Adaptation of H2N2 influenza viruses with different receptor specificity to MDCK cells: opportunities for the development of a cell-based vaccine against pandemic H2N2 influenza

Abstract

Introduction. H2N2 influenza viruses caused a pandemic in 1957 due to the adaptation of avian influenza hemagglutinin from avian-type α2,3 to human-type α2,6 receptor specificity. These viruses have not circulated among humans for more than 50 years but are still found in avian reservoirs, indicating their pandemic potential. It is known that at the beginning of a pandemic wave, viruses with α2,3 and α2,6 receptor specificities can co-circulate, and the selection of one or another isolate for the development of a better pandemic influenza vaccine should be based on strong scientific evidence. Although the vast majority of influenza vaccines are produced in chicken embryos, mammalian cell culture may be a preferred substrate for the production of pandemic influenza vaccines. Materials and methods. In this study, we investigated two variants of A/Singapore/1/57 (H2N2) virus which differed by their receptor specificity defined by three residues in the HA1 molecule: E156, Q226, G228 for α2,3 avian-type (Sing-α2,3) and K156, L226, S228 for α2,6 human-type (Sing-α2,6) receptor specificity. We conducted serial passaging of these viruses on MDCK cells and analyzed growth properties of plaque-purified clones in vitro and in vivo, as well as their immunogenicity and cross-reactivity in a mouse model. Results. Adaptation to MDCK cells significantly increased viral titers in MDCK cells; however, their receptor specificity was not affected. Viruses with α2,6 receptor specificity induced higher titers of homologous antibodies compared to the viruses with α2,3 receptor specificity, but these antibodies could react only with the α2,6 viruses. In contrast, antibody induced by viruses with α2,3 receptor specificity had broad reactivity against all studied viruses. Similar results were obtained for the pair of A/Leningrad/17-based H2N2 live attenuated influenza vaccines with α2,3 and α2,6 receptor specificities in experiments on Syrian hamsters. Conclusion. In the case of a new transmission of H2N2 avian influenza viruses to the human population and co-circulation of viruses with both receptor specificities, the variant with α2,3 specificity should be selected for the development of cross-reactive influenza vaccines.

Keywords

• influenza virus
• h2n2
• receptor specificity
• adaptation
• mdck cells
• live attenuated influenza vaccine
• immunogenicity