The Adenovirus Dodecahedron: Beyond the Platonic Story

Integrin-Targeting Strategies for Adenovirus Gene Therapy

Numerous human adenovirus (AdV) types are endowed with arginine-glycine-aspartic acid (RGD) sequences that enable them to recognize vitronectin-binding (αv) integrins. These RGD-binding cell receptors mediate AdV entry into host cells, a crucial early step in virus infection. Integrin interactions with adenoviruses not only initiate receptor-mediated endocytosis but also facilitate AdV capsid disassembly, a prerequisite for membrane penetration by AdV protein VI. This review discusses fundamental aspects of AdV-host interactions mediated by integrins. Recent efforts to re-engineer AdV vectors and non-viral nanoparticles to target αv integrins for bioimaging and the eradication of cancer cells will also be discussed.

Redirect Tropism of Fowl Adenovirus 4 Vector by Modifying Fiber2 with Variable Domain of Heavy-Chain Antibody

The variable domain of a heavy-chain antibody (VHH) has the potential to be used to redirect the cell tropism of adenoviral vectors. Here, we attempted to establish platforms to simplify the screening of VHHs for their specific targeting function when being incorporated into the fiber of adenovirus. Both fowl adenovirus 4 (FAdV-4) and simian adenovirus 1 (SAdV-1) have two types of fiber, one of which is dispensable for virus propagation and is a proper site for VHH display. An intermediate plasmid, pMD-FAV4Fs, was constructed as the start plasmid for FAdV-4 fiber2 modification. Foldon from phage T4 fibritin, a trigger for trimerization, was employed to bridge the tail/shaft domain of fiber2 and VHHs against human CD16A, a key membrane marker of natural killer (NK) cells. Through one step of restriction-assembly, the modified fiber2 was transferred to the adenoviral plasmid, which was linearized and transfected to packaging cells. Five FAdV-4 viruses carrying the GFP gene were finally rescued and amplified, with three VHHs being displayed. One recombinant virus, FAdV4FC21-EG, could hardly transduce human 293 or Jurkat cells. In contrast, when it was used at a multiplicity of infection of 1000 viral particles per cell, the transduction efficiency reached 51% or 34% for 293 or Jurkat cells expressing exogenous CD16A. Such a strategy of fiber modification was transplanted to the SAdV-1 vector to construct SAdV1FC28H-EG, which moderately transduced primary human NK cells while the parental virus transduced none. Collectively, we reformed the strategy of integrating VHH to fiber and established novel platforms for screening VHHs to construct adenoviral vectors with a specific tropism.

The Biodistribution of Replication-Defective Simian Adenovirus 1 Vector in a Mouse Model

The administration route affects the biodistribution of a gene transfer vector and the expression of a transgene. A simian adenovirus 1 vector carrying firefly luciferase and GFP reporter genes (SAdV1-GFluc) were constructed, and its biodistribution was investigated in a mouse model by bioluminescence imaging and virus DNA tracking with real-time PCR. Luciferase activity and virus DNA were mainly found in the liver and spleen after the intravenous administration of SAdV1-GFluc. The results of flow cytometry illustrated that macrophages in the liver and spleen as well as hepatocytes were the target cells. Repeated inoculation was noneffective because of the stimulated serum neutralizing antibodies (NAbs) against SAdV-1. A transient, local expression of low-level luciferase was detected after intragastric administration, and the administration could be repeated without compromising the expression of the reporter gene. Intranasal administration led to a moderate, constant expression of a transgene in the whole respiratory tract and could be repeated one more time without a significant increase in the NAb titer. An immunohistochemistry assay showed that respiratory epithelial cells and macrophages in the lungs were transduced. High luciferase activity was restricted at the injection site and sustained for a week after intramuscular administration. A compromised transgene expression was observed after a repeated injection. When these mice were intramuscularly injected for a third time with the human adenovirus 5 (HAdV-5) vector carrying a luciferase gene, the luciferase activity recovered and reached the initial level, suggesting that the sequential use of SAdV-1 and HAdV-5 vectors was practicable. In short, the intranasal inoculation or intramuscular injection may be the preferred administration routes for the novel SAdV-1 vector in vaccine development.

