Safety, immunogenicity and protection of A(H3N2) live attenuated influenza vaccines containing wild-type nucleoprotein in a ferret model

Abstract

Live attenuated influenza vaccines (LAIVs) are promising tools for the induction of broad protection from influenza due to their ability to stimulate cross-reactive T cells against influenza pathogens. One of the major targets for cytotoxic T-cell immunity is viral nucleoprotein (NP), which is relatively conserved among antigenically distant influenza viruses. Nevertheless, a diversity of epitope composition has been found in the NP protein of different lineages of influenza A viruses. The H2N2 master donor virus which is currently used as a backbone for the LAIV and donor of the six genomic segments encoding the internal proteins, A/Leningrad/134/17/57 (MDV Len/17), was isolated 60 years ago. As such, NP-specific T-cell immunity induced upon vaccination with classical LAIVs with a 6:2 genome composition containing this older NP might be suboptimal against currently circulating influenza viruses. In this study, a panel of H3N2 LAIV candidates with wild-type NP genes derived from circulating viruses were generated by reverse genetics (5:3 genome composition). These viruses displayed the cold adaptation and temperature sensitivity phenotypes of MDV Len/17 in vitro. LAIVs with both 6:2 and 5:3 genome compositions were attenuated and replicated to a similar extent in the upper respiratory tract of ferrets. LAIVs were immunogenic as high neutralizing and hemagglutination inhibition serum antibody titers were detected 21 days after infection. All vaccinated animals were protected against infection with heterologous H3N2 influenza A viruses. Thus, LAIV with a 5:3 genome composition is safe, immunogenic and can induce cross-protective immunity.

A Live Attenuated Influenza Vaccine Elicits Enhanced Heterologous Protection When the Internal Genes of the Vaccine Are Matched to Those of the Challenge Virus

“…T-cell-mediated immunity is critical for protective immune responses against natural IAV infection (9-16), but current influenza vaccines elicit poor CD8 ϩ T-cell responses (44). Despite this, few studies have attempted to enhance T-cell immunity in an IAV vaccine, and those that have have focused principally on a single protein component of IAV (45)(46)(47)(48). Much greater efforts have been directed toward the generation of broadly reactive (and broadly neutralizing) antibody responses (49,50).…”

Sequential Immunization with Universal Live Attenuated Influenza Vaccine Candidates Protects Ferrets against a High-Dose Heterologous Virus Challenge

“…Our previous comparative ferret study of H3N2 LAIVs containing NP from MDV or wild-type virus did not detect significant differences in the cross-protective efficacy of the vaccines, although there was a slightly lower challenge virus titer in the URT in the WT NP LAIV group. This was probably because the challenge virus failed to replicate in lungs and did not cause significant pathology [58]. In contrast to that study, here we used a high-dose viral challenge that induced significant pathology and clinical manifestations of disease in the control animals, allowing the protective potential of the vaccines to be evaluated through a number of parameters.…”

Sequential Immunization with Universal Live Attenuated Influenza Vaccine Candidates Protects Ferrets against a High-Dose Heterologous Virus Challenge

“…Our previous comparative ferret study of H3N2 LAIVs containing NP from MDV or wildtype virus did not detect significant differences in the cross-protective efficacy of the vaccines, although there was a slightly lower challenge virus titer in the URT in WT NP LAIV group. This was probably because the challenge virus failed to replicate in lungs and did not cause significant pathology [54]. In contrast to that study, here we used a high-dose viral challenge that induced significant pathology and clinical manifestations of disease in the control animals, allowing the protective potential of the vaccines to be evaluated through a number of parameters.…”