Nucleoside-modified mRNA-based influenza vaccines circumvent problems associated with H3N2 vaccine strain egg-adaptation

Most human influenza vaccine antigens are produced in fertilized chicken eggs. Recent H3N2 egg-based vaccine antigens have limited effectiveness, partially due to egg-adaptive substitutions that alter the antigenicity of the hemagglutinin (HA) protein. The nucleoside-modified messenger RNA encapsulated in lipid nanoparticle (mRNA-LNP) vaccine platform is a promising alternative for egg-based influenza vaccines because mRNA-LNP-derived antigens are not subject to adaptive pressures that arise during the production of antigens in chicken eggs. Here, we compared H3N2-specific antibody responses in mice vaccinated with either 3c.2A H3-encoded mRNA-LNP or a conventional egg-based Fluzone vaccine (which included an egg-adapted 3c.2A antigen) supplemented with an MF59-like adjuvant. We tested mRNA-LNP encoding wild-type and egg-adapted 3c.2A H3 antigens. We found that mRNA-LNP encoding wild-type 3c.2A H3 elicited antibodies that neutralized the wild-type 3c.2A H3N2 virus more effectively relative to antibodies elicited by mRNA-LNP encoding egg-adapted 3c2.A H3 or the egg-based Fluzone vaccine. mRNA-LNP expressing either wild-type or egg-adapted 3c2.A H3 protected mice against infection with the wild-type 3c2.A H3N2, whereas the egg-based Fluzone vaccine did not. We found that both mRNA-LNP vaccines elicited high levels of group 2 HA stalk-reactive antibodies that likely contributed to protection in vivo . Our studies indicate that nucleoside-modified mRNA-LNP-based vaccines can circumvent problems associated with egg-adaptations with recent 3c2.A H3N2 viruses. Summary This study shows that the nucleoside-modified messenger RNA encapsulated in lipid nanoparticle (mRNA-LNP) vaccine platform is a promising alternative for egg-based influenza vaccines. We show that mRNA-LNP expressing H3 antigens elicit high levels of antibodies in mice and protect against H3N2 influenza virus infection.