African swine fever virus A137R assembles into a dodecahedron cage

African swine fever (ASF) is a highly contagious viral disease that affects domestic and wild pigs. The causative agent of ASF is African swine fever virus (ASFV), a large double-stranded DNA virus with a complex virion structure. Among the various proteins encoded by ASFV, A137R is a crucial structural protein associated with its virulence. However, the structure and molecular mechanisms underlying the functions of A137R remain largely unknown. In this study, we present the structure of A137R determined by cryogenic electron microscopy single-particle reconstruction, which reveals that A137R self-oligomerizes to form a dodecahedron-shaped cage composed of 60 polymers. The dodecahedron is literally equivalent to a T = 1 icosahedron where the icosahedral vertexes are located in the center of each dodecahedral facet. Within each facet, five A137R protomers are arranged in a head-to-tail orientation with a long N-terminal helix forming the edge through which adjacent facets stitch together to form the dodecahedral cage. Combining structural analysis and biochemical evidence, we demonstrate that the N-terminal domain of A137R is crucial and sufficient for mediating the assembly of the dodecahedron. These findings imply the role of A137R cage as a core component in the icosahedral ASFV virion and suggest a promising molecular scaffold for nanotechnology applications.

IMPORTANCE

African swine fever (ASF) is a lethal viral disease of pigs caused by African swine fever virus (ASFV). No commercial vaccines and antiviral treatments are available for the prevention and control of the disease. A137R is a structural protein of ASFV that is associated with its virulence. The discovery of the dodecahedron-shaped cage structure of A137R in this study is of great importance in understanding ASFV pathogenicity. This finding sheds light on the molecular mechanisms underlying the functions of A137R. Furthermore, the dodecahedral cage formed by A137R shows promise as a molecular scaffold for nanoparticle vectors. Overall, this study provides valuable insights into the structure and function of A137R, contributing to our understanding of ASFV and potentially opening up new avenues for the development of vaccines or treatments for ASF.

Engineering the ADDobody protein scaffold for generation of high-avidity ADDomer super-binders

Adenovirus-derived nanoparticles (ADDomer) comprise 60 copies of adenovirus penton base protein (PBP). ADDomer is thermostable, rendering the storage, transport, and deployment of ADDomer-based therapeutics independent of a cold chain. To expand the scope of ADDomers for new applications, we engineered ADDobodies, representing PBP crown domain, genetically separated from PBP multimerization domain. We inserted heterologous sequences into hyper-variable loops, resulting in monomeric, thermostable ADDobodies expressed at high yields in Escherichia coli. The X-ray structure of an ADDobody prototype validated our design. ADDobodies can be used in ribosome display experiments to select a specific binder against a target, with an enrichment factor of ∼104-fold per round. ADDobodies can be re-converted into ADDomers by genetically reconnecting the selected ADDobody with the PBP multimerization domain from a different species, giving rise to a multivalent nanoparticle, called Chimera, confirmed by a 2.2 Å electron cryo-microscopy structure. Chimera comprises 60 binding sites, resulting in ultra-high, picomolar avidity to the target.

Overcoming biological barriers by virus-like drug particles for drug delivery

Virus-like particles (VLPs) have natural structural antigens similar to those found in viruses, making them valuable in vaccine immunization. Furthermore, VLPs have demonstrated significant potential in drug delivery, and emerged as promising vectors for transporting chemical drug, genetic drug, peptide/protein, and even nanoparticle drug. With virus-like permeability and strong retention, they can effectively target specific organs, tissues or cells, facilitating efficient intracellular drug release. Further modifications allow VLPs to transfer across various physiological barriers, thus acting the purpose of efficient drug delivery and accurate therapy. This article provides an overview of VLPs, covering their structural classifications, deliverable drugs, potential physiological barriers in drug delivery, strategies for overcoming these barriers, and future prospects.

