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Currently, influenza vaccines are produced using embryonated chicken eggs. Recently, recombinant influenza vaccines have been developed as a potential alternative to egg-grown vaccines. In this study, we evaluated the efficacy of soluble recombinant hemagglutinin (HA) protein produced in human cell culture (Expi293F cells) as an influenza vaccine against homosubtypic and heterosubtypic influenza virus challenges in mice. Mice were immunized intramuscularly with purified soluble HA protein of H1N1pdm09 virus and then challenged with a lethal dose of H1N1pdm09, seasonal H3N2, or highly pathogenic avian influenza (HPAI) H5N1 virus. Vaccinated mice showed better morbidity than mock-vaccinated mice following H1N1pdm09 challenge. By contrast, all mice died following H3N2 challenge. Interestingly, all vaccinated mice survived challenge with H5N1 virus, whereas all mock-vaccinated mice died. These results suggest that intramuscular immunization with recombinant HA proteins produced in Expi 293F cells could be of value in influenza vaccine strategies. [ABSTRACT FROM AUTHOR]

Many cases of human infection with the H7N9 virus have been detected in China since 2013. H7N9 viruses are maintained in chickens and are transmitted to humans at live bird markets. During circulation in birds, H7N9 viruses have accumulated amino acid substitutions in their hemagglutinin (HA), which resulted in an antigenically change in the recent H7N9 viruses. Here, we characterized 46 mouse monoclonal antibodies against the HA of the prototype strain. 16 H7-HA-specific monoclonal antibodies (mAbs) possessed hemagglutination inhibition (HI) and neutralization activities by recognizing the major antigenic site A; four other H7-HA-specific clones also showed HI and neutralizing activities via recognition of the major antigenic sites A and D; seven mAbs that reacted with several HA subtypes and possibly recognized the HA stem partially protected mice from lethal infection with prototype H7N9 virus; and the remaining 19 mAbs had neither HI nor neutralization activity. All human H7N9 viruses tested showed a similar neutralization sensitivity to the first group of 16 mAbs, whereas human H7N9 viruses isolated in 2016–2017 were not neutralized by a second group of 4 mAbs. These results suggest that amino acid substitutions at the epitope of the second mAb group appear to be involved in the antigenic drift of the H7N9 viruses. Further analysis is required to fully understand the antigenic change in H7N9 viruses. [ABSTRACT FROM AUTHOR]