Sequential Immunization With Live-Attenuated Chimeric Hemagglutinin-Based Vaccines Confers Heterosubtypic Immunity Against Influenza A Viruses in a Preclinical Ferret Model

Abstract

Due to continuous antigenic drift and occasional antigenic shift, influenza viruses escape from human adaptive immunity resulting in significant morbidity and mortality in humans. Therefore, to avoid the need for annual reformulation and readministration of seasonal influenza virus vaccines, we are developing a novel chimeric hemagglutinin (cHA)-based universal influenza virus vaccine, which is comprised of sequential immunization with antigens containing a conserved stalk domain derived from a circulating pandemic H1N1 strain in combination with “exotic” head domains. Here, we show that this prime-boost sequential immunization strategy redirects antibody responses toward the conserved stalk region. We compared the vaccine efficacy elicited by distinct vaccination approaches in the preclinical ferret model of influenza. All ferrets immunized with cHA-based vaccines developed stalk-specific and broadly cross-reactive antibody responses. Two consecutive vaccinations with live-attenuated influenza viruses (LAIV-LAIV) conferred superior protection against pH1N1 and H6N1 challenge infection. Sequential immunization with LAIV followed by inactivated influenza vaccine (LAIV-IIV regimen) also induced robust antibody responses. Importantly, the LAIV-LAIV immunization regimen also induced HA stalk-specific CD4 + IFN-γ + and CD8 + IFN-γ + effector T cell responses in peripheral blood that were recalled by pH1N1 viral challenge. The findings from this preclinical study suggest that an LAIV-LAIV vaccination regimen would be more efficient in providing broadly protective immunity against influenza virus infection as compared to other approaches tested here.

Historical H1N1 Influenza Virus Imprinting Increases Vaccine Protection by Influencing the Activity and Sustained Production of Antibodies Elicited at Vaccination in Ferrets

“…Furthermore, the antibodies elicited had greater neutralization activity suggesting that the mechanism of milder disease at challenge was the ability to develop more functional virus inhibiting antibodies. Similar trends showing increased inactivated influenza virus vaccine responses in primed Live Attenuated Influenza Vaccine (LAIV) vaccinated ferrets have been reported suggesting that a conserved priming effect may occur after a live virus exposure [42][43][44][45]. Using ferret and African Green Monkey models as well as human subjects, these studies showed that priming effects were seen after LAIV administration in the respiratory route but not from priming with inactivated virus vaccination through the intramuscular route [44] indicating the importance of site-specific respiratory tract priming prior to inactivated vaccination.…”

Adeno‐associated virus‐vectored influenza vaccine elicits neutralizing and Fcγ receptor‐activating antibodies

“…The observed lack of protection in QIV‐immunized ferrets is counterintuitive. However, this finding recapitulated observations by others and likely depended on a failure to induce HAI + antibodies by the commercial, non‐adjuvanted human vaccine (Baras et al , ; Nachbagauer et al , ; Liu et al , ). Neither in ferrets nor mice, change of the AAV vector capsid was required to achieve high influenza‐specific antibody titers upon intranasal vaccination, even in the presence of AAV9‐neutralizing serum antibodies.…”

Broadly Protective Strategies Against Influenza Viruses: Universal Vaccines and Therapeutics

“…Another method of improving exposure of the HA stalk domain involves the generation of chimeric HAs (cHA) that express the head domain from one virus strain and the stalk domain of another. This method involves sequential immunization with constructs that express the same stalk domain but different "exotic" head domains, thereby specifically stimulating stalk-directed antibody responses to induce broader protection than strainspecific HA head directed antibodies generated by seasonal vaccines Pica et al, 2012;Krammer et al, 2013;Margine et al, 2013;Nachbagauer et al, 2017;Liu et al, 2019). Sequential vaccination of mice with cHA containing the same H1 stem but different heads demonstrated protection against challenge from Group 1 viruses but not Group 2 viruses .…”