ADDovenom: Thermostable Protein-Based ADDomer Nanoparticles as New Therapeutics for Snakebite Envenoming

Snakebite envenoming can be a life-threatening medical emergency that requires prompt medical intervention to neutralise the effects of venom toxins. Each year up to 138,000 people die from snakebites and threefold more victims suffer life-altering disabilities. The current treatment of snakebite relies solely on antivenom-polyclonal antibodies isolated from the plasma of hyperimmunised animals-which is associated with numerous deficiencies. The ADDovenom project seeks to deliver a novel snakebite therapy, through the use of an innovative protein-based scaffold as a next-generation antivenom. The ADDomer is a megadalton-sized, thermostable synthetic nanoparticle derived from the adenovirus penton base protein; it has 60 high-avidity binding sites to neutralise venom toxins. Here, we outline our experimental strategies to achieve this goal using state-of-the-art protein engineering, expression technology and mass spectrometry, as well as in vitro and in vivo venom neutralisation assays. We anticipate that the approaches described here will produce antivenom with unparalleled efficacy, safety and affordability.

Selenadiazole Inhibited Adenovirus-Induced Apoptosis through the Oxidative-Damage-Mediated Bcl-2/Stat 3/NF-κB Signaling Pathway

Human adenovirus type 7 (HAdV7) infection causes severe pneumonia, yet there are still no breakthroughs in treatment options for adenovirus, and the road to antiviral drug development faces major challenges. We attempted to find new drugs and we stumbled upon one: selenadiazole. Selenadiazole has been shown to have significant anti-tumor effects due to its unique chemical structure and drug activity. However, its effectiveness against viruses has not been evaluated yet. In our study, selenadiazole also showed superior antiviral activity. In vitro experiments, selenadiazole was able to inhibit adenovirus-mediated mitochondrial-oxidative-damage-related apoptosis, and in in vivo experiments, selenadiazole was able to inhibit apoptosis by modulating the apoptotic signaling pathway Bcl-2/Stat3/NF-κB, etc., and was able to largely attenuate adenovirus-infection-induced pneumonia and lung injury in mice. This study aims to describe a new antiviral treatment option from the perspective of anti-adenovirus-mediated oxidative stress and its associated apoptosis and to provide theoretical guidance for the treatment of clinical adenovirus infection to a certain extent.

A recombinant virus-like particle vaccine against adenovirus-7 induces a potent humoral response

Adenoviruses (AdVs) cause infections in humans that range from mild to severe, and can cause outbreaks particularly in close contact settings. Several human AdV types have been identified, which can cause a wide array of clinical manifestations. AdV types 4 and 7 (AdV-4 and AdV-7), which are among the most commonly circulating types in the United States, are known to cause acute respiratory disease that can result in hospitalization and rarely, death. Currently, the only vaccines approved for use in humans are live virus vaccines against AdV-4 and AdV-7, though these vaccines are only authorized for use in U.S. military personnel. While they are efficacious, use of these live virus vaccines carries considerable risks of vaccine-associated viral shedding and recombination. Here, we present an alternative vaccination strategy against AdV-7 using the virus-like particle platform (AdVLP-7). We describe the production of stable recombinant AdVLP-7, and demonstrate that AdVLP-7 is structurally analogous to wild-type AdV-7 virions (WT AdV-7). Preclinical immunogenicity studies in mice show that AdVLP-7 elicits a potent humoral immune response, comparable to that observed in mice immunized with WT AdV-7. Specifically, AdVLP-7 induces high titers of antibodies against AdV-7-specific antigens that can effectively neutralize AdV-7.

In vitro generated antibodies guide thermostable ADDomer nanoparticle design for nasal vaccination and passive immunization against SARS-CoV-2

Background

Due to COVID-19, pandemic preparedness emerges as a key imperative, necessitating new approaches to accelerate development of reagents against infectious pathogens.

Methods

Here, we developed an integrated approach combining synthetic, computational and structural methods with in vitro antibody selection and in vivo immunization to design, produce and validate nature-inspired nanoparticle-based reagents against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2).

Results

Our approach resulted in two innovations: (i) a thermostable nasal vaccine called ADDoCoV, displaying multiple copies of a SARS-CoV-2 receptor binding motif derived epitope and (ii) a multivalent nanoparticle superbinder, called Gigabody, against SARS-CoV-2 including immune-evasive variants of concern (VOCs). In vitro generated neutralizing nanobodies and electron cryo-microscopy established authenticity and accessibility of epitopes displayed by ADDoCoV. Gigabody comprising multimerized nanobodies prevented SARS-CoV-2 virion attachment with picomolar EC50. Vaccinating mice resulted in antibodies cross-reacting with VOCs including Delta and Omicron.

