Protection in vivo

Vaccines against inclusion body hepatitis in chickens are complicated by the involvement of antigenically diverse fowl adenovirus types. Though immunization with fiber protein confers robust protection, type specificity of fiber antibodies is an obstacle for the desired broad coverage. In this study, we utilized information on multiple linear epitopes predicted in the Fowl Aviadenovirus E (FAdV-E) fiber head (knob) to develop chimeric fibers with an exchange between two serotypes’ sequences, each containing proposed epitopes. Two consecutive segments pertaining to amino acid positions 1 to 441 and 442 to 525/523 in the fibers of FAdV-8a and -8b, types of Fowl Aviadenovirus E that cause inclusion body hepatitis, were swapped reciprocally to result in novel chimeras, crecFib-8a/8b and crecFib-8b/8a. crecFib was indistinguishable from monospecific recombinant fibers in its eactivity with different FAdV antisera in Western blotting. However, contrary to the results for monospecific fibers, crecFib induced cross-neutralizing antibodies against both serotypes in chickens. This demonstrates three nonidentical epitopes in the FAdV-E fiber, the conserved epitope detected in Western blotting and at least two epitopes participating in neutralization, being type specific and located opposite residue position 441-442. Furthermore, we supply conformational evidence for a site in the fiber knob with accessibility critical for neutralization. With such an extended neutralization spectrum compared to those of individual fibers, crecFib was anticipated to fulfill and even extend the mechanistic basis of fiber-mediated protection toward bivalent coverage. Accordingly, crecFib, administered as a single-antigen component, protected chickens simultaneously against challenge with FAdV-8a or -8b, demonstrated by up-to-complete resistance to clinical disease, prevention of target organ-related changes, and significant reduction of viral load.

IMPORTANCE The control of inclusion body hepatitis, a disease of economic importance for chicken production worldwide, is complicated by an etiology involving multiple divergent fowl adenovirus types. The fiber protein is principally efficacious in inducing neutralizing and protective antibodies in vaccinated chickens; however, it faces limitations due to its intrinsic type specificity for neutralization. In this study, based on an in silico-guided prediction of multiple epitopes in the fowl adenovirus fiber head’s loops, we designed chimeric proteins, swapping N- and C-distal fiber portions, each containing putative epitopes, between divergent types FAdV-8a and -8b. In in vitro and in vivo studies, the chimeric fiber displayed extended properties compared to those of individual monotype-specific fibers, allowing the number, distribution, functionality, and conformational bearings of epitopes of the fowl adenovirus fiber to be characterized in more detail. Importantly, the chimeric fiber induced cross-neutralizing antibodies and protective responses in chickens against infections by both serotypes, promoting the advancement of broadly protective subunit vaccination strategies against FAdV.

Non-human primate adenoviruses of the Human Adenovirus B species are potent and broadly-acting oncolytic vector candidates

The use of human adenoviruses (hAds) as oncolytic agents has demonstrated considerable potential. However, their efficacy in clinical studies is generally moderate and often varies between patients. This may, in part, be attributable to variable pre-existing neutralizing immunity in patients, which can impact the antitumor efficacy and lead to response heterogeneity. Our aim was to isolate new Ads for the development of oncolytic vectors with low prevalence of neutralizing immunity in the human population. To this end, we isolated a collection of new nonhuman primate (nhp) Ads from stool samples of four great ape species held captive. We elected 12 isolates comprising the broadest genetic variability for further characterization. For three new nhpAds, all classified as the human adenovirus B (HAdV-B) species, no neutralizing activity could be detected when exposed to a preparation of immunoglobulins isolated from a pool of >1,000 donors as a surrogate of population immunity. In addition, the nhpAds of the HAdV-B species showed enhanced oncolytic potency compared to nhpAds of the HAdV-C species as well as to human adenovirus type 5 (HAdV-C5) in vitro when tested in a panel of 29 human cancer cell lines. Next-generation sequencing of the viral genomes revealed higher sequence similarity between hAds and nhpAds of HAdV-B compared to HAdV-C, which might underlie the differences in oncolytic ability. As a proof-of-concept, the Rb-binding domain of the E1A protein of the gorilla-derived HAdV-B nhpAd-lumc007 was deleted, thereby creating a new oncolytic derivative, which demonstrated increased oncolytic potential compared to HAdV-C5. Collectively, our data demonstrate that nhpAds of the HAdV-B species can serve as an alternative for the development of potent oncolytic Ad vectors with limited pre-existing neutralizing immunity in humans.

Chimeric Ad5.F35 vector evades anti-adenovirus serotype 5 neutralization opposing GUCY2C-targeted antitumor immunity

BACKGROUND

Adenovirus serotype 5 (Ad5) is a commonly used viral vector for transient delivery of transgenes, primarily for vaccination against pathogen and tumor antigens. However, endemic infections with Ad5 produce virus-specific neutralizing antibodies (NAbs) that limit transgene delivery and constrain target-directed immunity following exposure to Ad5-based vaccines. Indeed, clinical trials have revealed the limitations that virus-specific NAbs impose on the efficacy of Ad5-based vaccines. In that context, the emerging focus on immunological approaches targeting cancer self-antigens or neoepitopes underscores the unmet therapeutic need for more efficacious vaccine vectors.

