Characterization of the Human Antibody Response to the Influenza A Virus Neuraminidase Glycoprotein

Abstract

Influenza is an acute viral respiratory disease that remains a major public health burden, causing annual epidemics and occasional pandemics with significant illness and death. This work describes the discovery of monoclonal antibodies (mAbs) targeting the neuraminidase (NA) glycoprotein of type A influenza viruses (IAVs) from individuals with extensive influenza exposure histories that show antiviral activity and can guide the design of future vaccines. We first describe a clonal B cell lineage targeting the IAV NA active site and identify two candidate mAbs that inhibit the enzymatic activity of three NA subtypes and provide protection in vitro and in vivo. Phylogenetic analysis of this lineage showed that B cells gained cross-reactivity after repeated antigen exposures, suggesting that even mono-reactive naïve B cells can be trained to produce broadly neutralizing antibodies with the right immunogen. These findings offer insights into using reverse vaccinology to find conserved epitopes across IAV NA subtypes, which can be used to generate long-lasting, cross-protective immunity through vaccination. In response to an emerging bovine IAV H5N1, we isolated bovine N1-reactive mAbs from memory B cells of two influenza-experienced donors. These antibodies bind epitopes conserved between human-, avian-, and bovine-derived N1 strains that are away from the NA active site and prevent enzymatic activity through steric hindrance. Furthermore, these mAbs reduced cell-to-cell spread of a human H1N1 virus strain and provided protection against lethal challenge with human H1N1 and avian H5N1 viruses. These results suggest that pre-existing immunity to the emerging influenza strain may already exist in the population and highlight non-active site epitopes as potential sites of vulnerability. NA-inhibiting mAbs such as those described here can be used as antiviral treatments and to study humoral responses to vaccination and natural infection. Our findings emphasize the importance of future long-term studies to track how exposure influences the NA-mediated antibody response and support the evaluation and standardization of NA in next-generation vaccine designs.