Conclusion

Our study elucidates Adenovirus-derived dodecamer (ADDomer)-based nanoparticles for use in active and passive immunization and provides a blueprint for crafting reagents to combat respiratory viral infections.

Adenovirus-Derived Nano-Capsid Platforms for Targeted Delivery and Penetration of Macromolecules into Resistant and Metastatic Tumors

Macromolecular therapeutics such as nucleic acids, peptides, and proteins have the potential to overcome treatment barriers for cancer. For example, nucleic acid or peptide biologics may offer an alternative strategy for attacking otherwise undruggable therapeutic targets such as transcription factors and similar oncologic drivers. Delivery of biological therapeutics into tumor cells requires a robust system of cell penetration to access therapeutic targets within the cell interior. A highly effective means of accomplishing this may be borrowed from cell-penetrating pathogens such as viruses. In particular, the cell entry function of the adenovirus penton base capsid protein has been effective at penetrating tumor cells for the intracellular deposition of macromolecular therapies and membrane-impermeable drugs. Here, we provide an overview describing the evolution of tumor-targeted penton-base-derived nano-capsids as a framework for discussing the requirements for overcoming key barriers to macromolecular delivery. The development and pre-clinical testing of these proteins for therapeutic delivery has begun to also uncover the elusive mechanism underlying the membrane-penetrating function of the penton base. An understanding of this mechanism may unlock the potential for macromolecular therapeutics to be effectively delivered into cancer cells and to provide a treatment option for tumors resisting current clinical therapies.

The pathologic spectrum of adenovirus nephritis in the kidney allograft

Adenovirus nephritis (ADVN) is a rare and understudied complication of kidney transplantation. Unlike BK virus nephropathy (BKVN), our knowledge of clinicopathologic manifestations of ADVN remains rudimentary and essentially limited to case reports. To expand on this, we retrospectively studied 11 kidney transplant recipients with ADVN and compared their allograft biopsies to 33 kidney transplant recipients with BKVN using conventional microscopy and the 770 gene Nanostring Banff Human Organ Transplant Profiling Panel. Patients with ADVN had a median age of 44 years, were predominantly male, and developed ADVN at a median of 31 months post-transplantation. Eight patients presented with fever and ten had hematuria. The most common histologic manifestations included granulomas (82%), tubulocentric inflammation (73%), and tubular degenerative changes consistent with acute tubular necrosis (73%). During a median follow-up of 55 months after biopsy, three patients developed allograft failure from subsequent acute rejection. All seven patients with available follow-up PCR showed resolution of viremia at a median of 30 days after diagnosis. Compared to BKVN, ADVN demonstrated more granulomas and less tubulointerstitial scarring. On follow-up, patients with ADVN had more rapid clearance of viral DNA from plasma. Transcriptomic analyses showed that ADVN had increased expression of several pro-inflammatory transcriptomes, mainly related to innate immunity, was associated with increased expression of transcripts with inhibitory effects on inflammatory response and showed higher enrichment with neutrophils, which can cause aggressive but short-lasting damage. Thus, we demonstrate that, despite its association with aggressive neutrophil-rich inflammation, ADVN does not often lead to allograft failure. Hence, preventing subsequent acute rejection following resolution of ADVN may improve allograft survival.

First Evidence of Fowl Adenovirus Induced Inclusion Body Hepatitis in Chicken in Bangladesh

Background

The livestock sector contributes 1.90% to the GDP in Bangladesh during 2021-22. Poultry is one of the important subsectors struggling with diseases. Fowl adenoviruses (FAdVs) cause numerous diseases resulting in economic losses to the poultry industry worldwide. Several FAdV serotypes cause inclusion body hepatitis in chicken. Although FAdV infection was suspected, there was no confirmatory report from Bangladesh. The study was conducted to investigate the FAdV infection and antibodies in chicken.

Methods

A total of 50 samples, each composed of liver and spleen, were collected from different chickens of Gazipur, Dinajpur, and Panchagarh district. Each location belongs to A, B, and C poultry zones of Bangladesh, respectively. Viruses were detected by real-time PCR and conventional PCR. Blood samples (n = 303) were collected at the beginning and after the recovery from infection and tested by indirect ELISA. Sequencing of PCR products was done for serotyping and phylogenetic analysis.

