Oligomeric Recombinant H5 HA1 Vaccine Produced in Bacteria Protects Ferrets from Homologous and Heterologous Wild-Type H5N1 Influenza Challenge and Controls Viral Loads Better than Subunit H5N1 Vaccine by Eliciting High-Affinity Antibodies

Abstract

Only the oligomeric rHA1 (not the monomeric rHA1) immunogen and the SU-H5N1 vaccine provided protection against the lethality and morbidity of homologous and heterologous highly pathogenic H5N1. Oligomeric rHA1 generated more cross-neutralizing antibodies and higher levels of serum antibody binding to HA1, with stronger avidity and a better IgG/IgM ratio, than monomeric HA1 and SU-H5N1 vaccines, as determined by surface plasmon resonance (SPR). Importantly, viral loads after heterologous H5N1 challenge were more efficiently controlled in ferrets vaccinated with the oligomeric rHA1 immunogen than in SU-H5N1-vaccinated ferrets. The reduction of viral loads in the nasal washes correlated strongly with higher-avidity antibodies to oligomeric rHA1 derived from H5N1 clade 1 and clade 2.2 viruses, as measured by SPR. This is the first study to show the role of antibody avidity for the HA1 globular head domain in reduction of viral loads in the upper respiratory tract, which could significantly reduce viral transmission.

H5 N-terminal β sheet promotes oligomerization of H7-HA1 that induces better antibody affinity maturation and enhanced protection against H7N7 and H7N9 viruses compared to inactivated influenza vaccine

“…These earlier HA-structural studies did not describe the oligomerization signal in the HA1 globular domain identified in the current study, suggesting that in the presence of HA2 the N-terminus ␤-sheet structure is engaged in HA1-HA2 bridge and not in HA1 oligomerization. However, in the absence of HA2 sequence, the HA1 globular head formed oligomers and agglutinate human RBC, as was observed with multiple group-1 influenza subtype strains produced by our group [1][2][3][4]. It is likely that in the native spikes the N-terminal ␤-sheets of the three HA1 globular domains are not in sufficient proximity to form oligomers, but in the absence of HA2 they are free and close enough to provide the needed oligomerization signal.…”

“…To that end, we measured the antibody affinity (antigen-antibody complex dissociation rates) of post-first and post-second vaccination ferret sera from all vaccinated ferrets as previously described [4,11]. As can be seen in Fig.…”

“…Steady-state equilibrium binding of post-H7 vaccination animal sera was monitored at 25 • C using a ProteOn surface plasmon resonance biosensor (BioRad Labs) as previously described for H5N1 and pH1N1 post-vaccination sera [4,11,12]. The H7 rHA1 protein was coupled to a GLC sensor chip (BioRad Labs) with amine coupling with 500 resonance units (RU) in the test flow cells.…”

“…Recently, we demonstrated that bacterially produced influenza HA1 globular domain from several pandemic strains from Group 1 (including H1N1pdm09 and two H5N1 viruses) are properly folded and form functional oligomers that can agglutinate red blood cells (RBC). The oligomerization signal was mapped to the N-terminal ␤-sheet of HA1 [1][2][3][4]. Importantly, the recombinant oligomeric HA1 proteins elicited high titers of neutralizing antibodies in both rabbits and sheep that demonstrated strong protection of animals against both homologous and heterologous H5N1 avian strains in a ferret challenge model [2][3][4].…”

A recombinant protein containing highly conserved hemagglutinin residues 81-122 of influenza H5N1 induces strong humoral and mucosal immune responses

“…Recombinant subunit vaccines incorporating antigenic viral membrane glycoproteins, especially hemagglutinin (HA), are attractive vaccine candidates since they are able to induce virus-neutralizing antibodies (5-7). The HA subunit 1 (HA1) has been previously shown as an important antigen to induce neutralizing antibodies and protect against IAV challenge (5,8). The amino acids of HA1 tend to develop continuous mutation, but some conserved regions with limited changes are still found throughout the passage.…”