METHODS

Here, we evaluated the ability of a chimeric adenoviral vector (Ad5.F35) derived from the capsid of Ad5 and fiber of the rare adenovirus serotype 35 (Ad35) to induce immune responses to the tumor-associated antigen guanylyl cyclase C (GUCY2C).

RESULTS

In the absence of pre-existing immunity to Ad5, GUCY2C-specific T-cell responses and antitumor efficacy induced by Ad5.F35 were comparable to Ad5 in a mouse model of metastatic colorectal cancer. Furthermore, like Ad5, Ad5.F35 vector expressing GUCY2C was safe and produced no toxicity in tissues with, or without, GUCY2C expression. Importantly, this chimeric vector resisted neutralization in Ad5-immunized mice and by sera collected from patients with colorectal cancer naturally exposed to Ad5.

CONCLUSIONS

These data suggest that Ad5.F35-based vaccines targeting GUCY2C, or other tumor or pathogen antigens, may produce clinically relevant immune responses in more (≥90%) patients compared with Ad5-based vaccines (~50%).

Nonreplicating Adenoviral Vectors: Improving Tropism and Delivery of Cancer Gene Therapy

Recent preclinical and clinical studies have used viral vectors in gene therapy research, especially nonreplicating adenovirus encoding strategic therapeutic genes for cancer treatment. Adenoviruses were the first DNA viruses to go into therapeutic development, mainly due to well-known biological features: stability in vivo, ease of manufacture, and efficient gene delivery to dividing and nondividing cells. However, there are some limitations for gene therapy using adenoviral vectors, such as nonspecific transduction of normal cells and liver sequestration and neutralization by antibodies, especially when administered systemically. On the other hand, adenoviral vectors are amenable to strategies for the modification of their biological structures, including genetic manipulation of viral proteins, pseudotyping, and conjugation with polymers or biological membranes. Such modifications provide greater specificity to the target cell and better safety in systemic administration; thus, a reduction of antiviral host responses would favor the use of adenoviral vectors in cancer immunotherapy. In this review, we describe the structural and molecular features of nonreplicating adenoviral vectors, the current limitations to their use, and strategies to modify adenoviral tropism, highlighting the approaches that may allow for the systemic administration of gene therapy.

Oral Immunization of Recombinant Lactococcus lactis and Enterococcus faecalis Expressing Dendritic Cell Targeting Peptide and Hexon Protein of Fowl Adenovirus 4 Induces Protective Immunity Against Homologous Infection

Hepatitis-hydropericardium syndrome (HPS) causes severe economic losses in the global poultry industry. The present study aims to explore oral immunization of recombinant Lactococcus lactis and Enterococcus faecalis expressing Hexon protein of fowl adenovirus 4 (FAdV-4). The bacteria L. lactis NZ9000 and E. faecalis MDXEF-1 were, respectively, modified as host strain to deliver truncated Hexon protein (ΔHexon) or ΔHexon protein fusing with dendritic cell (DC) targeting peptide (DC-ΔHexon) on the surface of bacteria. The expression of target protein in L. lactis NZ9000 and E. faecalis MDXEF-1 were detected by western blot. To evaluate the immune responses and protective efficacies provided by the live recombinant bacteria, chickens were immunized with the constructed ΔHexon-expressing bacteria three times at 2-week intervals, then experimentally challenged with hypervirulent FAdV-4/GX01. The results showed that oral immunizations with the four ΔHexon-expressing bacteria (NZ9000/ΔHexon-CWA, NZ9000/DC-ΔHexon-CWA, MDXEF-1/ΔHexon-CWA, and MDXEF-1/DC-ΔHexon-CWA), especially the two bacteria carrying DC-targeting peptide, stimulated higher levels of ΔHexon-specific sera IgG and secretory IgA (sIgA) in jejunal lavage fluid, higher proliferation of peripheral blood lymphocytes (PBLs) and higher levels of Th1/Th2-type cytokines, along with significantly decreased virus loads in liver and more offered protective efficacies against FAdV infection compared with PBS and empty vector control groups (p < 0.01). For chickens in the group MDXEF-1/DC-ΔHexon-CWA, the levels of aspartate transaminase (AST), alanine transaminase (ALT) and lactate dehydrogenase (LDH) in sera, and the virus loads in livers were significantly decreased vs. the other three ΔHexon-expressing bacteria (p < 0.01). The pathological changes in the hearts, livers, spleens and kidneys of chickens in MDXEF-1/DC-ΔHexon-CWA group were relatively slight compared to infection control group and other three ΔHexon-expressing bacteria groups. The rate of protection in MDXEF-1/DC-ΔHexon-CWA group was 90%. The present work demonstrated that cell surface-displayed target protein and immune enhancers in L. lactis and E. faecalis might be a promising approach to enhance immunity and immune efficacy against pathogen FAdV-4 infection.

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.

A novel human monoclonal antibody potently neutralizes human adenovirus serotype 7 by primarily targeting the adenovirus hexon protein

Human adenovirus serotype 7 (HAdV-7), belonging to species B, has caused severe lower respiratory tract diseases and even deaths recently. However, no adenovirus vaccine or therapeutic is available thus far. In this study, a HAdV-7-specific human monoclonal antibody (HMAb), 3-3E, isolated from single plasma cells obtained from the peripheral blood mononuclear cells of HAdV-7-infected patients showed potent HAdV-7 neutralization activity. The results showed HMAb 3-3E only binds to the hexon protein of intact HAdV-7 or the recombinant hexon protein and it does not bind to other intact virion particles. This could mean the antibody recognizes a conformational epitope of the hexon protein. Further, HMAb 3-3E potently neutralized HAdV-7 in vitro at low concentrations. In vivo studies showed HMAb 3-3E protected from HAdV-7 infection in a murine model. Therefore, HMAb 3-3E is promising as a safe and effective prophylactic and therapeutic treatment for HAdV-7 infection.