Results

Clinical signs were observed including anorexia, drowsiness, ruffled feathers, reduced body weight, lack of uniformity, and high mortality (15-25%). Enlarged friable liver with yellow to tan color mottled with the focal soft area, fluid in pericardial sac, swollen and hemorrhagic kidneys, enlarged congested spleen and pancreas, etc. were found on postmortem examination. FAdVs were detected in 90% of the flocks except commercial layer flock from Dinajpur. Three serotypes, namely, 8b (70%), 11 (10%), and 5 (10%) were detected. Anti-FAdV antibody was detected in 80% flocks at the beginning of infection and in 90% of the flocks after recovery from infection. The antibody titer increases significantly (p < 0.05) after recovery from infection. Phylogenetic analysis revealed that the Bangladeshi FAdVs have close identity with viruses from Asia, Europe, and South and North America.

Conclusions

These findings suggested that several introductions of FAdVs were taken place in Bangladesh. To combat the disease, vaccination along with maintenance of biosecurity is essential.

Mastadenovirus Molecular Diversity in Waste and Environmental Waters from the Lisbon Metropolitan Area

In face of the absence of epidemiological data regarding the circulation of human adenoviruses (HAdV) in Portugal, this study aimed at the evaluation of their molecular diversity in waste and environmental waters in the Lisbon Metropolitan Area (LMA). Using samples collected between 2018 and 2021, the HAdV hexon protein-coding sequence was partially amplified using three nested touch-down PCR protocols. The amplification products obtained were analyzed in parallel by two approaches: molecular cloning followed by Sanger sequencing and Next-Generation Sequencing (NGS) using Illumina^® sequencing. The analysis of NGS-generated data allowed the identification of a higher diversity of HAdV-A (19%), -B (1%), -C (3%), -D (24%), and -F (25%) viral types, along with murine adenovirus (MAdV-2; 30%) in the wastewater treatment plant samples. On the other hand, HAdV-A (19%), -D (32%), and -F (36%) were identified in environmental samples, and possibly MAdV-2 (14%). These results demonstrate the presence of fecal contamination in environmental waters and the assessment of the diversity of this virus provides important information regarding the distribution of HAdV in LMA, including the detection of HAdV-F41, the most frequently reported in water worldwide.

Stimulation of the immune system by a tumor antigen-bearing adenovirus-inspired VLP allows control of melanoma growth

Virus-like particles (VLPs) are versatile protein-based platforms that can be used as a vaccine platform mainly in infectiology. In the present work, we compared a previously designed, non-infectious, adenovirus-inspired 60-mer dodecahedric VLP to display short epitopes or a large tumor model antigen. To validate these two kinds of platforms as a potential immuno-stimulating approach, we evaluated their ability to control melanoma B16-ovalbumin (OVA) growth in mice. A set of adjuvants was screened, showing that polyinosinic-polycytidylic acid (poly(I:C)) was well suited to generate a homogeneous cellular and humoral response against the desired epitopes. In a prophylactic setting, vaccination with the VLP displaying these epitopes resulted in total inhibition of tumor growth 1 month after vaccination. A therapeutic vaccination strategy showed a delay in grafted tumor growth or its total rejection. If the "simple" epitope display on the VLP is sufficient to prevent tumor growth, then an improved engineered platform enabling display of a large antigen is a tool to overcome the barrier of immune allele restriction, broadening the immune response, and paving the way for its potential utilization in humans as an off-the-shelf vaccine.

