Immune response against DNA- and mRNA vaccines encoding artificial influenza virus immunogens

Constant antigenic drift of circulating influenza viruses leads to inefficiency of seasonal influenza vaccines, thus requiring annual re-design of these vaccines. Therefore, the development of a universal influenza vaccine is of particular relevance. A promising line of research in this area is to design the immunogens consisting of conserved protein fragments from different influenza viral strains. The aim of this work was to assess immunogenicity of DNA vaccines and mRNA vaccines encoding artificial antigens consisting of conserved hemagglutinin stem fragments and conserved M2 protein. We have obtained DNA vaccine constructs encoding artificial immunogens AgH1, AgH3, and AgM2, which contained conserved fragments of the hemagglutinin stalk from the two subtypes of influenza A – H1N1 and H3N2, and conserved M2 protein. These DNA vaccines were used as templates for the synthesis of mRNA vaccines. To assess immunogenicity of the obtained constructs, BALB/c mice were immunized with DNA and mRNA vaccines by i/m administration. Assessment of the humoral immune response was carried out by ELISA, using influenza viruses A/Aichi/2/68(H3N2), A/California/07/2009 as antigens and the ULTRIX vaccine containing purified antigens of H1N1 and H3N2 influenza viruses. T cell immune response was assessed using two methods: intracellular cytokine staining (ICS) and ELISpot. ICS was performed to determine CD8⁺ and CD4⁺T-lymphocytes producing IFNγ. ELISpot was carried out using the mouse IFNγ ELISpot kit (BD). A peptide mixture which included composition of the target antigens, was used for cell stimulation. The results showed that the designed DNA vaccine constructs induce virus-specific humoral and cellular responses in immunized BALB/c mice. Intramuscular administration of the naked mRNA vaccine constructs induced a weak humoral immune response, thus suggesting a need for further work to improve the delivery approaches.