Construction of an mRNA vaccine encoding hemagglutinin of influenza A H1N1 virus and investigation on booster immunization strategy

Objective·To construct an mRNA vaccine encoding hemagglutinin (HA) of influenza A H1N1 virus, and explore the protective effects of different booster vaccination strategies.Methods·Firefly luciferase (Fluc) was used as the reporter gene to construct Fluc mRNA vaccine enveloped in lipid nanoparticles (LNP). The in vivo expression of Fluc mRNA-LNP after intramuscular injection was determined by live imaging assay in mice. Furthermore, M15-HA mRNA-LNP derived from H1N1 subtype (A/Michigan/45/2015) was constructed. Mice were immunized with 20, 10, 5, or 1 µg doses of M15-HA mRNA-LNP twice (with an interval of 3 weeks) through intramuscular injection. Serum antibody titers were measured by enzyme-linked immunosorbent assay (ELISA) at 2 weeks and 4 weeks after the second immunization, and functional antibody levels were detected by hemagglutination inhibition test. The third booster vaccination was performed 40 d after the second immunization in 1 µg dose group with 1 µg M15-HA mRNA-LNP or 10 µg HA subunit vaccine.