Preparation and characteristic analysis of six influenza A (H7N9) pseudovirus derived from different districts of China

Objective To prepare strains of influenza A (H7N9) pseudovirus derived from different districts of China for vaccine efficacy evaluation. Methods Phylogenetic tree was built based on hemagglutinin (HA) amino acid sequence analyses from 29 influenza A (H7N9) virus strains and 6 influenza A (H7N9) virus strains with HA determinants variation were selected. 293FT cells were co-transfected with plasmid pNL4-3-Luc.R-E-, pVRC-HA and pVRC-NA with codon-optimized hemagglutinin (HA) and neuraminidase (NA) derived from the six influenza A (H7N9) virus strains, respectively. Transmission electron microscopy assay and Western blot analysis were performed to demonstrate morphology and specificity of these particles, luciferase activity assay and hemagglutinin titers detection were used to determine their infectivity and hemagglutinin activity. And finally, pseudovirus-based neutralization assays were evaluated with HA immunized mice serum. Results Six influenza A (H7N9) peseudovirus particles derived from different districts of China were selected and prepared. All of the particles bearing HA and NA were characterized with classic influenza virus morphology, with TCID50 titer ranged from 104TCID50/50 μl to 105TCID50/50 μl and with hemagglutinin activity ranged from 64 to 512. Neutralization efficacies on influenza A/Shanghai/1/2013(H7N9) HA vaccine serum against 100TCID50 dose of these pseudovirus particles indicated their potential application in the vaccine cross-protective evaluation in future. Conclusions Six influenza A (H7N9) pseudovirus derived from different districts of China with potential antigenic variation on HA were constructed successfully, established foundation for their further application in vaccine cross-reactive efficacy evaluation. Key words: Influenza A (H7N9) virus; Pseudovirus; Hemagglutinin; Antigenic variation; Neutralization