Characterization of a Broadly Neutralizing Monoclonal Antibody That Targets the Fusion Domain of Group 2 Influenza A Virus Hemagglutinin

Abstract

Due to continuous changes to its antigenic regions, influenza viruses can evade immune detection and cause a significant amount of morbidity and mortality around the world. Influenza vaccinations can protect against disease but must be annually reformulated to match the current circulating strains. In the development of a broad-spectrum influenza vaccine, the elucidation of conserved epitopes is paramount. To this end, we designed an immunization strategy in mice to boost the humoral response against conserved regions of the hemagglutinin (HA) glycoprotein. Of note, generation and identification of broadly neutralizing antibodies that target group 2 HAs are rare and thus far have yielded only a few monoclonal antibodies (MAbs). Here, we demonstrate that mouse MAb 9H10 has broad and potent in vitro neutralizing activity against H3 and H10 group 2 influenza A subtypes. In the mouse model, MAb 9H10 protects mice against two divergent mouse-adapted H3N2 strains, in both pre-and postexposure administration regimens. In vitro and cell-free assays suggest that MAb 9H10 inhibits viral replication by blocking HA-dependent fusion of the viral and endosomal membranes early in the replication cycle and by disrupting viral particle egress in the late stage of infection. Interestingly, electron microscopy reconstructions of MAb 9H10 bound to the HA reveal that it binds a similar binding footprint to MAbs CR8020 and CR8043. IMPORTANCEThe influenza hemagglutinin is the major antigenic target of the humoral immune response. However, due to continuous antigenic changes that occur on the surface of this glycoprotein, influenza viruses can escape the immune system and cause significant disease to the host. Toward the development of broad-spectrum therapeutics and vaccines against influenza virus, elucidation of conserved regions of influenza viruses is crucial. Thus, defining these types of epitopes through the generation and characterization of broadly neutralizing monoclonal antibodies (MAbs) can greatly assist others in highlighting conserved regions of hemagglutinin. Here, we demonstrate that MAb 9H10 that targets the hemagglutinin stalk has broadly neutralizing activity against group 2 influenza A viruses in vitro and in vivo.

Preexisting human antibodies neutralize recently emerged H7N9 influenza strains

“…These studies emphasize the importance of receiving the annual influenza vaccine for protection against current circulating human influenza strains and future strains with pandemic potential. Identification of broadly neutralizing monoclonal antibodies is of major interest for therapeutic approaches, and many antibodies with conserved epitopes have been isolated from mice and humans (16,19,22,33,(36)(37)(38)(39). These various antibodies and the 3 H7N9-neutralizing antibodies reported here may prove useful to treat infections with emerging and pathogenic influenza strains.…”

Epitope specificity plays a critical role in regulating antibody-dependent cell-mediated cytotoxicity against influenza A virus

“…After antibodies were added to the HA-expressing cells, a luciferase reporter cell line expressing murine FcγRIV was added to wells to allow for the quantification of ADCC induction. Cells infected with IAV strain X-31 (H3N2) were incubated with the murine HA stalk-binding bnAb 9H10 (IgG2a) (24) or the H3 head domain neutralizing antibody XY102 (IgG2a) (25) at concentrations ranging from 0.0008 to 5 μg/mL. As expected, 9H10 potently induced ADCC, whereas XY102 did not.…”

Masking of antigenic epitopes by antibodies shapes the humoral immune response to influenza

“…Observations of OAS are based on measurements with the haemagglutination inhibition (HAI) assay [30,31,35] which quantify antibodies to the head of HA but not to the stem [6,36]. In this paper, we consider OAS following sequential immunizations with two strains of influenza.…”