A Murine Monoclonal Antibody With Potent Neutralization Ability Against Human Adenovirus 7

B1-type human adenoviruses (HAdVs) HAdV-3, HAdV-7, and HAdV-55 have caused epidemics in North America, Asia, and Europe. However, to date, no adenovirus vaccines or antiviral drugs have been approved for general use. In the present work, a scFv-phage immune library was constructed and mouse monoclonal antibody (MMAb) 10G12 was obtained through selection. 10G12 is specific for HAdV-7 and binds the hexon loop1 and loop2 (LP12), resulting in strong neutralization activity against HAdV-7. Additionally, it is stable in serum and buffer at various pH values. The findings provide insight into adenovirus and antibody responses and may facilitate the design and development of adenovirus vaccines and antiviral drugs.

Molecular evolution of human adenovirus type 16 through multiple recombination events

Human mastadenoviruses (HAdVs) are non-enveloped, double-stranded DNA viruses that are comprised of more than 85 types classified within seven species (A-G) based on genomics. All HAdV prototypes and many newly defined type genomes have been completely sequenced and are available. Computational analyses of the prototypes and newly emergent HAdV strains provide insights into the evolutionary history and molecular adaptation of HAdV. Most types of HAdV-B are important pathogens causing severe respiratory infections or urinary tract infections and are well characterized. However, HAdV-16 of the B1 subspecies has rarely been reported and its genome is poorly characterized. In this study, bioinformatics analysis, based on genome sequences obtained in GenBank, suggested that HAdV-16, a prototype HAdV-B species, evolved from multiple intertypic recombination events. HAdV-16 genome contains the hexon loop 1 to loop 2 region from HAdV-E4, the partial hexon conserved region 4 (C4) from the subspecies HAdV-B2, genome region 30,897-33,384 containing the fiber gene from SAdV-35, and other genomic parts from the subspecies HAdV-B1. Moreover, analysis of sequence similarity with HAdV-E4 LI, LII, and SAdV-36 strains demonstrated the recombination events happened rather early. Further, amino acid sequence alignment indicated that the amino acid variations occurred in hypervariable regions (HVRs). Especially, the major difference in HVR7, which contains the critical neutralization epitope of HAdV-E4, between HAdV-16 and HAdV-E4 might explain the low level of cross-neutralization between these strains. Our findings promote better understanding on HAdV evolution, predicting newly emergent HAdV strains, and developing novel HAdV vectors.

Requirement of Cellular Protein CCT7 for the Replication of Fowl Adenovirus Serotype 4 (FAdV-4) in Leghorn Male Hepatocellular Cells Via Interaction with the Viral Hexon Protein

Fowl adenovirus serotype 4 (FAdV-4) causes hepatitis-hydropericardium syndrome (HHS), leading to severe economic losses in the poultry industry. Although the pathogenesis of FAdV-4 infection has caused much attention, the underlying molecular mechanisms remain poorly understood. Here, we identified chaperonin containing TCP-1 subunit eta (CCT7) as an interacting partner of the FAdV-4 capsid protein hexon. We found that ectopic expression of CCT7 in leghorn male hepatocellular (LMH) cells enhanced hexon expression in pRK5-flag-hexon transfected cells. On the contrary, knockdown of cellular CCT7 by RNAi markedly reduced hexon expression in FAdV-4-infected cells and suppressed viral replication. These data suggest that CCT7 is required for FAdV-4 replication and may serve as a potential target for controlling FAdV-4 infection.

Broadly neutralizing monoclonal antibodies against human adenovirus types 55, 14p, 7, and 11 generated with recombinant type 11 fiber knob

The re-emerging human adenovirus types HAdV7, HAdV14, and HAdV55 of species B have caused severe lower respiratory tract diseases and even deaths during recent outbreaks. However, no adenovirus vaccine or therapeutic has been approved for general use. These adenoviruses attach to host cells via the knob domain of the fiber, using human desmoglein 2 as the primary cellular receptor. In this study, a recombinant HAdV11 fiber knob trimer (HAdV11FK) expressed in E. coli was shown to induce broadly neutralizing antibodies against HAdV11, -7, -14p1, and -55 in mice. Using HAdV11FK as an antigen, three monoclonal antibodies, 6A7, 3F11, and 3D8, with high neutralizing activity were generated. More importantly, the results of in vitro neutralization assays demonstrated that 3F11 and 3D8 cross-neutralized HAdV11, -7, and -55, but not HAdV14p1. The amino acids 251KE252 within the F-G loop may be the crucial amino acids in the conformational epitope recognized by 3F11, which is common to HAdV11, -7, -14p, and -55, but is not present in HAdV14p1 and HAdV3. A two-amino-acid deletion in the HAdV14p1 structure breaks the short alpha helix (248SREKE252) that is present in the HAdV7, -11, -55, and -14p fiber knob structures. Our findings add to the knowledge of adenovirus fiber structure and antibody responses and are important for the design of adenovirus vaccines and antiviral drugs with broad activity.

