Genetic Engineering Strategies to Improve Vaccine Effectiveness and Production

Each year influenza kills 500,000 people and infects millions more, with major economic impacts and increased burden on health services. Seasonal vaccination against influenza is an important health measure. However, the current means of vaccine production in embryonated hen eggs is at its limit when it comes to calls for improved vaccine effectiveness and increased production capacity. Our aim is to innovate human flu vaccine production, using synthetic biology and genome engineering technology to enhance the egg micro-environment. These innovations also address an urgent bottleneck in the generation of egg production birds by allowing immediate screening of embryo sex.

We focused on the vaccine inoculum, which adapts to high levels of an alpha-2,3 receptor in embryonated eggs, reducing inoculum immunogenicity. In humans the equivalent receptors are alpha-2,6, but their presence can be affected by over-expression of transferase enzymes.

We also investigated expressing an essential influenza virus gene in embryonated eggs to provide a key component for assembly of functional virus particles. In a reverse engineered vaccine inoculum this genetic component is omitted and can be substituted with a gene to provoke immune responses to other diseases. Replication is restricted outside of embryonated eggs carrying the key genetic component and protection against influenza is provided in addition to agents of rapidly emerging diseases such as SARS-CoV-2.

Insertion of a transgene for the human transferase SIAT1 into the chicken genome converted receptors to alpha-2,6 in tissue cultures and embryonated eggs, and transgene integration on the Z sex chromosome allowed segregation of transgenes to male embryos only. Analysis of inoculum mismatches from SIAT1 embryonated eggs will direct ongoing vaccine effectiveness testing. Support of engineered replication-deficient vaccine strains in engineered chicken tissues further demonstrates how well-equipped synthetic biology is to deliver improvements to the effectiveness and production capacity of influenza vaccines.