Background

Avian Influenza Virus (AIV) is a representative pathogen threatening the global poultry industry and food security. Frequent mutations between various subtypes and the risk of interspecies transmission are major obstacles to disease control. In existing poultry farms, inactivated vaccines or virus vector-based vaccines have been primarily used to induce herd immunity. These traditional vaccine platforms have shown structural limitations in forming long-lasting immunity and have limited cross-protective capabilities against AIV variants with high genetic diversity. Because antibody responses induced by the surface antigen hemagglutinin (HA) tend to be biased toward specific antigenic types, the problem of rapidly declining protective efficacy whenever new variants emerge has recurred. Consequently, there has been a continuous demand to develop next-generation preventive measures capable of responding broadly to various variants by applying delivery technologies that proved rapidness and scalability during the COVID-19 pandemic to poultry vaccines.

Key Findings

Researchers in India focused on the Matrix Protein 2 Ectodomain (M2e), a highly conserved sequence across Influenza A viruses. Because M2e has inherently low immunogenicity, the research team designed a 4xM2e structure consisting of four consecutive repeats of this protein sequence. To maximize antigen peptide delivery efficiency and T-cell activity, they constructed a complex sequence fusing the chicken Major Histocompatibility Complex II (MHC-II) Invariant chain (Ii) motif with a 13-amino acid Pan-DR-binding epitope (PADRE). The completed genetic material was loaded into standard Lipid Nanoparticles (LNPs), and vaccine efficacy was evaluated via two routes: intramuscular injection and intranasal administration.

As a result of administration, significant systemic and mucosal antibody responses were induced in experimental birds, along with increased T-cell proliferation and elevated proportions of CD4+ and gamma-delta (γδ) T-cell fractions. Subsequently, when a challenge infection experiment was performed with the field isolate A/turkey/Wisconsin/1/1966 (H9N2) virus, viral shedding was significantly reduced in both the intramuscular and intranasal administration groups. In lung tissue pathological analysis, the bronchial and alveolar structures were maintained intact, and inflammatory cell infiltration was minimized, proving the integrity of the respiratory mucosal barrier. Through in vitro experiments, the researchers confirmed that the induced anti-M2e antibodies also recognize the heterologous subtype PR8 (H1N1) virus and identified Antibody-Dependent Cellular Cytotoxicity (ADCC) functions that selectively eliminate infected cells.

Significance and Outlook

This study experimentally demonstrated that combining optimized conserved antigen design with LNP delivery technology can protect against multiple subtypes of avian influenza with a single vaccine. In particular, the respiratory mucosal immune induction effect confirmed via intranasal administration opens the possibility for developing spray-type mass vaccination technology in large-scale poultry environments in the future. Another major advantage is that even if new variants emerge, candidate materials can be produced in a short period through nucleotide sequence redesign. However, for implementation in actual livestock operations, improvements to the cold chain system requiring sub-zero storage and a reduction in production costs compared to commercial inactivated vaccines remain prerequisite challenges. It is anticipated that the transition to the commercialization stage will require additional formulation research to extend the duration of immunity in long-term rearing groups such as layers and breeders, as well as verification of protective efficacy against highly pathogenic H5-lineage viruses.