A mosaic hemagglutinin-based influenza virus vaccine candidate protects mice from challenge with divergent H3N2 strains

Rescue and characterization of recombinant influenza viruses expressing mosaic hemagglutinin (HA) proteins. a Model of the H3 HA trimer. Residues that were mutated are indicated in color code according to the major antigenic sites. The model is based on the published crystal structure of the HA of A/Victoria/361/2011 (H3N2),47 PDB accession no. 4O5N, and was visualized with the UCSF Chimera software.48 b Amino acid sequences of parts of the major antigenic sites of HK2014 HA (H3 numbering) are aligned with the corresponding sequences of the mosaic mH10/3 and mH14/3 HAs. c Representative scans of HA assays with influenza viruses (allantoic fluids) carrying wild-type (wt), mosaic (mH10/3 and mH14/3), or chimeric (cH10/3 and cH14/3) HAs. d Titers expressed as plaque-forming units per milliliter (PFU/mL) of allantoic fluid of the different influenza viruses. Bars represent the mean？±？SD of nine eggs. e Representative images of MDCK cells infected with the indicated viruses for 16？h obtained by immunofluorescence microscopy. Surface staining with monoclonal antibody 9H10 is shown. The scale bar indicates 100？μm. f HI assays using the indicated viruses and antisera of two ferrets raised against HK2014 virus are shown, with both antisera measured in triplicate