Interferon mediated prophylactic protection against respiratory viruses conferred by a prototype live attenuated influenza virus vaccine lacking non-structural protein 1

Mucosal Immunization with an Influenza Vector Carrying SARS-CoV-2 N Protein Protects Naïve Mice and Prevents Disease Enhancement in Seropositive Th2-Prone Mice

Background/Objectives: Intranasal vaccination enhances protection against respiratory viruses by providing stimuli to the immune system at the primary site of infection, promoting a balanced and effective response. Influenza vectors with truncated NS1 are a promising vaccine approach that ensures a pronounced local CD8+ T-cellular immune response. Here, we describe the protective and immunomodulating properties of an influenza vector FluVec-N carrying the C-terminal fragment of the SARS-CoV-2 nucleoprotein within a truncated NS1 open reading frame. Methods: We generated several FluVec-N recombinant vectors by reverse genetics and confirmed the vector's genetic stability, antigen expression in vitro, attenuation, and immunogenicity in a mouse model. We tested the protective potential of FluVec-N intranasal immunization in naïve mice and seropositive Th2-prone mice, primed with aluminium-adjuvanted inactivated SARS-CoV-2. Immune response in immunized and challenged mice was analyzed through serological methods and flow cytometry. Results: Double intranasal immunization of naïve mice with FluVec-N reduced weight loss and viral load in the lungs following infection with the SARS-CoV-2 beta variant. Mice primed with alum-adjuvanted inactivated coronavirus experienced substantial early weight loss and eosinophilia in the lungs during infection, demonstrating signs of enhanced disease. A single intranasal boost immunization with FluVec-N prevented the disease enhancement in primed mice by modulating the local immune response. Protection was associated with the formation of specific IgA and the early activation of virus-specific effector and resident CD8+ lymphocytes in mouse lungs. Conclusions: Our study supports the potential of immunization with influenza vector vaccines to prevent respiratory diseases and associated immunopathology.

Sequential immunization with chimeric hemagglutinin ΔNS1 attenuated influenza vaccines induces broad humoral and cellular immunity

Influenza viruses pose a threat to public health as evidenced by severe morbidity and mortality in humans on a yearly basis. Given the constant changes in the viral glycoproteins owing to antigenic drift, seasonal influenza vaccines need to be updated periodically and effectiveness often drops due to mismatches between vaccine and circulating strains. In addition, seasonal influenza vaccines are not protective against antigenically shifted influenza viruses with pandemic potential. Here, we have developed a highly immunogenic vaccination regimen based on live-attenuated influenza vaccines (LAIVs) comprised of an attenuated virus backbone lacking non-structural protein 1 (ΔNS1), the primary host interferon antagonist of influenza viruses, with chimeric hemagglutinins (cHA) composed of exotic avian head domains with a highly conserved stalk domain, to redirect the humoral response towards the HA stalk. In this study, we showed that cHA-LAIV vaccines induce robust serum and mucosal responses against group 1 stalk and confer antibody-dependent cell cytotoxicity activity. Mice that intranasally received cH8/1-ΔNS1 followed by a cH11/1-ΔNS1 heterologous booster had robust humoral responses for influenza A virus group 1 HAs and were protected from seasonal H1N1 influenza virus and heterologous highly pathogenic avian H5N1 lethal challenges. When compared with mice immunized with the standard of care or cold-adapted cHA-LAIV, cHA-ΔNS1 immunized mice had robust antigen-specific CD8+ T-cell responses which also correlated with markedly reduced lung pathology post-challenge. These observations support the development of a trivalent universal influenza vaccine for the protection against group 1 and group 2 influenza A viruses and influenza B viruses.

