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

Henning Jacobsen,Angela Choi,Madhusudan Rajendran,Haakon Sjursen,Karl A Brokstad,Rebecca J Cox,Florian Krammer,Raffael Nachbagauer,Peter Palese,Rino Rappuoli

doi:10.1128/mbio.01463-17

Abstract

ABSTRACTThe 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.

Highlights

IMPORTANCE Influenza viruses are a serious concern for public health and cause a large number of deaths worldwide every year
Recent advances in influenza virus vaccine research have enabled the development of novel vaccination strategies that target highly conserved epitopes in the influenza hemagglutinin stalk domain
We had previously shown that vaccination with vaccines based on avian subtypes that contain an exotic HA head domain and an HA stalk domain that is similar to that of circulating influenza viruses can potently induce stalk-reactive antibodies in humans [21]

Summary

Introduction

IMPORTANCE Influenza viruses are a serious concern for public health and cause a large number of deaths worldwide every year. HAI titers of 1:40 have been shown to correlate with a 50% reduction in infection and are commonly used as an indicator for successful seroconversion in influenza virus vaccination trials [5,6,7] This protective titer was originally established in healthy adults with specific virus strains and does not necessarily apply to all age groups or to all influenza viruses. Recent advances in influenza virus research have resulted in novel candidate vaccines that are aimed at inducing broader protection from influenza virus infection Some of these approaches focus on shifting the antibody response away from the HA head domain and toward the conserved HA stalk region. To see if in vitro binding and functional assays correlate with protection in vivo, we tested human serum samples from two influenza virus vaccination trials in multiple assays and correlated the results with weight loss in a serum transfer mouse challenge model

Methods

Results

Conclusion