Prevalence of Common Respiratory Viral Infections and Identification of Adenovirus in Hospitalized Adults in Harbin, China 2014 to 2017

Background: Respiratory infections pose a great challenge in global health, and the prevalence of viral infection in adult patients has been poorly understood in northeast China. Harbin is one of the major cities in northeast China, and more than half of any given year in Harbin is occupied by winter. To reveal the viral etiology and seasonality in adult patients from Harbin, a 4-year consecutive survey was conducted in Harbin, China.

Methods: From January 2014 to December 2017, specimens were obtained from adult patients admitted to the Second Affiliated Hospital of Harbin Medical University with lower respiratory tract infections. Sputum samples were examined by direct immunofluorescence assays to detect seven common respiratory viruses, including influenza virus (type A and B), parainfluenza virus (type 1 to 3), respiratory syncytial virus and adenovirus. Adenovirus positive samples were seeded onto A549 cells to isolate viral strains. Phylogenetic analysis was conducted on the highly variable region of adenoviral hexon gene.

Results: A total of 1,300 hospitalized adult patients with lower respiratory tract infections were enrolled, in which 189 patients (14.5%) were detected as having at least one viral infection. The co-infection rate in this study was 25.9% (49/189). The dominant viral pathogen from 2014 to 2017 was parainfluenza virus, with a detection rate of 7.2%, followed by influenza virus, respiratory syncytial virus and adenovirus. Based on the climate seasons determined by daily average temperature, the highest overall viral detection rate was detected in spring (22.0%, 52/236), followed by winter (13.4%, 109/813), autumn (11.4%, 13/114) and summer (10.9%, 15/137). Adenovirus type 3 strains with slight variations were isolated from positive cases, which were closely related to the GB strain from the United States, as well as the Harbin04B strain isolated locally.

Conclusion: This study demonstrated that common respiratory viruses were partially responsible for hospitalized lower respiratory tract infections in adult patients from Harbin, China, with parainfluenza virus as the dominant viral pathogen. Climate seasons could be rational indicators for the seasonality analysis of airborne viral infections. Future surveillance on viral mutations would be necessary to reveal the evolutionary history of respiratory viruses.

A Dendritic Cell-Targeted Adenoviral Vector Facilitates Adaptive Immune Response Against Human Glioma Antigen (CMV-IE) and Prolongs Survival in a Human Glioma Tumor Model

Antitumor immunotherapeutic strategies represent an especially promising set of approaches with rapid translational potential considering the dismal clinical context of high-grade gliomas. Dendritic cells (DCs) are the body's most professional antigen-presenting cells, able to recruit and activate T cells to stimulate an adaptive immune response. In this regard, specific loading of tumor-specific antigen onto dendritic cells potentially represents one of the most advanced strategies to achieve effective antitumor immunization. In this study, we developed a DC-specific adenoviral (Ad) vector, named Ad5scFvDEC205FF, targeting the DC surface receptor, DEC205. In vitro analysis shows that 60% of DCs was infected by this vector while the infectivity of other control adenoviral vectors was less than 10%, demonstrating superior infectivity on DCs. Moreover, an average of 14% of DCs were infected by Ad5scFvDEC205FF-GFP, while less than 3% of non-DCs were infected following in vivo administration, demonstrating highly selective in vivo DC infection. Importantly, vaccination with this vehicle expressing human glioma-specific antigen, Ad5scFvDEC205FF-CMV-IE, shows a prolonged survival benefit in GL261CMV-IE-implanted murine glioma models (p < 0.0007). Furthermore, when rechallenged, cancerous cells were completely rejected. In conclusion, our novel, viral-mediated, DC-based immunization approach has the significant therapeutic potential for patients with high-grade gliomas.

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.

Vaccine development for human mastadenovirus

Human mastadenovirus (HAdVs) can cause a broad spectrum of diseases in both children and adults, including acute respiratory infection, gastroenteritis, epidemic keratoconjunctivitis. Populations susceptible to adenovirus infection include children, immunocompromised patients and military recruits. To date, seven species (A-G) including more than 79 genotypes have been characterized, of which HAdV-B3, B4, B7 and the recently reemerged types 14 and 55 often lead to severe pneumonia. The live oral enteric-coated adenovirus type 4 and 7 vaccine, which was approved for use in US military personnel of 17 through 50 years of age, had been shown to be safe and highly effective in numerous clinical trials and by ongoing surveillance of febrile respiratory illness. However, there is currently no vaccine approved for general use in children and adults in any part of the world. This review article will summarize the epidemiological data available for adenovirus and the effectiveness of the adenovirus vaccine in the US military. It will also provide a brief overview of innovative vaccine strategies, animal models for vaccine evaluation, and issues regarding vaccine production.

