The Ability of a Non-Egg Adapted (Cell-Like) A(H1N1)pdm09 Virus to Egg-Adapt at HA Loci Other than 222 and 223 and Its Effect on the Yield of Viral Protein.

Carolyn Nicolson,Othmar G Engelhardt,Ruth Harvey,James S Robertson,Victor C Huber

doi:10.1371/journal.pone.0166761

Carolyn Nicolson, Othmar G Engelhardt + Show 3 more

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https://doi.org/10.1371/journal.pone.0166761

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Abstract

Previous studies on influenza A(H1N1)pdm09 candidate vaccine viruses (CVVs) that had adapted to growth in embryonated chicken eggs by the acquisition of amino acid substitutions at HA positions 222 or 223 showed that improved protein yield could be conferred by additional amino acid substitutions in the haemagglutinin (HA) that arose naturally during passaging of the virus in eggs. In this study we investigated, by means of reverse genetics, the ability of a non-egg adapted (cell-like) A(H1N1)pdm09 virus to egg-adapt at HA loci other than 222/223, introducing amino acid substitutions previously identified as egg adaptations in pre-H1N1pdm09 H1N1 viruses and assessing their effect on protein yield and antigenicity. We also investigated the effect on the protein yield of these substitutions in viruses that had A(H1N1)pdm09 internal genes rather than the traditional PR8 internal genes of a CVV. The data show that a cell-like A/Christchurch/16/2010 can be egg-adapted via amino acid substitutions in at least three alternative HA loci (187, 190 and 216), in viruses with either PR8 or A/California/7/2009 internal genes, but that the effects on protein yield vary depending on the amino acid substitution and the internal genes of the virus. Since CVVs need to produce high protein yields to be suitable for vaccine manufacture, the findings of this study will assist in the future characterisation of both wild type viruses and lab-derived CVVs for vaccine use.

Highlights

Influenza is an annual global threat to public health, mitigated by seasonal vaccination
It is expected that H1N1 virus will undergo antigenic drift and new egg isolates will be required for inclusion in future seasonal vaccines
Known substitutions that occurred during egg-adaptation of A(H1N1)pdm09 viruses [1], and those that occurred during egg-adaptation of pre-H1N1pdm09 H1N1 viruses [3,4] at these equivalent loci, were introduced into a non-egg adapted A/Christchurch/16/2010 HA gene using reverse genetics

Summary

Introduction

Influenza is an annual global threat to public health, mitigated by seasonal vaccination. Each new candidate vaccine virus (CVV) needs to be adapted to growth in embryonated hens’ eggs, whilst maintaining the appropriate antigenicity. Egg-Adaptation of Cell-Like A(H1N1)pdm Influenza Viruses and Effect on Yield have amino acid substitutions around the receptor binding site of the haemagglutinin (HA) that can impact on viral attributes such as antigenicity and growth [1, 2]. Known substitutions that occurred during egg-adaptation of A(H1N1)pdm viruses [1], and those that occurred during egg-adaptation of pre-H1N1pdm H1N1 viruses [3,4] at these equivalent loci, were introduced into a non-egg adapted (cell-like) A/Christchurch/16/2010 HA gene using reverse genetics

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