Abstract
English Abstract Highly pathogenic avian influenza H5N1 viruses can result in poultry and occasionally in human mortality. The inherent nature of antigenic changes in influenza viruses has not been sufficiently taken into account in immunogen designs for broadly protective HPAI H5N1 vaccines. Hemagglutinin (HA), a major envelope protein accounting for approximately 80% of spikes in influenza virus, is often used as a major antigen for subunit vaccine development. In this study, we investigated the recombinant HA protein immunogenicity in mice, and found that the combined use of the recombinant HA protein with the recombinant adenovirus encoding HA improved the antibody responses against homologous and heterologous H5N1 virus strains. Using this immunization regimen, the glycan-masking g127+g138 double mutant was demonstrated to elicit significantly broader hemagglutination inhibition and neutralizing antibody responses against heterologous H5N1 virus strains by increasing more RBS-specific and stem-specific antibodies. Finally, the recombinant HA containing complex terminally sialylated and asialyated-galactose type N-glycans were found to induce higher levels of functional antibodies and better protective immunity. The results are highly relevant to issues that should be considered in the development of broadly protective H5N1 vaccines.