Improvement of PR8-Derived Recombinant Clade 2.3.4.4c H5N6 Vaccine Strains by Optimization of Internal Genes and H103Y Mutation of Hemagglutinin.

Se-Hee An,Chang-Seon Song,Seung-Min Hong,Jin-Ha Song,Jun-Gu Choi,Hyuk-Joon Kwon,Youn-Jeong Lee,Jun-Beom Kim,Chung-Young Lee,Seung-Eun Son,Kang-Seuk Choi,Jae-Hong Kim,Jei-Hyun Jeong

doi:10.3390/vaccines8040781

Se-Hee An, Chang-Seon Song + Show 11 more

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https://doi.org/10.3390/vaccines8040781

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Abstract

Clade 2.3.4.4c H5N6 avian influenza A viruses (AIVs) may have originally adapted to infect chickens and have caused highly pathogenic avian influenza (HPAI) in poultry and human fatalities. Although A/Puerto Rico/8/1934 (H1N1) (PR8)-derived recombinant clade 2.3.4.4c H5N6 vaccine strains have been effective in embryonated chicken eggs-based vaccine production system, they need to be improved in terms of immunogenicity and potential mammalian pathogenicity. We replaced the PB2 gene alone or the PB2 (polymerase basic protein 2), NP (nucleoprotein), M (matrix protein) and NS (non-structural protein) genes together in the PR8 strain with corresponding genes from AIVs with low pathogenicity to remove mammalian pathogenicity and to match CD8+ T cell epitopes with contemporary HPAI viruses, respectively, without loss of viral fitness. Additionally, we tested the effect of the H103Y mutation of hemagglutinin (HA) on antigen productivity, mammalian pathogenicity and heat/acid stability. The replacement of PB2 genes and the H103Y mutation reduced the mammalian pathogenicity but increased the antigen productivity of the recombinant vaccine strains. The H103Y mutation increased heat stability but unexpectedly decreased acid stability, probably resulting in increased activation pH for HA. Interestingly, vaccination with inactivated recombinant virus with replaced NP, M and NS genes halted challenge virus shedding earlier than the recombinant vaccine without internal genes replacement. In conclusion, we successfully generated recombinant clade 2.3.4.4c H5N6 vaccine strains that were less pathogenic to mammals and more productive and heat stable than conventional PR8-derived recombinant strains by optimization of internal genes and the H103Y mutation of HA.

Highlights

Pathogenic avian influenza A viruses (HPAIVs) are highly contagious pathogens causing serious economic and public health problems [1,2]
The high-growth A/Puerto Rico/8/1934 (H1N1) (PR8) strain is high-yielding in embryonated chicken eggs (ECEs), and PR8-based 6+2 recombinant vaccine strains have been used in countries where highly pathogenic avian influenza (HPAI) became endemic [8,9,10]
The internal genes of PR8 have already acquired multiple mutations related to mammalian pathogenicity, and conventional PR8-derived recombinant vaccine strains against HPAI can potentially acquire mammalian pathogenicity in vitro during reverse genetics procedures [11,12]

Summary

Introduction

Pathogenic avian influenza A viruses (HPAIVs) are highly contagious pathogens causing serious economic and public health problems [1,2]. The high-growth A/Puerto Rico/8/1934 (H1N1) (PR8) strain is high-yielding in embryonated chicken eggs (ECEs), and PR8-based 6+2 recombinant vaccine strains have been used in countries where highly pathogenic avian influenza (HPAI) became endemic [8,9,10]. Studies to find internal genes that are less pathogenic to mammals while maintaining viral replication efficiency have been continued by replacing internal genes of PR8 with single PB2 or NS genes and all internal genes of low pathogenic avian influenza viruses (LPAIVs) [12,13,14]

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