Epitope-targeting platform for broadly protective influenza vaccines

ΔA146Ply-HA stem protein immunization protects mice against influenza A virus infection and co-infection with Streptococcus pneumoniae

Influenza virus (IV) is a common pathogen affecting the upper respiratory tract, that causes various diseases. Secondary bacterial pneumonia is a common complication and a major cause of death in influenza patients. Streptococcus pneumoniae (S. pneumoniae) is the predominant co-infected bacteria in the pandemic, which colonizes healthy people but can cause diseases in immunocompromised individuals. Vaccination is a crucial strategy for avoiding infection, however, no universal influenza vaccine (UIV) that is resistant to multiple influenza viruses is available. Despite its limited immunogenicity, the hemagglutinin (HA) stem is a candidate peptide for UIV. ΔA146Ply (pneumolysin with a single deletion of A146) not only retains the Toll-like receptor 4 agonist effect but also is a potential vaccine adjuvant and a candidate protein for the S. pneumoniae vaccine. We constructed the fusion protein ΔA146Ply-HA stem and studied its immunoprotective effect in mice infection models. The results showed that intramuscular immunization of ΔA146Ply-HA stem without adjuvant could induce specific antibodies against HA stem and specific CD4+ T and CD8+ T cellular immunity in BALB/c and C57BL/6 mice, which could improve the survival rate of mice infected with IAV and co-infected with S. pneumoniae, but the protective effect on BALB/c mice was better than that on C57BL/6 mice. ΔA146Ply-HA stem serum antibody could protect BALB/c and C57BL/6 mice from IAV, and recognized HA polypeptides of H3N2, H5N1, H7N9, and H9N2 viruses. Moreover, ΔA146Ply-HA stem intramuscular immunization had a high safety profile with no obvious toxic side effects. The results indicated that coupling ΔA146Ply with influenza protein as a vaccine was a safe and effective strategy against the IV and secondary S. pneumoniae infection.

Self-assembled multiepitope nanovaccine based on NoV P particles induces effective and lasting protection against H3N2 influenza virus

Current seasonal influenza vaccines confer only limited coverage of virus strains due to the frequent genetic and antigenic variability of influenza virus (IV). Epitope vaccines that accurately target conserved domains provide a promising approach to increase the breadth of protection; however, poor immunogenicity greatly hinders their application. The protruding (P) domain of the norovirus (NoV), which can self-assemble into a 24-mer particle called the NoV P particle, offers an ideal antigen presentation platform. In this study, a multiepitope nanovaccine displaying influenza epitopes (HMN-PP) was constructed based on the NoV P particle nanoplatform. Large amounts of HMN-PP were easily expressed in Escherichia coli in soluble form. Animal experiments showed that the adjuvanted HMN-PP nanovaccine induced epitope-specific antibodies and haemagglutinin (HA)-specific neutralizing antibodies, and the antibodies could persist for at least three months after the last immunization. Furthermore, HMN-PP induced matrix protein 2 extracellular domain (M2e)-specific antibody-dependent cell-mediated cytotoxicity, CD4+ and CD8+ T-cell responses, and a nucleoprotein (NP)-specific cytotoxic T lymphocyte (CTL) response. These results indicated that the combination of a multiepitope vaccine and self-assembled NoV P particles may be an ideal and effective vaccine strategy for highly variable viruses such as IV and SARS-CoV-2.

Electronic Supplementary Material

Supplementary material is available in the online version of this article at 10.1007/s12274-023-5395-6.

Anti-neuraminidase and anti-hemagglutinin immune serum can confer inter-lineage cross protection against recent influenza B

Influenza B viruses (IBV) are responsible for a considerable part of the burden caused by influenza virus infections. Since their emergence in the 1980s, the Yamagata and Victoria antigenic lineages of influenza B circulate in alternate patterns across the globe. Furthermore, their evolutionary divergence and the appearance of new IBV subclades complicates the prediction of future influenza vaccines compositions. It has been proposed that the addition of the neuraminidase (NA) antigen could potentially induce a broader protection and compensate for hemagglutinin (HA) mismatches in the current vaccines. Here we show that anti-NA and -HA sera against both Victoria and Yamagata lineages have limited inter-lineage cross-reactivity. When transferred to mice prior to infection with a panel of IBVs, anti-NA sera were as potent as anti-HA sera in conferring protection against homologous challenge and, in some cases, conferred superior protection against challenge with heterologous IBV strains.