Antitumor-specific T-cell responses induced by oncolytic adenovirus ONCOS-102 (AdV5/3-D24-GM-CSF) in peritoneal mesothelioma mouse model

Oncolytic adenoviral immunotherapy activates the innate immune system with subsequent induction of adaptive tumor‐specific immune responses to fight cancer. Hence, oncolytic viruses do not only eradicate cancer cells by direct lysis, but also generate antitumor immune response, allowing for long‐lasting cancer control and tumor reduction. Their therapeutic effect can be further enhanced by arming the oncolytic adenovirus with costimulatory transgenes and/or coadministration with other antitumor therapies. ONCOS‐102 has already been found to be well tolerated and efficacious against some types of treatment‐refractory tumors, including mesothelin‐positive ovarian cancer (NCT01598129). It induced local and systemic CD8+ T‐cell immunity and upregulated programmed death ligand 1. These results strongly advocate the use of ONCOS‐102 in combination with other therapeutic strategies in advanced and refractory tumors, especially those expressing the mesothelin antigen. The in vivo work presented herein describes the ability of the oncolytic adenovirus ONCOS‐102 to induce mesothelin‐specific T‐cells after the administration of the virus in bagg albino (BALB/c) mice with mesothelin‐positive tumors. We also demonstrate the effectiveness of the interferon‐γ the enzyme‐linked immunospot (ELISPOT) assay to detect the induction of T‐cells recognizing mesothelin, hexon, and E1A antigens in ONCOS‐102‐treated mesothelioma‐bearing BALB/c mice. Thus, the ELISPOT assay could be useful to monitor the progress of therapy with ONCOS‐102.

A tetravalent vaccine comprising hexon-chimeric adenoviruses elicits balanced protective immunity against human adenovirus types 3, 7, 14 and 55

Human adenovirus (Ad) species B contains several of the most important types associated with acute respiratory diseases, Ad3, -7, -14 and -55, which often lead to severe lower respiratory tract diseases and epidemic outbreaks. However, there is currently no Ad vaccine approved for general use. The major capsid protein, hexon, is the primary determinant recognized by neutralizing antibodies (NAbs). In this study, four recombinant Ads that have the same genome sequence as Ad3 with the exception of the hexon genes, rAd3EGFP, rAd3H7, rAd3H14 and rAd3H55, were combined as a tetravalent Ad candidate vaccine against Ad3, -7, -14 and -55. The replication efficiencies of chimeric rAd3H14, rAd3H7 and rAd3H55 were similar to that of rAd3EGFP. Recombinant rAd3EGFP, rAd3H7, rAd3H14 and rAd3H55 induced high titers of NAbs against Ad3, -7, -14 and -55, respectively, which were comparable to those induced by wild-type Ads. The mixture of the four recombinant Ads in equal proportions, rAdMix, or rAdMix inactivated by β-propiolactone, induced balanced NAb responses against Ad3, -7, -14 and -55 in mice without reciprocal immunological interference. In co-culture the four recombinant Ads replicated with a similar efficiency without reciprocal inhibition, and the progeny virions may be chimeric. Purified co-culture, rAdMix-C, also elicited balanced immune responses, suggesting a simple method for multivalent vaccine production. These results indicate the possible advantage of the four Ads as a live combined vaccine. Importantly, pre-immunization with rAdMix conferred protection against Ad3, -7, -14 or -55 challenge in mice in vivo. Thus, this research provides a novel tetravalent Ad vaccine candidate against Ad3, -7, -14 and -55.

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.

A novel capsid-modified oncolytic recombinant adenovirus type 5 for tumor-targeting gene therapy by intravenous route

Oncolytic adenovirus (Ad)-vectored gene therapy is a promising strategy for cancer treatment. However, the lack of cancer cell selectivity or tumor tissue specificity of Ads limits their clinical application by intravenous (IV) injection. In this paper, a novel recombinant Ad5 vector was constructed carrying the capsid protein IX modified by the tumor necrosis factor related apoptosis-inducing ligand (TRAIL), which targets tumor cells bearing high levels of its receptor far above those of normal cells. Specific association of the Ad virion with TRAIL was achieved using synthetic leucine zipper-like dimerization domains (zippers). Analysis of the chemical properties of the modified recombinant Ad (rAd5pz-zTRAIL-RFP) showed that the TRAIL protein was present on the surface of purified virus particles, and it could induce apoptosis of infected cancer cells prior to expression of foreign genes. We also constructed a novel modified recombinant oncolytic Ad (rAd5pz-zTRAIL-RFP-SΔ24E1a) which showed significantly enhanced anti-tumor effects both in vitro and in vivo by linkage of TRAIL to the viral capsid. Moreover, rAd5pz-zTRAIL-RFP-SΔ24E1a showed significantly improved tumor tissue targeting and reduced liver tropism when IV injected in vivo. Thus, we successfully obtained new oncolytic Ad5 gene therapy vectors with enhanced targeting and efficacy, providing a platform for further clinical application of Ad vectors for cancer treatment.

Identification of a Critical and Conformational Neutralizing Epitope in Human Adenovirus Type 4 Hexon

Human adenovirus type 4 (HAdV-4) is an epidemic virus that contributes to serious acute respiratory disease (ARD) in both pediatric and adult patients. However, no licensed drug or vaccine is currently available to the civilian population. The identification of neutralizing epitopes of HAdV-4 should allow the development of a novel antiviral vaccine and a novel gene transfer vector, and an effective neutralizing monoclonal antibody (MAb) will be useful in developing appropriate antiviral drugs. In this study, we report that MAb MN4b shows strong neutralizing activity against HAdV-4. MN4b recognizes a conformational epitope (418AGSEK422) within hypervariable region 7 (HVR7). Mutations within this site permitted HAdV-4 mutants to escape neutralization by MN4b and to resist neutralization by animal and human anti-HAdV-4 sera. A recombinant virus, rAd3-A4R7-1, containing the identified neutralizing epitope in the HVR7 region of HAdV-3 hexon, successfully induced antiserum that inhibited HAdV-4 infection. These results indicate that a small surface loop of HAdV-4 hexon is a critical neutralization epitope for this virus. The generation of MN4b and the identification of this neutralizing epitope may be useful in developing therapeutic treatment, a subunit vaccine, and a novel vector that can escape preexisting neutralization for HAdV-4.

