Flu Universal Vaccines: New Tricks on an Old Virus

Impact of glycosylation on viral vaccines

Glycosylation is the most prominent modification important for vaccines and its specific pattern depends on several factors that need to be considered when developing a new biopharmaceutical. Tailor-made glycosylation can be exploited to develop more effective and safer vaccines; for this reason, a deep understanding of both glycoengineering strategies and glycans structures and functions is required. In this review we discuss the recent advances concerning glycoprotein expression systems and the explanation of glycans immunomodulation mechanisms. Furthermore, we highlight how glycans tune the immunological properties among different vaccines platforms (whole virus, recombinant protein, nucleic acid), also comparing commercially available formulations and describing the state-of-the-art analytical technologies for glycosylation analysis. The whole review stresses the aspect of glycoprotein glycans as a potential tool to overcome nowadays medical needs in vaccine field.

Protection against the H1N1 influenza virus using self-assembled nanoparticles formed by lumazine synthase and bearing the M2e peptide

There is an urgent need for influenza vaccines that offer broad cross-protection. The highly conserved ectodomain of the influenza matrix protein 2 (M2e) is a promising candidate; however, its low immunogenicity can be addressed. In this study, we developed influenza vaccines using the Lumazine synthase (LS) platform. The primary objective of this study was to determine the protective potential of M2e proteins expressed on Lumazine synthase (LS) nanoparticles. M2e-LS proteins, produced through the E. coli system, spontaneously assemble into nanoparticles. The study investigated the efficacy of the M2e-LS nanoparticle vaccine in mice. Mice immunized with M2e-LS nanoparticles exhibited significantly higher levels of intracellular cytokines than those receiving soluble M2e proteins. The M2e-LS protein exhibited robust immunogenicity and provided 100% protection against cross-clade influenza.

Influenza Virus-Derived CD8 T Cell Epitopes: Implications for the Development of Universal Influenza Vaccines

The influenza virus poses a global health burden. Currently, an annual vaccine is used to reduce influenza virus-associated morbidity and mortality. Most influenza vaccines have been developed to elicit neutralizing Abs against influenza virus. These Abs primarily target immunodominant epitopes derived from hemagglutinin (HA) or neuraminidase (NA) of the influenza virus incorporated in vaccines. However, HA and NA are highly variable proteins that are prone to antigenic changes, which can reduce vaccine efficacy. Therefore, it is essential to develop universal vaccines that target immunodominant epitopes derived from conserved regions of the influenza virus, enabling cross-protection among different virus variants. The internal proteins of the influenza virus serve as ideal targets for universal vaccines. These internal proteins are presented by MHC class I molecules on Ag-presenting cells, such as dendritic cells, and recognized by CD8 T cells, which elicit CD8 T cell responses, reducing the likelihood of disease and influenza viral spread by inducing virus-infected cell apoptosis. In this review, we highlight the importance of CD8 T cell-mediated immunity against influenza viruses and that of viral epitopes for developing CD8 T cell-based influenza vaccines.

Mosaic quadrivalent influenza vaccine single nanoparticle characterization

Recent work by our laboratory and others indicates that co-display of multiple antigens on protein-based nanoparticles may be key to induce cross-reactive antibodies that provide broad protection against disease. To reach the ultimate goal of a universal vaccine for seasonal influenza, a mosaic influenza nanoparticle vaccine (FluMos-v1) was developed for clinical trial (NCT04896086). FluMos-v1 is unique in that it is designed to co-display four recently circulating haemagglutinin (HA) strains; however, current vaccine analysis techniques are limited to nanoparticle population analysis, thus, are unable to determine the valency of an individual nanoparticle. For the first time, we demonstrate by total internal reflection fluorescence microscopy and supportive physical-chemical methods that the co-display of four antigens is indeed achieved in single nanoparticles. Additionally, we have determined percentages of multivalent (mosaic) nanoparticles with four, three, or two HA proteins. The integrated imaging and physicochemical methods we have developed for single nanoparticle multivalency will serve to further understand immunogenicity data from our current FluMos-v1 clinical trial.

