S. Berryman - The use of reverse genetics to facilitate the growth of FMDV for the production [...]

S. Berryman - The use of reverse genetics to facilitate the growth of FMDV for the production of vaccines

Session: Improving conventional vaccines

Open Session of the EuFMD – 2018 – Increasing Global Security in the supply of effective vaccines – 29-31 October 2018 -Borgo Egnazia, Italy

Introduction
FMD vaccines are chemically-inactivated virus preparations produced in BHK-21 mammalian cell culture. Since FMDV exists as a number of constantly evolving serotypes, there is a periodic need to produce new vaccines against emerging strains. However, field viruses typically show poor growth in cell culture, and require serial passage to adapt. Adaptation to cell culture often involves selection of variants with altered receptor specificity that are no longer dependent upon integrin receptors for infection.

Materials and Methods
We have used reverse genetics to produce recombinant FMDVs from the four most prevalent FMDV serotypes (Type O, A, Asia-1 and SAT2), carrying defined mutations in the capsid designed to improve growth in cell culture without the need for cell culture adaptation. The capsid encoding sequence, containing targeted mutations to confer cell culture adaptation, was introduced in to an existing reverse genetics system. Recombinant viruses were rescued by transfection of plasmid derived RNA into cell cultures, and deep sequenced. Growth of viruses carrying wild type and mutated capsids was compared, both in adherent and suspension BHK cells.

Results
In all four serotypes we were able to identify virus variants with targeted capsid mutations which showed improved growth relative to wild type, either in terms of increased speed of growth, improved titre/yield, or both. We have also used antisera in virus neutralisation assays to compare the antigenicity of the viruses.

Discussion
In summary, we have used a reverse genetics approach to introduce targeted capsid changes to FMDV field viruses to improve growth in cell culture, without the need for adaptation by cell culture passage. This approach could greatly speed up the production of FMDV vaccine viruses from new field strains, by reducing the need for cell culture adaptation by passage and reducing the testing required for extraneous agents, since virus is produced recombinantly.

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