IMPORTANCE Neutralizing antibodies are considered good tools for the prevention of human adenovirus type 4 (HAdV-4) infections. The identification of the epitopes recognized by such neutralizing antibodies is important for the generation of recombinant antiviral vaccines. However, until now, no neutralizing epitope has been reported for HAdV-4. Here, we developed a serotype-specific neutralizing MAb directed against HAdV-4, MN4b. We provide evidence that MN4b recognizes a conformational epitope within HVR7 of HAdV-4 hexon. Antisera generated to this conformational epitope displayed on HAdV-3 hexon inhibited infection of AD293 cells by HAdV-4. Our findings are very important for the development of therapeutic treatment, a subunit vaccine, and a novel vector for HAdV-4.

Immune protection efficacy of FAdV-4 surface proteins fiber-1, fiber-2, hexon and penton base

The spread of hydropericardium syndrome has recently become serious in China since 2015. There is, therefore, an urgent need for new, safe and effective vaccines that prevent the disease. Here, the immune protection induced by Escherichia coli-expressed capsid proteins of fowl adenovirus serotype 4, including fiber-1, fiber-2, penton base and hexon (loop-1 region) were compared in chickens at different inoculation amounts. According to challenge mortalities and tissue gross/micro lesion results, fiber-2 induced the best protection, followed by fiber-1 and hexon. Fiber-1 and fiber-2 provided complete protection against 10^5.5 TCID₅₀ viral load challenge with 100 or 50μg doses per chicken, respectively. Penton could induce effective protection only at the high dosage of 200μg per chicken. The immunoprotective characteristics of these FAdV-4 capsid proteins may prove useful for developing subunit vaccines to control hydropericardium syndrome.

Hitting the nail on the head: combining oncolytic adenovirus-mediated virotherapy and immunomodulation for the treatment of glioma

Glioblastoma is a highly aggressive malignant brain tumor with a poor prognosis and the median survival 14.6 months. Immunomodulatory proteins and oncolytic viruses represent two treatment approaches that have recently been developed for patients with glioblastoma that could extend patient survival and result in better treatment outcomes for patients with this disease. Together, these approaches could potentially augment the treatment efficacy and strength of these anti-tumor therapies. In addition to oncolytic activities, this combinatory approach introduces immunomodulation locally only where cancerous cells are present. This thereby results in the change of the tumor microenvironment from immune-suppressive to immune-vulnerable via activation of cytotoxic T cells or through the removal of glioma cells immune-suppressive capability. This review discusses the strengths and weaknesses of adenoviral oncolytic therapy, and highlights the genetic modifications that result in more effective and targeted viral agents. Additionally, the mechanism of action of immune-activating agents is described and the results of previous clinical trials utilizing these treatments in other solid tumors are reviewed. The feasibility, synergy, and limitations for treatments that combine these two approaches are outlined and areas for which more work is needed are considered.

Seroprevalence of neutralizing antibodies against adenovirus type 14 and 55 in healthy adults in Southern China

Re-emerging human adenovirus types 14 (Ad14) and 55 (Ad55) have caused severe respiratory diseases and even deaths during recent outbreaks. However, the seroprevalence of neutralizing antibodies (nAbs) in healthy adults, which may reflect previous circulation and help to predict potential outbreaks, remains unclear. In this study, we established micro-neutralizing (MN) assays on the basis of recombinant Ad14 and Ad55 reporter viruses, and we investigated serum nAbs in healthy blood donors from Southern China. We found that the overall seropositive rates were 24.8% and 22.4% for Ad14 and Ad55 nAbs, respectively. The seropositive rates were low in individuals younger than 20, and they gradually increased with age. Ad55-seropositive individuals tended to have high nAb titers (>1000), while low (72–200) and moderate (201–1000) nAb levels were frequently observed in Ad14-seropositive ones. Surprisingly, the seropositive rates and nAb levels were associated with the blood type but not the gender of the blood donors, with type AB individuals displaying higher seropositive rates and nAb levels. Interestingly, a significant positive correlation was observed between Ad14 and Ad55 seroprevalence, and higher titers of nAbs were detected in double-positive individuals compared to single-positive ones. These results clarified the human humoral immune responses against Ad14 and Ad55 and revealed a low level of herd immunity in some subpopulations, which emphasized the importance of monitoring these two highly virulent adenoviruses and reinforced the development of prophylactic vaccines.

Engineered adenovirus fiber shaft fusion homotrimer of soluble TRAIL with enhanced stability and antitumor activity

Successful cancer therapies aim to induce selective apoptosis in neoplastic cells. Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) is considered an attractive anticancer agent due to its tumor cell-specific cytotoxicity. However, earlier studies with recombinant TRAIL revealed many shortcomings, including a short half-life, off-target toxicity and existence of TRAIL-resistant tumor cells. In this study, we developed a novel engineering strategy for recombinant soluble TRAIL by redesigning its structure with the adenovirus knobless fiber motif to form a stable homotrimer with improved antitumor activity. The result is a highly stable fiber-TRAIL fusion protein that could form homotrimers similar to natural TRAIL. The recombinant fusion TRAIL developed here displayed high specific activity in both cell-based assays in vitro and animal tests in vivo. This construct will serve as a foundation for a new generation of recombinant proteins suitable for use in preclinical and clinical studies and for effective combination therapies to overcome tumor resistance to TRAIL.