Broadly Protective Neuraminidase-Based Influenza Vaccines and Monoclonal Antibodies: Target Epitopes and Mechanisms of Action

Neuraminidase (NA) is an important surface protein on influenza virions, playing an essential role in the viral life cycle and being a key target of the immune system. Despite the importance of NA-based immunity, current vaccines are focused on the hemagglutinin (HA) protein as the target for protective antibodies, and the amount of NA is not standardized in virion-based vaccines. Antibodies targeting NA are predominantly protective, reducing infection severity and viral shedding. Recently, NA-specific monoclonal antibodies have been characterized, and their target epitopes have been identified. This review summarizes the characteristics of NA, NA-specific antibodies, the mechanism of NA inhibition, and the recent efforts towards developing NA-based and NA-incorporating influenza vaccines.

Layered protein nanoparticles containing influenza B HA stalk induced sustained cross-protection against viruses spanning both viral lineages

The influenza epidemics pose a significant threat to public health. Of them, type B influenza coincided with several severe flu outbreaks. The efficacy of the current seasonal flu vaccine is limited due to the antigenicity changes of circulating strains. In this study, we generated structure-stabilized HA stalk antigens from influenza B and fabricated double-layered protein nanoparticles as universal influenza B vaccine candidates. In vitro studies found that the resulting protein nanoparticles were effectively taken up to activate dendritic cells. Nanoparticle immunization induced broadly reactive immune responses conferring robust and sustained cross-immune protection against influenza B virus strains of both lineages. The results reveal the potential of layered protein nanoparticles incorporated with structure-stabilized constant antigens as a universal influenza vaccine with improved immune protective potency and breadth.

Cross-Protection Induced by Virus-like Particles Derived from the Influenza B Virus

The mismatch between the circulating influenza B virus (IBV) and the vaccine strain contributes to the rapid emergence of IBV infection cases throughout the globe, which necessitates the development of effective vaccines conferring broad protection. Here, we generated influenza B virus-like particle (VLP) vaccines expressing hemagglutinin, neuraminidase, or both antigens derived from the influenza B virus (B/Washington/02/2019 (B/Victoria lineage)-like virus, B/Phuket/3073/2013 (B/Yamagata lineage)-like virus. We found that irrespective of the derived antigen lineage, immunizing mice with the IBV VLPs significantly reduced lung viral loads, minimized bodyweight loss, and ensured 100% survival upon Victoria lineage virus B/Colorado/06/2017 challenge infection. These results were closely correlated with the vaccine-induced antibody responses and HI titer in sera, IgG, IgA antibody responses, CD4+ and CD8+ T cell responses, germinal center B cell responses, and inflammatory cytokine responses in the lungs. We conclude that hemagglutinin, neuraminidase, or both antigen-expressing VLPs derived from these influenza B viruses that were circulating during the 2020/21 season provide cross-protections against mismatched Victoria lineage virus (B/Colorado/06/2017) challenge infections.

Influenza Neuraminidase Characteristics and Potential as a Vaccine Target

Neuraminidase of influenza A and B viruses plays a critical role in the virus life cycle and is an important target of the host immune system. Here, we highlight the current understanding of influenza neuraminidase structure, function, antigenicity, immunogenicity, and immune protective potential. Neuraminidase inhibiting antibodies have been recognized as correlates of protection against disease caused by natural or experimental influenza A virus infection in humans. In the past years, we have witnessed an increasing interest in the use of influenza neuraminidase to improve the protective potential of currently used influenza vaccines. A number of well-characterized influenza neuraminidase-specific monoclonal antibodies have been described recently, most of which can protect in experimental challenge models by inhibiting the neuraminidase activity or by Fc receptor-dependent mechanisms. The relative instability of the neuraminidase poses a challenge for protein-based antigen design. We critically review the different solutions that have been proposed to solve this problem, ranging from the inclusion of stabilizing heterologous tetramerizing zippers to the introduction of inter-protomer stabilizing mutations. Computationally engineered neuraminidase antigens have been generated that offer broad, within subtype protection in animal challenge models. We also provide an overview of modern vaccine technology platforms that are compatible with the induction of robust neuraminidase-specific immune responses. In the near future, we will likely see the implementation of influenza vaccines that confront the influenza virus with a double punch: targeting both the hemagglutinin and the neuraminidase.