Progress in Adenoviral Capsid-Display Vaccines

Modular capsid decoration boosts adenovirus vaccine-induced humoral immunity against SARS-CoV-2

Adenovirus vector vaccines have been widely and successfully deployed in response to coronavirus disease 2019 (COVID-19). However, despite inducing potent T cell immunity, improvement of vaccine-specific antibody responses upon homologous boosting is modest compared with other technologies. Here, we describe a system enabling modular decoration of adenovirus capsid surfaces with antigens and demonstrate potent induction of humoral immunity against these displayed antigens. Ligand attachment via a covalent bond was achieved using a protein superglue, DogTag/DogCatcher (similar to SpyTag/SpyCatcher), in a rapid and spontaneous reaction requiring only co-incubation of ligand and vector components. DogTag was inserted into surface-exposed loops in the adenovirus hexon protein to allow attachment of DogCatcher-fused ligands on virus particles. Efficient coverage of the capsid surface was achieved using various ligands, with vector infectivity retained in each case. Capsid decoration shielded particles from vector neutralizing antibodies. In prime-boost regimens, adenovirus vectors decorated with the receptor-binding domain of severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) spike induced >10-fold higher SARS-CoV-2 neutralization titers compared with an undecorated vector encoding spike. Importantly, decorated vectors achieved equivalent or superior T cell immunogenicity against encoded antigens compared with undecorated vectors. We propose capsid decoration using protein superglues as a novel strategy to improve efficacy and boostability of adenovirus-based vaccines and therapeutics.

Hexon modification of human adenovirus type 5 vectors enables efficient transduction of human multipotent mesenchymal stromal cells

In adenovirus type 5 (HAdV-5)-derived viral vectors, the fiber protein has been the preferred locale for modifications to alter the natural viral tropism. Hexon, the most abundant capsid protein, has rarely been used for retargeting purposes, likely because the insertion of larger targeting peptides into Hexon often interferes with the assembly of the viral capsid. We previously observed that positively charged molecules enhance the transduction of human multipotent mesenchymal stromal cells (hMSCs)—a cell type of significant interest for clinical development but inefficiently transduced by unmodified HAdV-5-based vectors. As efficient HAdV-5-mediated gene transfer would greatly increase the therapeutic potential of hMSCs, we tested the hypothesis that introducing positively charged amino acids into Hexon might enhance the transduction of hMSCs, enabling efficient expression of selected transgenes. From the constructs that could be rescued as functional virions, one (HAdV-5-HexPos3) showed striking transduction of hMSCs with up to 500-fold increased efficiency. Evaluation of the underlying mechanism identified heparan sulfate proteoglycans (HSPGs) to be essential for virus uptake by the cells. The ease and efficiency of transduction of hMSCs with this vector will facilitate the development of genetically modified hMSCs as therapeutic vehicles in different disciplines, including oncology or regenerative medicine.

Adenovirus-based vaccines - a platform for pandemic preparedness against emerging viral pathogens

Zoonotic viruses continually pose a pandemic threat. Infection of humans with viruses for which we typically have little or no prior immunity can result in epidemics with high morbidity and mortality. These epidemics can have public health and economic impact and can exacerbate civil unrest or political instability. Changes in human behavior in the past few decades—increased global travel, farming intensification, the exotic animal trade, and the impact of global warming on animal migratory patterns, habitats, and ecosystems—contribute to the increased frequency of cross-species transmission events. Investing in the pre-clinical advancement of vaccine candidates against diverse emerging viral threats is crucial for pandemic preparedness. Replication-defective adenoviral (Ad) vectors have demonstrated their utility as an outbreak-responsive vaccine platform during the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) pandemic. Ad vectors are easy to engineer; are amenable to rapid, inexpensive manufacturing; are relatively safe and immunogenic in humans; and, importantly, do not require specialized cold-chain storage, making them an ideal platform for equitable global distribution or stockpiling. In this review, we discuss the progress in applying Ad-based vaccines against emerging viruses and summarize their global safety profile, as reflected by their widespread geographic use during the SARS-CoV-2 pandemic.

Chemically induced protein cage assembly with programmable opening and cargo release

Engineered protein cages are promising tools that can be customized for applications in medicine and nanotechnology. A major challenge is developing a straightforward strategy for endowing cages with bespoke, inducible disassembly. Such cages would allow release of encapsulated cargoes at desired timing and location. Here, we achieve such programmable disassembly using protein cages, in which the subunits are held together by different molecular cross-linkers. This modular system enables cage disassembly to be controlled in a condition-dependent manner. Structural details of the resulting cages were determined using cryo–electron microscopy, which allowed observation of bridging cross-linkers at intended positions. Triggered disassembly was demonstrated by high-speed atomic force microscopy and subsequent cargo release using an encapsulated Förster resonance energy transfer pair whose signal depends on the quaternary structure of the cage.

