Developing a broadly neutralizing single-domain antibody to the stem domain of hemagglutinin H3 and examining the mechanism of its antiviral activity

The development of universal therapeutic agents for combating influenza is a vital task. Single-domain antibodies (sdAb) represent a promising candidate for the role of a universal antiviral drug. Our objective was to obtain broad-spectrum neutralizing sdAbs binding to conservative hemagglutinin (HA) epitopes of the H3 subtype and to describe their antiviral activity both in vitro and in vivo. Using phage display technology, we isolated three neutralizing sdAbs active against a diverse range of H3 subtype HA and providing 100% protectiveness in vivo. These antibodies were fused with the Fc region of human IgG1 to generate chimeric sdAb-Fc proteins. This fusion enhanced and broadened the spectrum of antiviral activity of the sdAbs. The most promising antibody p2.H5-Fc effectively neutralized various strains of the H3N2 influenza virus and the H7N2 virus. The mechanism of action of p2.H5-Fc has been discovered – it hinders the fusion of viral and endosomal membranes by preventing conformational changes in HA.