Am80-LNP mRNA vaccines induce respiratory mucosal immunity and confer protection against influenza A and B virus challenge in mice

Seasonal influenza causes a significant global disease burden every year. Currently licensed injectable influenza vaccines mainly elicit humoral immune responses with minimal mucosal immunity in the respiratory tract, limiting their ability to block viral infection and transmission. Messenger RNA (mRNA) vaccines formulated with lipid nanoparticles (LNPs) offer rapid design and flexibility and are highly immunogenic, yet share this limitation of mucosal immunity. Here, we developed influenza A and B mRNA vaccines (Am80-LNP/IFA and Am80-LNP/IFB) using Am80-loaded LNP (Am80-LNP) encoding viral hemagglutinin (HA). Intramuscular immunization of mice with Am80-LNP/IFB (encoding influenza B/Victoria HA) at 1 and 10 μg doses induced systemic HA-specific IgG responses comparable to those elicited by a commercial LNP formulation (SM102-LNP/IFB) and a licensed split vaccine. Notably, Am80-LNP/IFB markedly enhanced respiratory mucosal immunity, inducing 5.4-fold (1 μg) and 11.8 -fold (10 μg) higher virus-specific IgA in bronchoalveolar lavage fluid relative to SM102-LNP. In addition, Am80-LNP/IFB-10 increased lung CD4⁺ tissue-resident memory T (T RM ) cells by 1.4-fold. Following lethal challenge of the influenza B virus, all mRNA-LNP/IFB vaccinated mice survived without weight loss, whereas the split-vaccinated mice experienced a transient decline to 88% of their initial body weight. Am80-LNP/IFB significantly reduced viral loads, rendering viral RNA undetectable in the lungs and nasal turbinates by 14 days post-infection (dpi) at a 10 μg dose. In addition, the Am80-LNP/IFA vaccine (encoding A/H1N1 HA) achieved complete viral clearance in nasal turbinates by 3 dpi, outperforming the split vaccine. These findings indicate that Am80-LNP enables injectable influenza mRNA vaccines to induce robust systemic immunity together with potent respiratory mucosal IgA and T RM responses, overcoming a major limitation of current inactivated vaccines.