An Adenovirus-Vectored Influenza Vaccine Induces Durable Cross-Protective Hemagglutinin Stalk Antibody Responses in Mice

Abstract

Currently licensed vaccines against the influenza A virus (IAV) need to be updated annually to match the constantly evolving antigenicity of the influenza virus glycoproteins, hemagglutinin (HA), and neuramidiase (NA). Attempts to develop universal vaccines that provide broad protection have resulted in some success. Herein, we have shown that a replication-deficient adenovirus expressing H5/M2e induced significant humoral immunity against the conserved HA stalk. Compared to the humoral responses induced by an inactivated influenza vaccine, the humoral responses induced by the adenovirus-vectored vaccine against the conserved stalk domain mediated cross-protection against heterosubtypic influenza viruses. Importantly, virus inactivation by formaldehyde significantly reduced the binding of monoclonal antibodies (mAbs) to the conserved nucleoprotein (NP), M2e, and HA stalk. These results suggest that inactivation by formaldehyde significantly alters the antigenicity of the HA stalk, and suggest that the conformation of the intact HA stalk provided by vector-based vaccines is important for induction of HA stalk-binding Abs. Our study provides insight into the mechanism by which a vector-based vaccine induces broad protection by stimulation of cross-protective Abs targeting conserved domains of viral proteins. The findings support further strategies to develop a vectored vaccine as a universal influenza vaccine for the control of influenza epidemics and unpredicted pandemics.

Inactivation methods for whole influenza vaccine production

“…Furuya et al also showed that interferon (IFN) type‐1 production, induced by formalin inactivated H1N1 and H3N2 WIV vaccine, is mainly based on TLR7‐MyD88 pathway . Regarding the significant role of keeping the structural integrity of protective epitopes during inactivation to develop cross‐protective immune responses, these data may help explain the lower level of induction of cross‐protection by formalin‐treated viruses …”

“…So that, depending on the type of vaccine, this chemical agent should be removed, diluted, and/or converted into a nontoxic form after treatment, which is a time‐consuming process 32 . On the other hand, viral antigenic epitope alteration based on chemical modifications induced by formaldehyde may lead to undesirable impacts on the antigenicity and efficacy of vaccines 33,34 . For instance, it has been shown that free formaldehyde present in inactivated whole H1N1 vaccine can reduce the induction of monoclonal antibodies (mAbs) against conserved epitopes of influenza virus 33 .…”

“…On the other hand, viral antigenic epitope alteration based on chemical modifications induced by formaldehyde may lead to undesirable impacts on the antigenicity and efficacy of vaccines 33,34 . For instance, it has been shown that free formaldehyde present in inactivated whole H1N1 vaccine can reduce the induction of monoclonal antibodies (mAbs) against conserved epitopes of influenza virus 33 . Alternatively, based on the study of Budimir et al, damage to viral membrane fusion protein in formaldehyde‐inactivated H5N1 WIV vaccine can reduce viral endosomal escape potency 11 .…”

Novel Platforms for the Development of a Universal Influenza Vaccine

“…An adenovirus vector expressing NP and M2 proteins conferred protection from highly virulent H5N1, H1N1, and H3N2 influenza viruses ( 178 ) as well as reduced viral transmission from vaccinated and infected mice to unvaccinated mice ( 178 , 179 ). Furthermore, Kim et al employed a novel approach to inducing cross-reactive immune responses against HA protein by generating recombinant human adenovirus 5 vector encoding full length HA (from H5N1) and four tendem copies of M2e domain (rAdH5/M2e) ( 180 ). Adenovirus vaccine induced antibody-mediated cross-protection against heterosubtypic viruses in mice ( 180 ).…”

“…Furthermore, Kim et al employed a novel approach to inducing cross-reactive immune responses against HA protein by generating recombinant human adenovirus 5 vector encoding full length HA (from H5N1) and four tendem copies of M2e domain (rAdH5/M2e) ( 180 ). Adenovirus vaccine induced antibody-mediated cross-protection against heterosubtypic viruses in mice ( 180 ).…”