Abstract
Vaccination is one of the most effective interventions for preventing the spread of influenza viruses at the population level. Currently most influenza vaccines are produced by using embryonated chicken eggs, but alternative methods that achieve more rapid large-scale production are highly desirable for vaccines against both pandemic and seasonal influenza viruses. The use of recombinant hemagglutinin (HA), a key virus surface protein, as an antigen is an attractive candidate alternative approach, because of the potential for high protein yields and the ease of cloning new antigenic variants. Although fusion of HA with trimerization domains is needed to stabilize the trimeric structure and enhance the immunogenicity of the recombinant HA protein, whether the trimerization domains are immunogenic must be considered. Here, we generated recombinant multimeric HA without trimerization domains by using a short peptide linker, termed a single-chain HA (scHA), and evaluated scHAs as potential antigens for generating vaccines against influenza virus. Using mammalian cells, we succeeded in making three types of recombinant scHAs—two dimeric scHAs and a trimeric scHA. After immunization with aluminium salts in mice, one of the dimeric scHAs induced the greatest HA-specific IgG response among the scHAs and protected against virus challenge as strongly as the typically used trimeric HA containing a trimerization domain. We did not observe IgGs specific for the short peptide linker in mice immunized with the dimeric scHA, although IgGs specific for the trimerization domain occurred in mice immunized with the trimeric HA containing that domain. Furthermore, changing to another adjuvant did not diminish the utility of the dimeric scHA. These results suggest the potential usefulness of dimeric scHA as a vaccine antigen. We believe that single-chain antigens may represent new alternatives for production of recombinant antigen–based vaccines.
Highlights
Influenza A viruses remain a serious public health threat worldwide
We used the ectodomain of HA from H1N1 influenza A viruses for generating the recombinant HA, and a hexahistidine tag (His-tag) was introduced at the C-terminus to facilitate purification
In size-exclusion chromatography, HA-foldon and triscHA eluted at almost the same volume that was expected from their anticipated molecular weight (Figure 1b); in contrast, the elution times of mono-HA, di-single-chain HA (scHA)-L1, and di-scHA-L2 were longer than those of HAfoldon and tri-scHA (Figure 1b), and the elution times of di-scHA-L1
Summary
Influenza A viruses remain a serious public health threat worldwide. According to the World Health Organization (https://www.wh o.int/en/news-room/fact-sheets/detail/influenza-(seasonal)), seasonal influenza viruses cause approximately 290,000–650,000 deaths annually worldwide, in young and elderly people. Almost all current influenza vaccines confer potent protection against antigenically matched or closely related homologous viruses infections by inducing strain-specific antibodies to key virus surface proteins, such as hemagglutinin (HA) [1]. These strain-specific antibodies cannot protect against antigenically drifted heterologous viruses, due to mutation of the HA receptor-binding site [2, 3]. In addition to seasonal heterologous strains, pandemic strains such as the antigenically divergent H5N1 and H7N9 avian influenza viruses are extremely worrisome from a public health standpoint, because of the ineffectiveness of seasonal vaccines against these pandemic strains. Avian-to-human transmission of H7N9 influenza virus in China led to several hundred cases of flu in humans, with a case fatality rate of approximately 40% [6]
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