New vaccination strategy shows promise in boosting immunity in pigs and curbing influenza spread

Recent PLoS Pathogens Research is evaluated Efficacy A newly developed live attenuated influenza vaccine (LAIV) protocol to elicit immune responses in a swine animal model.

study: Evaluation of a novel intramuscular prime/intranasal boost vaccination strategy against influenza in a swine model. Image credit: ezps / Shutterstock.com

Live attenuated influenza vaccine against influenza virus

LAIV induces a local immune response against several viral antigens. Hemagglutinin (HA), a specific type of immunoglobulin A (IgA) secreted into the respiratory system, blocks the virus's point of entry and prevents it from spreading. Unlike traditional influenza vaccines, LAIV does not require an adjuvant and provides immunity for a longer period of time.

However, a key challenge in LAIV development is proper replication capacity, which can lead to over-attenuation of the virus and hinder its ability to generate a sustained immune response. In comparison, an under-attenuated vaccine Viral shedding The risk of virus entry through the upper respiratory tract and the emergence of more virulent viruses is increased, therefore, it is important to find the right balance between ensuring the safety of this vaccination strategy while achieving sufficient immunogenicity.

About the Study

To date, several LAIVs have been developed, for example, LAIVs based on cold-adapted viruses are recommended for individuals aged 2 to 49 years, and other LAIV strategies use recombinant influenza A viruses (IAVs) containing modified nonstructural 1 (NS1) proteins.

Previously, the authors of this study developed a recombinant LAIV candidate, NS1(1–126), encoding a C-terminally truncated NS1 protein and combined with a mutation in the PA gene (NS1(1–126)-ΔPAX). This modification of the PA gene, which prevents expression of the PA-X protein, improved the safety profile of the NS1(1–126) LAIV candidate.

The recombinant viruses are associated with reduced apoptotic cell death, attenuated viral replication, and improved induction of innate immune responses in porcine bronchiolar epithelial cell lines. This study validates the efficacy of these LAIV candidates by: Alive Pig model.

In the first animal study, 15 healthy 10-week-old pigs were divided into three groups and intranasally infected with wild-type pH1N1/09, pH1N1/09-NS1(1–126), or VSV-Luc as a control.

The second study aimed to evaluate the efficacy of a novel prime/boost immunization protocol. To this end, 25 healthy 10-week-old specific pathogen-free (SPF) mice were first primed intramuscularly with VSV-H1 or control VSV-Luc and then boosted with intranasal immunization of NS1(1–126)-ΔPAX or NS1(1–126) ΔPAX LAIV.

Research findings

NS1(1-126) infection resulted in significantly reduced viral shedding and reduced levels of pH1N1/09-specific antibodies compared with wild-type infection, but virus-specific IgG levels remained similarly high in bronchoalveolar lavage (BAL) samples from both NS1(1-126)- and wild-type-infected pigs.

Animals initially primed with the control vector VSV-Luc and then immunized with NS1-(1-126) ΔPAX showed reduced viral ribonucleic acid (RNA) shedding, whereas no viral shedding was observed in pigs initially primed with VSV-H1 and then boosted 6 days later with NS1(1-126) ΔPAX.

Serum IgG and IgA levels were undetectable after priming with VSV-H1, but strong antibody responses were observed after boosting with NS1(1–126)-ΔPAX or NS1(1–126) LAIV. Serum IgA levels peaked at 2 weeks and then declined rapidly, whereas serum IgG levels plateaued 2 weeks after the boost and then declined slowly.

Primary vaccination with VSV-H1 did not produce high levels of virus.Neutralizing antibodiesHowever, boosting with NS1(1–126)-ΔPAX or NS1(1–126)LAIV induced significant increases in virus-neutralizing antibodies and CD4 counts.⁺ T cells.

CD4⁺ T cells expressed tumor necrosis factor (TNF) and interferon-γ (IFNγ) independently or simultaneously, but not interleukin-17 (IL-17), and these effects were not seen in pigs immunized with control VSV-Luc and subsequently boosted with NS1(1–126)-ΔPAX.

After the booster vaccination, pigs were inoculated intranasally with pH1N1/09 ​​to confirm the efficacy of this vaccination protocol against infection. No viral RNA was detected in nasal samples from the VSV-H1/NS1(1-126) ΔPAX, VSV-H1/NS1(1-126), and VSV-Luc/NS1(1-126)- ΔPAX groups.

Conclusion

Study results suggest that the proposed vaccine protocol induced systemic IAV-specific immunity in terms of enhanced memory Th1 cells, IgG, and neutralizing antibody titers.Primary vaccination with VSV-H1 followed by booster vaccination with NS1(1–126)-ΔPAX LAIV significantly reduced LAIV shedding and completely prevented challenge virus shedding, enhancing safety.

The novel prime/boost vaccination protocol established in this study may support the future development of next-generation vaccination strategies to more effectively manage seasonal influenza epidemics. Mucosal immunity generated by this approach may improve herd immunity, mitigate IAV spread, and control future IAV epidemics, as this strategy can be easily adapted and timed to emerging IAV subtypes.