This may come as a surprise, but your body doesn’t want to turn foreign RNA into foreign proteins. In fact a lot of the cell’s own immune response is dedicated to recognising non-self RNA and destroying it and anything it might make. This is because the sole purpose of viruses is to trick the body into making viral proteins rather than human ones. One of the major barriers is the cell membrane, the lipid bilayer that encapsulates its, keeping all the good stuff in and the bad stuff out. RNA is a big, long and importantly charged molecule. The membrane, because it is hydrophobic, repels these kind of molecules – thereby protecting the contents of the cell. There are also enzymes that target the RNA for destruction, making the whole environment pretty inhospitable for RNA. With RNA vaccines, we are trying to mimic the viral life cycle to train the body to recognise the proteins made so it can better fight off the virus when it encounters them. So one of the major challenges in RNA vaccine development is how best to package the material to get it into cells.
In the first generation of RNA vaccines, that so successfully reduced the burden of disease during the COVID-19 pandemic, this packaging problem was solved with a technology called LNPs (or Lipid Nanoparticles). These are a combination of fatty acids that encapsulated the RNA and allow it to enter the cells. There are, however, some limitations with LNP: they are unstable at room temperature, necessitating the ultra-cold storage that was needed during the pandemic; they are somewhat inflammatory, this has mixed blessings as we need the immune system to recognise the foreign proteins but too much inflammation can lead to unwanted side effects and finally the patent space around LNP is very crowded, which may affect wider rollout of vaccines, particularly in low income countries.
There are many alternatives to LNP. One of the major alternative classes is polycationic polymers. These work because the RNA is negatively charged, and so the polymer (because it has a positive charge) neutralises the molecule. This stabilises the RNA and makes it more palatable for the cell to take up. In our recently published study Manipulating the delivery and immunogenicity of DNA vaccines through the addition of CB[8] to cationic polymers; we explored a modification to the polymer approach. In addition to the polymers, we added another component called CB[8]. This is a barrel shaped molecule that can link the polymers together to form a network. They are called cucurbiturils because they are shaped a bit like pumpkins (from the family cucurbit).
When we compared responses between the formulated nucleic acid vaccine with and without the CB[8], we observed a changed in the amount of inflammation induced by the vaccination. This altered the quality of the immune response. Which may be beneficial for future applications where there is a need to deliver nucleic acid but without the immune system seeing it. We are now further developing this platform thanks to support from Innovate UK, working on a project led by Aqdot.