Human Adenovirus Serotype 3 Vector Packaged by a Rare Serotype 14 Hexon

Recombinant adenovirus serotype 3 (rAd3), which infects cells through the receptor desmoglein 2 (DSG2), has been investigated as a vector for gene therapy or vaccination. However, pre-existing anti-vector immunity may limit the practical application of rAd3. In this study, we investigated the seroprevalence and neutralizing antibody (NAb) titers to Ad3 and alternate serotypes in normal healthy adults in southern China. Sera samples had a high seroprevalence (80.00%) against Ad3 and Ad7 (85.83%), compared with Ad14 (22.50%). Furthermore, 19.17% and 25.83% of samples had high-titer neutralizing antibodies to Ad3 and Ad7, respectively, compared with 3.33% against Ad14. We constructed a chimeric adenovirus, rAd3H14, designed to evade anti-vector immunity by replacing the enhanced green fluorescent protein (EGFP)-expressing hexon of the rAd3EGFP vector with a hexon from Ad14. The chimeric vector rAd3H14 was not neutralized in vitro efficiently by Ad3 NAbs using sera from mice and normal healthy human volunteers. Furthermore, in contrast to the unmodified vector rAd3EGFP, rAd3H14 induced robust antibody responses against EGFP in mice with high levels of pre-existing anti-Ad3 immunity. In conclusion, the chimeric vector rAd3H14 may be a useful alternative vector in adult populations with a high prevalence of Ad3 NAbs.

Localization of neutralization epitopes on adenovirus fiber knob from species C

Although potential neutralization epitopes on the fiber knob of adenovirus (AdV) serotype 2 (Ad2) and Ad5 have been revealed, few studies have been carried out to identify neutralization epitopes on the knob from a broader panel of AdV serotypes. In this study, based on sequence and structural analysis of knobs from Ad1, Ad2, Ad5 and Ad6 (all from species C), several trimeric chimeric knob proteins were expressed in Escherichia coli to identify the locations of neutralization epitopes on the knobs by analysing their reactivity with mouse and rabbit polyclonal sera raised against AdVs and human sera with natural AdV infection. The dominant neutralization epitopes were located mainly in the N-terminal part of knobs from Ad1, Ad2 and Ad5, but they seemed to be located in the C-terminal part of the Ad6 knob, with some individual differences in rabbit and human populations. Our study adds to our understanding of humoral immune responses to AdVs and will facilitate the construction of more desirable capsid-modified recombinant Ad5 vectors.

Cytotoxic T lymphocyte antigen 4 decreases humoral and cellular immunity by adenovirus to enhance target GFP gene transfer in C57BL/6 mice

Adenoviruses (Ad) are once potential and promising vectors for gene delivery, but the immunogenicity attenuates its transfer efficiency. Cytotoxic T lymphocyte antigen 4 (CTLA-4) can inhibit T cell immunity. Thus, we aimed to study the effect of CTLA-4 in the process of Ad-mediated gene transfer. The C57BL/6 mice were injected by Ad vectors at twice, and CTLA-4 was administrated after the first Ad injection. Then, the CD3(+)CD4(+) T cells and circulating levels of IL-2, IL-4, and anti-Ad IgG were decreased by CTLA-4, while Ad generated immune responses. The green fluorescence protein (GFP) expressions of tissues were enhanced by CTLA-4 till injection of Ad at twice. Our results indicate that CTLA-4 can inhibit humoral and cellular immunity by adenovirus generation to enhance GFP delivery, and provide a potential way to assist in Ad-mediated gene transfer.

Identification and Application of Neutralizing Epitopes of Human Adenovirus Type 55 Hexon Protein

Human adenovirus type 55 (HAdV55) is a newly identified re-emergent acute respiratory disease (ARD) pathogen with a proposed recombination of hexon gene between HAdV11 and HAdV14 strains. The identification of the neutralizing epitopes is important for the surveillance and vaccine development against HAdV55 infection. In this study, four type-specific epitope peptides of HAdV55 hexon protein, A55R1 (residues 138 to 152), A55R2 (residues 179 to 187), A55R4 (residues 247 to 259) and A55R7 (residues 429 to 443), were predicted by multiple sequence alignment and homology modeling methods, and then confirmed with synthetic peptides by enzyme-linked immunosorbent assay (ELISA) and neutralization tests (NT). Finally, the A55R2 was incorporated into human adenoviruses 3 (HAdV3) and a chimeric adenovirus rAd3A55R2 was successfully obtained. The chimeric rAd3A55R2 could induce neutralizing antibodies against both HAdV3 and HAdV55. This current study will contribute to the development of novel adenovirus vaccine candidate and adenovirus structural analysis.

