Human monoclonal antibodies that target clade 2.3.4.4b H5N1 hemagglutinin
The highly pathogenic avian influenza H5N1 virus clade 2.3.4.4b has been spreading globally since 2022, causing mortality and morbidity in domestic and wild birds and mammals, including infection in humans, raising concerns about its pandemic potential. We aimed to generate a panel of anti-hemagglutinin (HA) human monoclonal antibodies (mAbs) against the H5 protein of clade 2.3.4.4b. H2L2 Harbour Mice(R), which express human immunoglobulin germline genes, were immunized with H5 and N1 recombinant proteins from A/mallard/New York/22-008760-007-original/2022 H5N1 virus, enabling the generation of human chimeric antibodies. Through hybridoma technology, sixteen full human mAbs were generated, most of which showed cross-reactivity against H5 proteins from different virus variants. The functionality of the sixteen mAbs was assessed in vitro using hemagglutination inhibition and microneutralization assays with viruses containing a clade 2.3.4.4b HA. Fourteen out of the sixteen mAbs neutralized the virus in vitro. The mAbs with the strongest hemagglutination inhibition activity also demonstrated greater neutralizing capacity and showed increased protective effects in vivo when administered prophylactically or therapeutically in a murine H5N1 challenge model. Using cryo-electron microscopy, we identified a cross-clonotype conserved motif that bound a hydrophobic groove on the head domain of H5 HA. Akin to mAbs against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) during the coronavirus 2019 (COVID-19) pandemic, these mAbs could serve as important treatments in case of a widespread H5N1 epidemic or pandemic.