Differential Recognition of Computationally Optimized H3 Hemagglutinin Influenza Vaccine Candidates by Human Antibodies

Among circulating influenza viruses in humans, H3N2 viruses typically evolve faster than other subtypes and have caused disease in millions of people since emerging in 1968. Computationally optimized broadly reactive antigen (COBRA) technology is one strategy to broaden vaccine-elicited antibody responses among influenza subtypes. In this study, we determined the structural integrity of an H3N2 COBRA hemagglutinin (HA), TJ5, and we probed the antigenic profile of several H3N2 COBRA HAs by assessing recognition of these immunogens by human B cells from seasonally vaccinated human subjects. Of three recently described COBRA H3 HA antigens (TJ5, NG2, and J4), we determined that TJ5 and J4 HA proteins recognize pre-existing B cells more effectively than NG2 HA and a wild-type Hong Kong/4801/2014 protein. We also isolated a panel of 12 H3 HA-specific human monoclonal antibodies (MAbs) and identified that most MAbs recognize both wild-type and COBRA HA proteins and have functional activity against a broad panel of H3N2 viruses. Most MAbs target the receptor-binding site, and one MAb targets the HA stem. MAb TJ5-5 recognizes TJ5 and J4 COBRA HA proteins but has poor recognition of NG2 HA, similar to the global B-cell analysis. We determined a 3.4 Å structure via cryo-electron microscopy of Fab TJ5-5 complexed with the H3 COBRA TJ5, which revealed residues important to the differential binding. Overall, these studies determined that COBRA H3 HA proteins have correct antigenic and structural features, and the proteins are recognized by B cells and MAbs isolated from seasonally vaccinated humans. IMPORTANCE Vaccine development for circulating influenza viruses, particularly for the H3N2 subtype, remains challenging due to consistent antigenic drift. Computationally optimized broadly reactive antigen (COBRA) technology has proven effective for broadening influenza hemagglutinin (HA)-elicited antibody responses compared to wild-type immunogens. Here, we determined the structural features and antigenic profiles of H3 COBRA HA proteins. Two H3 COBRA HA proteins, TJ5 and J4, are better recognized by pre-existing B cells and monoclonal antibodies from the 2017 to 2018 vaccine season compared to COBRA NG2 and a wild-type A/Hong Kong/2014 HA protein. We determined a cryo-electron microscopy (cryo-EM) structure of one MAb that poorly recognizes NG2, MAb TJ5-5, in complex with the TJ5 COBRA HA protein and identified residues critical to MAb recognition. As NG2 is more effective than TJ5 for the recent Hong Kong/2019 virus, these data provide insights into the diminished effectiveness of influenza vaccines across vaccine seasons.

A potently neutralizing site III-specific human antibody prevents human metapneumovirus replication in vivo

Human metapneumovirus (hMPV) is a leading cause of lower respiratory tract infection in infants and children, yet there is currently no vaccine available for prevention of hMPV disease. hMPV has three surface proteins: the small hydrophobic, the attachment, and the fusion (F) protein. The hMPV F protein is the sole target of neutralizing antibodies. To develop new therapeutics for disease intervention and to inform the development of an effective vaccine, we isolated several new human monoclonal antibodies (mAbs) to the hMPV F protein. A subset of these mAbs were determined to be neutralizing by a plaque reduction assay. The neutralizing mAbs bind to all four subgroups of the hMPV F protein, and neutralize viruses from both the A and B genotypes. We conducted epitope binning assays on the OctetRED384 system to determine the antigenic targets of each mAb. Three of the four mAbs (196, 314, 201) bind near the previously discovered mAb DS7. One mAb, MPV364, competes with the site III mAbs MPE8 and 25P13, yet unlike these mAbs, MPV364 does not cross-react with the respiratory syncytial virus F protein. MPV364 exhibits potent and broadly neutralizing activity below 20 ng/mL. We examined the therapeutic efficacy of MPV364 to prevent replication of hMPV in vivo and found a reduction in lung viral titers. These data suggest antigenic site III on the hMPV F protein elicits potently neutralizing mAbs, and should be incorporated into future vaccine candidates. Furthermore, MPV364 should be further examined for protection from hMPV disease in additional animal models of infection.