A new H9 influenza virus mRNA vaccine elicits robust protective immunity against infection.

Avian influenza virus (AIV) poses a great threat to the poultry industry and public health. However commercial vaccines only provide limited immunity due to rapid virus mutation and rearrangement. Here, we developed an mRNA-lipid nanoparticle (mRNA-LNP) vaccine expressing AIV immunogenic protein hemagglutinin (HA) and also assessed its safety and immune-protection efficacy in vivo. Specifically, its safety was tested by inoculation of SPF chicken embryos and chicks, and there showed no clinical manifestations and pathological changes in both. As for the immune efficacy, the antibody titers, IFN-γ production levels, and viral loads in various organs were analyzed. The results showed that chickens in the mRNA-LNP-inoculated groups produced higher specific antibody titers compared with that in the control group by hemagglutination inhibition (HI) test. Meanwhile, the ELISpot assay demonstrated that the expression of IFN-γ was markedly induced in the mRNA-LNP group, and the viral loads in multiple organs were decreased. In addition, HE shows no obvious pathomorphological changes in the lungs of the mRNA-LNP-inoculated group. While, there was severe inflammatory cell infiltration in the DMEM-treated group instead. Taken together, the vaccine prepared in this study was safe and could trigger potent cellular and humoral immune response to defend against virus infection.