Fighting flu: novel CD8+ T-cell targets are required for future influenza vaccines

Seasonal influenza viruses continue to cause severe medical and financial complications annually. Although there are many licenced influenza vaccines, there are billions of cases of influenza infection every year, resulting in the death of over half a million individuals. Furthermore, these figures can rise in the event of a pandemic, as seen throughout history, like the 1918 Spanish influenza pandemic (50 million deaths) and the 1968 Hong Kong influenza pandemic (~4 million deaths). In this review, we have summarised many of the currently licenced influenza vaccines available across the world and current vaccines in clinical trials. We then briefly discuss the important role of CD8+ T cells during influenza infection and why future influenza vaccines should consider targeting CD8+ T cells. Finally, we assess the current landscape of known immunogenic CD8+ T-cell epitopes and highlight the knowledge gaps required to be filled for the design of rational future influenza vaccines that incorporate CD8+ T cells.

The race toward a universal influenza vaccine: Front runners and the future directions

Influenza virus is the pathogen of influenza (flu) and millions of people suffer from the infection worldwide, posing a significant health risk. The current influenza vaccines induce neutralizing antibodies against hemagglutinin (HA) to achieve strain-specific neutralization. The effectiveness of seasonal vaccines is usually low and unpredictable because of the antigenic variation and genetic plasticity of viruses, as well as the interference of preexisting immunity. A universal influenza vaccine is urgently needed to prevent a wide variety of influenza viruses. Nevertheless, reaching this difficult optimal goal requires a step-by-step approach. Innovative strategies and vaccine platforms are being developed in order to generate robust cross-protective immunity. In this review, we summarize candidate influenza vaccines that meet two criteria: first, they are designed to provide protection against multiple influenza viruses; second, they had passed regulatory evaluations and have entered various stages of clinical trials. We discuss these vaccine candidates based on the different vaccine-production platforms, with the focus on antigen selection, design, adjuvants, immunomodulators, and routes of vaccine delivery in the development of universal influenza vaccines.

Defective Interfering Particles of Influenza Virus and Their Characteristics, Impacts, and Use in Vaccines and Antiviral Strategies: A Systematic Review

Defective interfering particles (DIPs) are particles containing defective viral genomes (DVGs) generated during viral replication. DIPs have been found in various RNA viruses, especially in influenza viruses. Evidence indicates that DIPs interfere with the replication and encapsulation of wild-type viruses, namely standard viruses (STVs) that contain full-length viral genomes. DIPs may also activate the innate immune response by stimulating interferon synthesis. In this review, the underlying generation mechanisms and characteristics of influenza virus DIPs are summarized. We also discuss the potential impact of DIPs on the immunogenicity of live attenuated influenza vaccines (LAIVs) and development of influenza vaccines based on NS1 gene-defective DIPs. Finally, we review the antiviral strategies based on influenza virus DIPs that have been used against both influenza virus and SARS-CoV-2. This review provides systematic insights into the theory and application of influenza virus DIPs.

Live Influenza Vaccine Provides Early Protection against Homologous and Heterologous Influenza and May Prevent Post-Influenza Pneumococcal Infections in Mice

Influenza and S. pneumoniae infections are a significant cause of morbidity and mortality worldwide. Intranasal live influenza vaccine (LAIV) may prevent influenza-related bacterial complications. The objectives of the study are to estimate resistance against early influenza infection and post-influenza pneumococcal pneumonia after LAIV in mice. Mice were administered intranasally the monovalent LAIV A/17/Mallard Netherlands/00/95(H7N3), A/17/South Africa/2013/01(H1N1)pdm09 or trivalent LAIV 2017–2018 years of formulation containing A/17/New York/15/5364(H1N1)pdm09 vaccine strain. LAIV demonstrated early protection against homologous and heterologous infections with A/South Africa/3626/2013 (H1N1) pdm09 influenza virus on day six, following immunization. Following boost immunization, trivalent LAIV demonstrated a pronounced protective effect both in terms of lethality and pneumococcal lung infection when S. pneumoniae infection was performed three days after the onset of influenza infection. Conclusion: LAIV provides early protection against homologous and heterologous viral infections and has a protective effect against post-influenza pneumococcal infection. These data suggest that the intranasal administration of LAIV may be useful during the cycle of circulation not only of influenza viruses, but also of other causative agents of acute respiratory infections.