Identification of broad-spectrum neutralizing antibodies against influenza A virus and evaluation of their prophylactic efficacy in mice.

Influenza A virus continuously infects humans and the antigenic shifts of this respiratory virus enable it to cross the species barrier, threatening public health with the risk of pandemics. Broadly neutralizing antibodies (bnAbs) that target the antigenic surface glycoprotein, hemagglutinin (HA), of influenza A virus protect against various subtypes of the virus. Here, we screened a human scFv library, through phage display and panning against recombinant HA proteins, to discover human monoclonal antibodies (mAbs) that are broadly active. Consequently, two human mAbs, named G1 and G2, were identified, which target the HA proteins of the H1N1 and H3N2 subtypes, respectively. G1 was shown to have broad binding ability to different HA subtypes of group 1. By contrast, G2 had higher binding affinity but sensed exclusively H3 subtype-derived HAs. In a cell culture-based virus-neutralizing assay, both G1 and G2 efficiently suppressed infection of the parental influenza A viruses of H1N1 and H3N2 subtypes. Mode-of-action studies showed that the G1 antibody blocked HA2-mediated membrane fusion. Meanwhile, G2 inhibited HA1-mediated viral attachment to host cells. It is noteworthy that both antibodies elicited antibody-dependent cellular cytotoxicity (ADCC) activities by recruiting FcγRIIIA-expressing effector cells. In mouse challenge models, single-shot, intraperitoneal administration of chimeric G1 and G2 antibodies with the mouse IgG constant region completely protected mice from viral infections at doses above 10 and 1 mg/kg, respectively. The newly identified bnAbs, G1 and G2, could provide insight into the development of broad-spectrum antivirals against future pandemic influenza A virus involving group 1- or H3-subtyped strains. • Human monoclonal antibodies, G1 and G2, specific for influenza A virus HA have been generated from a human scFv library. • G1 binds to the HA2 stem of group 1 influenza A viruses, while G2 targets the HA1 subunit of H3 subtype viruses. • G1 and G2 neutralize human influenza A viruses of the H1N1 and H3N2 subtypes in vitro , respectively. • These two antibodies elicit antibody-dependent cellular cytotoxicity by recruiting FcγRIIIA-expressing effector cells. • G1 and G2 protect mice against lethal challenge with influenza A viruses, H1N1 and H3N2, respectively. [ABSTRACT FROM AUTHOR]