Treatment targets, vaccine targets and delivery models

You will be aware that there has been a worldwide race to develop vaccines against COVID-19.

There have been several different approaches taken but most use the coronavirus surface spike protein as a target to raise antibodies against. This is partly because the spike protein is stable and conserved in the different evolving strains but also because it is how the coronavirus attaches to and enters human cells so blocking that was thought to be likely to provide an effective immunisation strategy.

Our first available vaccine from Pfizer is an mRNA encoding the spike protein which is delivered into our cells encased in a lipid biosphere. Once inside the cell, the host synthetic machinery reads the mRNA code to make coronavirus spike protein which then appears as a foreign entity which raises an antibody response. The first jab primes our immune systems and the second jab re-enforces and produces a sustained antibody response. The Moderna vaccine works similarly but the delivery mechanism is slightly different so that the storage and use requirements are less stringent. This use of mRNA encoding a pathogenic target to create an immune response has not previously been attempted as previously vaccines have been developed either using inactivated whole pathogen or a part of the pathogen.

The team from the Jenner Institute in Oxford, the Oxford Vaccine group led by Professor Sarah Gilbert, also started working on a vaccine as soon as the COVID-19 genome was published. They are teamed with AstraZeneca and their vaccine utilises a primate adenovirus vector to carry the spike protein gene into cells where again the spike protein is produced and an immune response raised. Again, two doses will be needed but this technology is more tried and tested and can be stored and transported at normal fridge temperature making global roll out much easier.