Adenovirus-Inspired Virus-Like-Particles Displaying Melanoma Tumor Antigen Specifically Target Human DC Subsets and Trigger Antigen-Specific Immune Responses

Virus-like particles constitute versatile vectors that can be used as vaccine platforms in many fields from infectiology and more recently to oncology. We previously designed non-infectious adenovirus-inspired 60-mer dodecahedric virus-like particles named ADDomers displaying on their surface either a short epitope or a large tumor/viral antigen. In this work, we explored for the first time the immunogenicity of ADDomers exhibiting melanoma-derived tumor antigen/epitope and their impact on the features of human dendritic cell (DC) subsets. We first demonstrated that ADDomers displaying tumor epitope/antigen elicit a strong immune-stimulating potential of human DC subsets (cDC2s, cDC1s, pDCs), which were able to internalize and cross-present tumor antigen, and subsequently cross-prime antigen-specific T-cell responses. To further limit off-target effects and enhance DC targeting, we engineered specific motifs to de-target epithelial cells and improve DCs’ addressing. The improved engineered platform making it possible to display large antigen represents a tool to overcome the barrier of immune allele restriction, broadening the immune response, and paving the way to its potential utilization in humans as an off-the-shelf vaccine.

The Effect of a Dodecahedron-Shaped Structure on the Properties of an Enzyme

In this research, the influence of a dodecahedron-shaped structure on the adsorption behavior of a horseradish peroxidase (HRP) enzyme glycoprotein onto mica substrates was studied. In the experiments, samples of an aqueous HRP solution were incubated at various distances (0.03 m, 2 m, 5 m, and control at 20 m) from the dodecahedron surface. After the incubation, the direct adsorption of HRP onto mica substrates immersed in the solutions was performed, and the mica-adsorbed HRP particles were visualized via atomic force microscopy (AFM). The effect of the increased HRP aggregation was only observed after the incubation of the enzyme solution at the 2 m distance from the dodecahedron. In addition, with respect to the control sample, spectrophotometric measurements revealed no change in the HRP enzymatic activity after the incubation at any of the distances studied. The results reported herein can be of use in the modeling of the possible influences of various spatial structures on biological objects in the development of biosensors and other electronic equipment.

Adenovirus Fibers as Ultra-Stable Vehicles for Intracellular Nanoparticle and Protein Delivery

Protein-based carriers are promising vehicles for the intracellular delivery of therapeutics. In this study, we designed and studied adenovirus protein fiber constructs with potential applications as carriers for the delivery of protein and nanoparticle cargoes. We used as a basic structural framework the fibrous shaft segment of the adenovirus fiber protein comprising of residues 61–392, connected to the fibritin foldon trimerization motif at the C-terminal end. A fourteen-amino-acid biotinylation sequence was inserted immediately after the N-terminal, His-tagged end of the construct in order to enable the attachment of a biotin moiety in vivo. We report herein that this His-tag biotinylated construct folds into thermally and protease-stable fibrous nanorods that can be internalized into cells and are not cytotoxic. Moreover, they can bind to proteins and nanoparticles through the biotin–streptavidin interaction and mediate their delivery to cells. We demonstrate that streptavidin-conjugated gold nanoparticles can be transported into NIH3T3 fibroblast and HeLa cancer cell lines. Furthermore, two streptavidin-conjugated model proteins, alkaline phosphatase and horseradish peroxidase can be delivered into the cell cytoplasm in their enzymatically active form. This work is aimed at establishing the proof-of-principle for the rational engineering of diverse functionalities onto the initial protein structural framework and the use of adenovirus fiber-based proteins as nanorods for the delivery of nanoparticles and model proteins. These constructs could constitute a stepping stone for the development of multifunctional and modular fibrous nanorod platforms that can be tailored to applications at the sequence level.

Elicitation of potent SARS-CoV-2 neutralizing antibody responses through immunization with a versatile adenovirus-inspired multimerization platform

Virus-like particles (VLPs) are highly suited platforms for protein-based vaccines. In the present work, we adapted a previously designed non-infectious adenovirus-inspired 60-mer dodecahedric VLP (ADDomer) to display a multimeric array of large antigens through a SpyTag/SpyCatcher system. To validate the platform as a potential COVID-19 vaccine approach, we decorated the newly designed VLP with the glycosylated receptor binding domain (RBD) of SARS-CoV-2. Cryoelectron microscopy structure revealed that up to 60 copies of this antigenic domain could be bound on a single ADDomer particle, with the symmetrical arrangements of a dodecahedron. Mouse immunization with the RBD decorated VLPs already showed a significant specific humoral response following prime vaccination, greatly reinforced by a single boost. Neutralization assays with SARS-CoV-2 spike pseudo-typed virus demonstrated the elicitation of strong neutralization titers, superior to those of COVID-19 convalescent patients. Notably, the presence of pre-existing immunity against the adenoviral-derived particles did not hamper the immune response against the antigen displayed on its surface. This plug and play vaccine platform represents a promising new highly versatile tool to combat emergent pathogens.