Single-Component Multilayered Self-Assembling Protein Nanoparticles Displaying Extracellular Domains of Matrix Protein 2 as a Pan-influenza A Vaccine

The development of a cross-protective pan-influenza A vaccine remains a significant challenge. In this study, we designed and evaluated single-component self-assembling protein nanoparticles (SApNPs) presenting the conserved extracellular domain of matrix protein 2 (M2e) as vaccine candidates against influenza A viruses. The SApNP-based vaccine strategy was first validated for human M2e (hM2e) and then applied to tandem repeats of M2e from human, avian, and swine hosts (M2ex3). Vaccination with M2ex3 displayed on SApNPs demonstrated higher survival rates and less weight loss compared to the soluble M2ex3 antigen against the lethal challenges of H1N1 and H3N2 in mice. M2ex3 I3-01v9a SApNPs formulated with a squalene-based adjuvant were retained in the lymph node follicles over 8 weeks and induced long-lived germinal center reactions. Notably, a single low dose of M2ex3 I3-01v9a SApNP formulated with a potent adjuvant, either a Toll-like receptor 9 (TLR9) agonist or a stimulator of interferon genes (STING) agonist, conferred 90% protection against a lethal H1N1 challenge in mice. With the ability to induce robust and durable M2e-specific functional antibody and T cell responses, the M2ex3-presenting I3-01v9a SApNP provides a promising pan-influenza A vaccine candidate.

Influenza virus cell entry and targeted antiviral development

Influenza virus infection is currently one of the most prevalent and transmissible diseases in the world causing local outbreaks every year. It has the potential to cause devastating global pandemics as well. The development of anti-influenza drugs possessing novel mechanisms of action is urgently needed to control the spread of influenza infections; thus, drugs that inhibit influenza virus entry into target cells are emerging as a hot research topic. In addition to discussing the biological significance of hemagglutinin in viral replication, this article provides recent updates on the natural products, small molecules, proteins, peptides, and neutralizing antibody-like proteins that have anti-influenza potency.

Optimization and applications of an in vivo bioluminescence imaging model of influenza A virus infections

•The in vivo BLI model of IAV infections can simplify the determination of viral load in living animals. •The in vivo BLI model of IAV infections allow longitudinal measurements of virus infection/spread in living animals. •The in vivo BLI model of IAV infections improved the throughput of animal models. •The advanced BLI models can facilitate studies in both basic and applied virology.

Differential recognition of influenza A virus H1N1 neuraminidase by DNA vaccine-induced antibodies in pigs and ferrets

Neuraminidase (NA) accounts for approximately 10-20% of the total glycoproteins on the surface of influenza viruses. It cleaves sialic acids on glycoproteins, which facilitates virus entry into the airways by cleaving heavily glycosylated mucins in mucus and the release of progeny virus from the surface of infected cells. These functions make NA an attractive vaccine target. To inform rational vaccine design, we define the functionality of influenza DNA vaccine-induced NA-specific antibodies relative to antigenic sites in pigs and ferrets challenged with a vaccine-homologous A/California/7/2009(H1N1)pdm09 strain. Sera collected pre-vaccination, post-vaccination and post-challenge were analyzed for antibody-mediated inhibition of NA activity using a recombinant H7N1_CA09 virus. Antigenic sites were further identified with linear and conformational peptide microarrays spanning the full NA of A/California/04/2009(H1N1)pdm09. Vaccine-induced NA-specific antibodies inhibited the enzymatic function of NA in both animal models. The antibodies target critical sites of NA such as the enzymatic site, second sialic binding site and framework residues, shown here by high-resolution epitope mapping. New possible antigenic sites were identified that potentially block the catalytic activity of NA, including an epitope recognized solely in pigs and ferrets with neuraminidase inhibition, which could be a key antigenic site affecting NA function. These findings show that our influenza DNA vaccine candidate induces NA-specific antibodies that target known critical sites, and new potential antigenic sites of NA, inhibiting the catalytic activity of NA.

Revisiting influenza A virus life cycle from a perspective of genome balance

Influenza A virus (IAV) genome comprises eight negative-sense RNA segments, of which the replication is well orchestrated and the delicate balance of multiple segments are dynamically regulated throughout IAV life cycle. However, previous studies seldom discuss these balances except for functional hemagglutinin-neuraminidase balance that is pivotal for both virus entry and release. Therefore, we attempt to revisit IAV life cycle by highlighting the critical role of "genome balance". Moreover, we raise a "balance regression" model of IAV evolution that the virus evolves to rebalance its genome after reassortment or interspecies transmission, and direct a "balance compensation" strategy to rectify the "genome imbalance" as a result of artificial modifications during creation of recombinant IAVs. This review not only improves our understanding of IAV life cycle, but also facilitates both basic and applied research of IAV in future.

Improving cross-protection against influenza virus in mice using a nanoparticle vaccine of mini-HA

This study aimed to investigate the protective effect of mini-hemagglutinin (mini-HA) proteins expressed on lumazine synthase (LS) nanoparticles against influenza. Soluble mini-HA proteins were assembled with LS proteins via SpyTag/SpyCatcher in vitro. The size of mini-HA-LS nanoparticles was characterized by transmission electron microscopy (TEM) and dynamic light scattering (DLS), and the effect of mini-HA-LS nano-vaccines was explored in mice. The results indicate that the diameter of mini-HA-LS nanoparticles was approximately 60-80 nm. The nanoparticles could induce stronger humoral and cellular immune responses and produce cross-clade protection against influenza in mice.