Mapping the epitope of neutralizing monoclonal antibodies against human adenovirus type 3

Human adenovirus type 3 (HAdV-3) has produced a global epidemic in recent years causing serious diseases such as pneumonia in both pediatric and adult patients. Development of an effective neutralizing monoclonal antibody (MAb) and identification of its neutralizing epitope is important for the control of HAdV-3 infection. In this study, three neutralizing MAbs were generated, of which MAb 3D7 had a high neutralization titer of 4096 (approximately 0.5 μg/ml) against HAdV-3 infection. In indirect enzyme-linked immunosorbent assays, all three MAbs specifically recognized HAdV-3 virus particles and hexon protein, but did not react with the virus particles or the hexon protein of HAdV-7. Analyses using a series of peptides and chimeric adenovirus particles of epitope mutants revealed that all three MAbs bound to the same exposed region (amino acid positions 244-254 of hexon) in hypervariable region 4 (HVR4), which is highly conserved among global HAdV-3 strains. The amino acids T246 and G250 may be the critical amino acids recognized by these MAbs. MAb 3D7 reduced the recombinant enhanced green fluorescent protein-expressing HAdV-3 (rAd3EGFP) load recovered in the lungs of mice at 3 days post-infection. The generation of MAb 3D7 and the identification of its neutralizing epitope may be useful for therapeutic treatment development, subunit vaccine construction, and virion structural analysis for HAdV-3.

Antigenic variability among two subtypes of human adenovirus serotype 7

Human adenovirus type 7 (HAdV-7) is one of the major serotypes responsible for acute respiratory infection. It is important to investigate the antigenic variabilities of different HAdV-7 genomic subtypes for vaccine development. Phylogenetic analysis of global HAdV-7 strains and major antigen proteins showed that HAdV-7 could be classified into two subtypes. There were three highly variable regions (HVR1, HVR4, and HVR7) in the hexon protein that varied between subtypes. Within each of the subtypes, these regions were conserved. Two subtype HAdV-7 strains isolated in China were used to immunize mice for antigenic characterization. Mice immunized with one subtype strain showed 4-8-fold lower neutralizing antibody titers against another subtype strain. ELISA results showed that the variation in HVR1, 4, and 7 regions contributed to antigenic change, and it may be concluded that the three regions contain subtype-specific epitopes. In summary, strains of HAdV-7 could be divided into two subtypes using genome sequence and antigenic analysis; our results could be important for HAdV-7 vaccine development.

Trimeric knob protein specifically distinguishes neutralizing antibodies to different human adenovirus species: potential application for adenovirus seroepidemiology

Adenoviruses (Ads) are non-enveloped DNA viruses that have been extensively studied and used as vectors for gene therapy and several potential vaccines. There are 57 Ad serotypes in seven species (A-G), and Ad neutralizing antibody (NAb) titres can vary by serotype and geographical location. Until now serotype- and species-specific antibodies have been detected by neutralization or haemagglutination inhibition assays. These expensive and cumbersome methods of adenovirus typing have mainly been used in epidemiological studies. Our prior work demonstrated that NAbs against the fiber protein are commonly generated during natural Ad infection in humans and the trimeric knob is preferentially recognized by fiber-induced NAbs. In this study, we expressed nine trimeric knob proteins from representative Ad serotypes of human Ad (HAdV)-A-F in Escherichia coli and found no cross-reactivity of these recombinant proteins with rabbit hyperimmune sera (among HAdV-A-F or within HAdV-C). Results of the ELISA based on Ad2 and Ad5 (both HAdV-C) knob proteins were consistent with those of neutralization assays, indicating that the trimeric knob protein would be a good candidate antigen for detecting Ad serotype-specific NAbs in sera from naturally infected subjects. We also demonstrated the primary seroepidemiology of nine Ad serotypes in 274 children using the knob-based ELISA. These results have potential implications for epidemiology of Ad serotypes and future development of Ad-based vaccines and gene therapy.

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.

Molecular and serological characterization of species B2 adenovirus strains isolated from children hospitalized with acute respiratory disease in Buenos Aires, Argentina

BACKGROUND

Between September 2000 and November 2005, approximately 10% of the retrospectively examined human adenovirus (HAdV)-positive pediatric cases of acute respiratory disease (ARD) requiring hospitalization at the Hospital Nacional de Pediatria Juan P. Garrahan in Buenos Aires, Argentina, were found to have a HAdV-B2 infection.

OBJECTIVE

To characterize genetically and antigenically the HAdV-B2 virus isolates.

STUDY DESIGN

Restriction enzyme analysis (REA), hexon and fiber gene sequencing and virus neutralization assays (VN) were carried out on 8 HAdV-B2 respiratory virus isolates.

RESULTS

REA showed that the 8 examined HAdV-B2 virus isolates were HAdV11, belonging to two genomic variants: HAdV11a and a BclI variant of HAdV11c which we designated 11c4. Molecular analysis of the hexon genes showed that both REA variants had a HAdV11-like hexon gene. Confirming previous reports, the 7 HAdV11a virus isolates were found to have HAdV14-like fiber genes and therefore are HAdV H11/F14. The fiber gene of the HAdV11c4 virus isolates most closely resembled that of various strains of HAdV7. In VN assays, the 4 tested HAdV11a strains were serotyped as HAdV11-14. The HAdV11c4 strain was serotyped as HAdV11 but also showed a weak but significant reactivity with antiserum to HAdV7. Compared with the other HAdV-positive cases in our study, infection with HAdV11 caused a similarly severe disease.

CONCLUSIONS

Our results provide evidence to the long term world-wide circulation of HAdV H11/F14 as a causative agent of ARD. Combined, our molecular and serology data support the rationale to base the molecular typing and designation of recombinant viruses on the sequences of the hexon and fiber genes.