Characterization of Co-infection With Fowl Adenovirus Serotype 4 and 8a

Fowl adenoviruses (FAdVs), which are distributed worldwide, have caused considerable economic losses to poultry farms. Co-infection with FAdVs and other avian pathogens has been reported previously. However, the pathogenicity of different serotypes of FAdVs causing co-infection remains unclear. Herein, strain HN from FAdV species C serotype 4 (FAdV-4) and strain AH720 from species E serotype 8a (FAdV-8a) were used to assess the pathogenicity of their co-infection in specific-pathogen-free (SPF) chickens. Compared with chickens infected with FAdV-4 alone, those co-infected with FAdV-4 and FAdV-8a showed similar clinical symptoms, mortality rates and degree of tissue lesions, and notably decreased viral loads of HN. Conversely, the viral loads of AH720 increased markedly in the co-infection group compared with that in chickens infected with AH720 strain alone. Increased viral loads of AH720 in the liver were suspected to contribute to the pathogenicity of chickens co-infected with the HN and AH720 strains. This was further investigated by histopathology and terminal deoxynucleotidyl transferase dUTP nick-end labeling (TUNEL) staining analyses. Collectively, these data indicated that co-infection with FAdV-4 and FAdV-8a suppresses the replication and proliferation of FAdV-4 but enhances the replication and proliferation of FAdV-8a in chicken liver. This study will provide valuable information for the further investigation of the interactions between FAdV-4 and FAdV-8a during co-infection.

Adenovirus Structure: What Is New?

Adenoviruses are large (~950 Å) and complex non-enveloped, dsDNA icosahedral viruses. They have a pseudo-T = 25 triangulation number with at least 12 different proteins composing the virion. These include the major and minor capsid proteins, core proteins, maturation protease, terminal protein, and packaging machinery. Although adenoviruses have been studied for more than 60 years, deciphering their architecture has presented a challenge for structural biology techniques. An outstanding event was the first near-atomic resolution structure of human adenovirus type 5 (HAdV-C5), solved by cryo-electron microscopy (cryo-EM) in 2010. Discovery of new adenovirus types, together with methodological advances in structural biology techniques, in particular cryo-EM, has lately produced a considerable amount of new, high-resolution data on the organization of adenoviruses belonging to different species. In spite of these advances, the organization of the non-icosahedral core is still a great unknown. Nevertheless, alternative techniques such as atomic force microscopy (AFM) are providing interesting glimpses on the role of the core proteins in genome condensation and virion stability. Here we summarize the current knowledge on adenovirus structure, with an emphasis on high-resolution structures obtained since 2010.

Experimental co-infection of variant infectious bursal disease virus and fowl adenovirus serotype 4 increases mortality and reduces immune response in chickens

Infectious bursal disease virus (IBDV) and fowl adenovirus serotype 4 (FAdV-4) cause infectious bursal disease (IBD) and hydropericardium-hepatitis syndrome, respectively. Recently, studies have reported co-infections of poultry with IBDV and FAdV-4, which is an important problem in the poultry industry. Here, the variant IBDV strain ZD-2018-1 and FAdV-4 isolate HB1501 were used to assess the pathogenicity of co-infection in 1-day-old specific pathogen-free (SPF) chickens. Compared with chickens infected with only FAdV-4, those coinfected with IBDV and FAdV-4 showed enhanced clinical symptoms, higher mortality, more severe tissue lesions, and higher biochemical index levels. Furthermore, the expression of interleukin (IL)-6, IL-1β, and interferon-γ mRNAs in the IBDV-FAdV-4 coinfected chickens was delayed, and the antibody response levels were significantly lower in those birds compared with the FAdV-4-infected chickens. These results indicate that co-infection with variant IBDV ZD-2018-1 and FAdV-4 HB1501 could significantly promote the pathogenicity of FAdV-4 and reduce the immune response in chickens. This study provides the foundation for further investigation of the interaction mechanism in IBDV and FAdV-4 co-infection.