SARS-CoV-2 cell entry and targeted antiviral development

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is the causative agent of the pandemic coronavirus disease 2019 (COVID-19), which threatens human health and public safety. In the urgent campaign to develop anti-SARS-CoV-2 therapies, the initial entry step is one of the most appealing targets. In this review, we summarize the current understanding of SARS-CoV-2 cell entry, and the development of targeted antiviral strategies. Moreover, we speculate upon future directions toward next-generation of SARS-CoV-2 entry inhibitors during the upcoming post-pandemic era.

Protective Efficacy of Recombinant Influenza Hemagglutinin Ectodomain Fusions

In current seasonal influenza vaccines, neutralizing antibody titers directed against the hemagglutinin surface protein are the primary correlate of protection. These vaccines are, therefore, quantitated in terms of their hemagglutinin content. Adding other influenza surface proteins, such as neuraminidase and M2e, to current quadrivalent influenza vaccines would likely enhance vaccine efficacy. However, this would come with increased manufacturing complexity and cost. To address this issue, as a proof of principle, we have designed genetic fusions of hemagglutinin ectodomains from H3 and H1 influenza A subtypes. These recombinant H1-H3 hemagglutinin ectodomain fusions could be transiently expressed at high yield in mammalian cell culture using Expi293F suspension cells. Fusions were trimeric, and as stable in solution as their individual trimeric counterparts. Furthermore, the H1-H3 fusion constructs were antigenically intact based on their reactivity with a set of conformation-specific monoclonal antibodies. H1-H3 hemagglutinin ectodomain fusion immunogens, when formulated with the MF59 equivalent adjuvant squalene-in-water emulsion (SWE), induced H1 and H3-specific humoral immune responses equivalent to those induced with an equimolar mixture of individually expressed H1 and H3 ectodomains. Mice immunized with these ectodomain fusions were protected against challenge with heterologous H1N1 (Bel/09) and H3N2 (X-31) mouse-adapted viruses with higher neutralizing antibody titers against the H1N1 virus. Use of such ectodomain-fused immunogens would reduce the number of components in a vaccine formulation and allow for the inclusion of other protective antigens to increase influenza vaccine efficacy.

Small Molecule Inhibitors of Influenza Virus Entry

Hemagglutinin (HA) plays a critical role during influenza virus receptor binding and subsequent membrane fusion process, thus HA has become a promising drug target. For the past several decades, we and other researchers have discovered a series of HA inhibitors mainly targeting its fusion machinery. In this review, we summarize the advances in HA-targeted development of small molecule inhibitors. Moreover, we discuss the structural basis and mode of action of these inhibitors, and speculate upon future directions toward more potent inhibitors of membrane fusion and potential anti-influenza drugs.

Construction and Immunogenicity of Modified mRNA-Vaccine Variants Encoding Influenza Virus Antigens

Nucleic acid-based influenza vaccines are a promising platform that have recently and rapidly developed. We previously demonstrated the immunogenicity of DNA vaccines encoding artificial immunogens AgH1, AgH3, and AgM2, which contained conserved fragments of the hemagglutinin stem of two subtypes of influenza A-H1N1 and H3N2-and conserved protein M2. Thus, the aim of this study was to design and characterize modified mRNA obtained using the above plasmid DNA vaccines as a template. To select the most promising protocol for creating highly immunogenic mRNA vaccines, we performed a comparative analysis of mRNA modifications aimed at increasing its translational activity and decreasing toxicity. We used mRNA encoding a green fluorescent protein (GFP) as a model. Eight mRNA-GFP variants with different modifications (M0-M7) were obtained using the classic cap(1), its chemical analog ARCA (anti-reverse cap analog), pseudouridine (Ψ), N6-methyladenosine (m6A), and 5-methylcytosine (m5C) in different ratios. Modifications M2, M6, and M7, which provided the most intensive fluorescence of transfected HEK293FT cells were used for template synthesis when mRNA encoded influenza immunogens AgH1, AgH3, and AgM2. Virus specific antibodies were registered in groups of animals immunized with a mix of mRNAs encoding AgH1, AgH3, and AgM2, which contained either ARCA (with inclusions of 100% Ψ and 20% m6A (M6)) or a classic cap(1) (with 100% substitution of U with Ψ (M7)). M6 modification was the least toxic when compared with other mRNA variants. M6 and M7 RNA modifications can therefore be considered as promising protocols for designing mRNA vaccines.