Understanding Post Entry Sorting of Adenovirus Capsids; A Chance to Change Vaccine Vector Properties

Adenovirus vector-based genetic vaccines have emerged as a powerful strategy against the SARS-CoV-2 health crisis. This success is not unexpected because adenoviruses combine many desirable features of a genetic vaccine. They are highly immunogenic and have a low and well characterized pathogenic profile paired with technological approachability. Ongoing efforts to improve adenovirus-vaccine vectors include the use of rare serotypes and non-human adenoviruses. In this review, we focus on the viral capsid and how the choice of genotypes influences the uptake and subsequent subcellular sorting. We describe how understanding capsid properties, such as stability during the entry process, can change the fate of the entering particles and how this translates into differences in immunity outcomes. We discuss in detail how mutating the membrane lytic capsid protein VI affects species C viruses' post-entry sorting and briefly discuss if such approaches could have a wider implication in vaccine and/or vector development.

Codon Usage and Adenovirus Fitness: Implications for Vaccine Development

Vaccination is the most effective method to date to prevent viral diseases. It intends to mimic a naturally occurring infection while avoiding the disease, exposing our bodies to viral antigens to trigger an immune response that will protect us from future infections. Among different strategies for vaccine development, recombinant vaccines are one of the most efficient ones. Recombinant vaccines use safe viral vectors as vehicles and incorporate a transgenic antigen of the pathogen against which we intend to generate an immune response. These vaccines can be based on replication-deficient viruses or replication-competent viruses. While the most effective strategy involves replication-competent viruses, they must be attenuated to prevent any health hazard while guaranteeing a strong humoral and cellular immune response. Several attenuation strategies for adenoviral-based vaccine development have been contemplated over time. In this paper, we will review them and discuss novel approaches based on the principle that protein synthesis from individual genes can be modulated by codon usage bias manipulation. We will summarize vaccine approaches that consider recoding of viral proteins to produce adenoviral attenuation and recoding of the transgene antigens for both viral attenuation and efficient viral epitope expression.

Structural Organization and Protein-Protein Interactions in Human Adenovirus Capsid

Human adenoviruses (HAdVs) are large (150 MDa), complex, nonenveloped dsDNA viruses that cause self-limiting respiratory, ocular and enteric infections. They are significant health hazard in young, elderly and immuno-compromised populations. Moreover, various adenoviruses (AdVs) of mammalian origin are being used as vectors in gene, vaccine and cancer therapies. Multiple copies of at least 13 different proteins, all in all ~2800 protein molecules, come together to form an adenovirus virion packaging the ~36 Kbp geome. The details of structural organization of the adenovirus capsid and underlying network of protein-protein interactions provide clues into designing the modified and novel adenovirus vectors with desired functionalities and/or targeting specificities. The advancements in 3D structure determination by cryo-electron microscopy (cryo-EM) in the past decade have enabled unveiling of the complex organization of adenovirus architecture at near atomic resolution. Specifically, these studies revealed the structures and the network of interactions involving cement/minor proteins in stabilizing the AdV icosahedral architecture, which appear to be mostly conserved among human adenoviruses. In this chapter, we describe the current state of knowledge on the structure and organization of human adenoviruses.

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

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

Fusion of Large Polypeptides to Human Adenovirus Type 5 Capsid Protein IX Can Compromise Virion Stability and DNA Packaging Capacity

The human adenovirus (HAdV) protein IX (pIX) is a minor component of the capsid that acts in part to stabilize the hexon-hexon interactions within the mature capsid. Virions lacking pIX have a reduced DNA packaging capacity and exhibit thermal instability. More recently, pIX has been developed as a platform for presentation of large polypeptides, such as fluorescent proteins or large targeting ligands, on the viral capsid. It is not known whether such modifications affect the natural ability of pIX to stabilize the HAdV virion. In this study, we show that addition of large polypeptides to pIX does not alter the natural stability of virions containing sub-wild-type-sized genomes. However, similar virions containing wild-type-sized genomes tend to genetically rearrange, likely due to selective pressure caused by virion instability as a result of compromised pIX function.IMPORTANCE Human adenovirus capsid protein IX (pIX) is involved in stabilizing the virion but has also been developed as a platform for presentation of various polypeptides on the surface of the virion. Whether such modifications affect the ability of pIX to stabilize the virion is unknown. We show that addition of large polypeptides to pIX can reduce both the DNA packaging capacity and the heat stability of the virion, which provides important guidance for the design of pIX-modified vectors.

