A Panel of Human Monoclonal Antibodies for Tracking the Antigenic Evolution of Influenza H5N1 Clade 2.3.4.4b

Abstract

The ongoing panzootic of clade 2.3.4.4b H5N1 influenza has driven widespread transmission among birds, mammals, and livestock, underscoring the need for tools to interpret its rapid antigenic evolution. Here, we generated and characterized 19 human monoclonal antibodies that potently neutralize clade 2.3.4.4b viruses and collectively recognize five major, partially overlapping antigenic regions of the H5 hemagglutinin. Neutralization profiling and structural analyses revealed distinct patterns of antibody breadth and escape, identifying both clade 2.3.4.4b restricted and broadly neutralizing antibodies targeting conserved surfaces across divergent H5N1 lineages. By incorporating these antibodies into an expanded 32-mAb reference panel, we identified antibody-defined antigenic differences among recent human isolates between cattle-associated B3.13 and poultry-associated D1.1 genotypes. Together, this study establishes a structurally informed, epitope-resolved H5 hemagglutinin antibody reference panel for interpreting emerging HA mutations and monitoring antigenic changes in circulating H5 viruses.