Influenza Virus Hemagglutinin Stalk-Specific Antibodies in Human Serum are a Surrogate Marker for In Vivo Protection in a Serum Transfer Mouse Challenge Model

Abstract

The immunogenicity of current influenza virus vaccines is assessed by measuring an increase of influenza virus-specific antibodies in a hemagglutination inhibition assay. This method exclusively measures antibodies against the hemagglutinin head domain. While this domain is immunodominant, it has been shown that hemagglutination inhibition titers do not always accurately predict protection from disease. In addition, several novel influenza virus vaccines that are currently under development do not target the hemagglutinin head domain, but rather more conserved sites, including the hemagglutinin stalk. Importantly, antibodies against the hemagglutinin stalk do not show activity in hemagglutination inhibition assays and will require different methods for quantification. In this study, we tested human serum samples from a seasonal influenza virus vaccination trial and an avian H5N1 virus vaccination trial for antibody activities in multiple types of assays, including binding assays and also functional assays. We then performed serum transfer experiments in mice which then received an H1N1 virus challenge to assess the in vivo protective effects of the antibodies. We found that hemagglutinin-specific antibody levels measured in an enzyme-linked immunosorbent assay (ELISA) correlated well with protection from weight loss in mice. In addition, we found that weight loss was also inversely correlated with the level of serum antibody-dependent cellular cytotoxicity (ADCC) as measured in a reporter assay. These findings indicate that protection is in part conferred by Fc-dependent mechanisms. In conclusion, ELISAs can be used to measure hemagglutinin-specific antibody levels that could serve as a surrogate marker of protection for universal influenza virus vaccines.

Comparison of hemagglutination inhibition, single radial hemolysis, virus neutralization assays, and ELISA to detect antibody levels against seasonal influenza viruses

“…Although ELISA is not officially recognized by the EMA, the technique is able to measure different class‐specific IgM, IgA, and IgG antibodies. In addition, the assay is able to measure HA stalk‐specific antibodies and could be used to evaluate the immunogenicity of novel universal influenza vaccines . ELISA is particularly suitable for large‐scale serological investigation, as it yields unbiased results in a few hours and allows complete automation of the process by high‐throughput testing.…”

“…In addition, the assay is able to measure HA stalkspecific antibodies and could be used to evaluate the immunogenicity of novel universal influenza vaccines. 34 ELISA is particularly suitable for large-scale serological investigation, as it yields unbiased results in a few hours and allows complete automation of the process by high-throughput testing. Our data reveal a positive correlation between ELISA and the other three assays, with lower values for A strains but without differences between A and B strains.…”

Meeting report and review: Immunological assays and correlates of protection for next‐generation influenza vaccines

“…However, an advantage is that different conditions, like obesity, immune senescence, immunosuppression, pregnancy, can be tested in these models—something that cannot be done easily in humans, for example in CHIVIMs. Another interesting possibility for identifying correlates of protection in animal models is to transfer human serum into animals and determine which markers in the human serum correlate with protection of the animal from challenge …”

“…Another interesting possibility for identifying correlates of protection in animal models is to transfer human serum into animals and determine which markers in the human serum correlate with protection of the animal from challenge. 61…”

Assessing the protective potential of H1N1 influenza virus hemagglutinin head and stalk antibodies in humans

“…Both the prophylactic passive transfer of a human anti-HA stalk mAb or the elicitation of HA stalk-specific Abs by chimeric HA vaccination decreased viral loads in ferrets following pH1N1 infection (25). Additionally, passive transfer of human sera from H5N1 vaccinees protects mice from lethal pH1N1 infection (26), and this protection is likely mediated by HA stalk Abs. Passive transfer of broadly neutralizing HA stalk-specific mAbs against group 2 influenza A viruses also protects mice against heterosubtypic H3 viruses (29) and heterologous H3 and H7 viruses (14).…”