Therapeutic Vaccines Against Human Papilloma Viruses: Achievements and Prospects

Human papillomaviruses of high carcinogenic risk (HR HPVs) are major etiological agents of malignant diseases of the cervix, vulva, penis, anal canal, larynx, head, and neck. Prophylactic vaccination against HPV, which mainly covers girls and women under 25, does not prevent vertical and horizontal HPV transmission in infants and children and does not have a therapeutic effect. As a result, a significant proportion of the population is not protected from the HPV infection and development of HPV-associated neoplastic transformation and cancer, which indicates the need for development and introduction of therapeutic HPV vaccines. Unlike prophylactic vaccines aimed at the formation of virus-neutralizing antibodies, therapeutic vaccines elicit cellular immune response leading to the elimination of infected and malignant cells expressing viral proteins. The ideal targets for vaccine immunotherapy are highly conserved HR HPV oncoproteins E6 and E7 expressed in precancerous and tumor tissues. Here, we describe expression of these proteins during different stages of HPV infection, their antigenic and immunogenic properties, and T-cell epitopes, the response to which correlates with natural regression of HPV-induced neoplastic changes. The review describes patterns of E6 and E7 oncoproteins presentation to the immune system as components of candidate vaccines along with the results of the most promising preclinical trials and animal models used in these trials. Special attention is paid to vaccine candidates which have shown efficacy in clinical trials in patients with HPV-associated neoplastic changes.

Site-directed modification of adenoviral vector with combined DNA assembly and restriction-ligation cloning

Commonly used and well accepted approaches are lacking for site-directed modification of adenoviral vectors. Here, we attempt to introduce an easy-to-implement strategy for such purpose with an example of establishing a replication competent adenoviral vector system from pKAd5 plasmid, an infectious clone of human adenovirus 5 (HAdV-5). PCR products of GFP expression cassette and plasmid backbone were fused with the EcoRI/NdeI-digested fragment of pKAd5 to generate a modified intermediate plasmid pMDXE3GA by DNA assembly. NdeI-digested fragment of pMDXE3GA was brought back to pKAd5 to form the adenoviral plasmid pKAd5XE3GA by restriction-ligation cloning. Recombinant adenovirus HAdV5-XE3GA was rescued, amplified and purified. The expression of GFP and the propagation of virus in adherent HEp-2 and suspension K562 cells were investigated. Expression of target gene was significantly enhanced in both cell lines infected with HAdV5-XE3GA due to virus replication. However, propagation of virus could not sustain in culture of K562 cells. Shuttle plasmid pSh5RC-GFP was constructed to facilitate exchange of transgene. In summary, the strategy of combined DNA assembly and restriction-ligation cloning is functional, cost-effective and suitable for genetic modification of adenovirus.

An outbreak of epidemic keratoconjunctivitis caused by human adenovirus type 8 in primary school, southwest China

Background

Two outbreaks of epidemic keratoconjunctivitis (EKC) occurred successively with an interval of 5 days in two primary boarding schools in Weixi Lisu Autonomous County, Diqing, and Tibetan Autonomous Prefecture, Yunnan. The aims of this study were to determine the intensity and characteristics of the outbreaks, as well as the clinical manifestations in the patients, the risk factors for infection and the pathogen responsible for the two outbreaks.

Methods

An outbreak investigation was conducted in two primary schools, and a case-control study including patients from the Weixi County Ethnic Primary School was performed. Relevant specimens were collected according to the case definition, and next-generation sequencing was employed to identify the pathogen. An epidemiological investigation method was used to analyse the related epidemiological characteristics, such as risk factors. The phylogenetic tree was constructed by MEGA 7.0.

Results

A total of 331 acute conjunctivitis cases, including probable cases of EKC, were reported in the two schools, and the attack rates were 30.59% (171/559, 95%CI: 26.76–34.42) and 20.41% (160/784, 95%CI: 17.58–23.24), respectively. Cases occurred in all grades and classes in both schools, and only one staff member in each school presented illness. The epidemics lasted for 54 days and 45 days, respectively. The patients had typical manifestations of EKC, such as acute onset, follicular hyperplasia, pseudomembrane formation, preauricular lymphadenopathy, corneal involvement and blurred vision, and a relatively long disease course (average 9.40 days, longest 23 days and shortest 7 days). The risk factor for infection was close contact with a patient or personal items contaminated by a patient. The pathogen responsible for the outbreaks was HAdV-8. The virus was highly similar to the 2016 HAdV-8 strain from Tibet, China.

Conclusions

This study strongly suggests that HAdV-8 could lead to serious consequences. This is the second report of a HAdV-8-associated EKC outbreak in mainland China. Tibetan HAdV-8 might be circulating in southwest China; therefore, it is necessary to monitor the pathogens causing acute conjunctivitis in this area.

Capsid-Incorporation Strategy To Display Antigens for an Alternative Adenoviral Vector Vaccine Approach

The adenovirus (Ad) is widely used as a vaccine because of its ability to induce a cellular and humoral immune response. In addition, human clinical trials have validated the safety and efficacy of Ad as a vaccine vector. The traditional approach for employing the adenovirus as vaccine is to configure the antigen genes into the expression cassette of the Ad genome. An alternative method for inducing an immune response is the "capsid-incorporation" strategy. This strategy is based upon the incorporation of proteins or peptides into the capsid proteins. This review will focus on the established uses of this approach as well as highlighting the new developments regarding the capsid-incorporation strategy.