The effect of neutralization of a cationic polymeric vaccine delivery system via addition of an anionic polymer on protein expression

Next generation vaccines have arisen as a quick response to the SARS-Cov-2 pandemic. This technology uses genetic material for immunization and allows a cost effective and adaptive method in comparison to classic vaccine platforms. Nevertheless, said genetic sequence needs an appropriate method in order to be delivered to host cells efficiently, promote cellular uptake and prevent degradation. In this study, the delivery of self-amplifying RNA (saRNA) using a cationic polymer is analysed. Nanoparticles were formulated via self assembly, using the polymer poly (cystamine bisacrylamide-co-4-amino-1-butanol) (pABOL) as well as saRNA coding for the gene of interest, firefly luciferase. Surface charge is one of the main differences seen when comparing the encapsulation of these nanoparticles to the FDA approved lipid nanoparticles (LNPs), LNPs are neutral, whereas pABOL nanoparticles are cationic. And although LNP delivery has led to an overall higher immune response, pABOL delivery has induced 100x higher intramuscular protein expression. Therefore, the surface charge of pABOL nanoparticles was modified in order to study characteristics such as size, polydispersity index and protein expression in vitro. The anionic polymer polyglutamic acid (PGA) was used and a series of formulations using different weight to weight ratios of PGA to pABOL were prepared. This polymer has been previously added to cationic lipoparticles so as to modify its surface charge and study the effect on the biodistribution. Increasing levels of PGA led to anionic particles, as expected, and protein expression levels comparable to that of cationic particles formulated without PGA. It was also seen that neutral particles showed particle sizes of approximately 1000 nm and a significantly lower protein expression when tested in vitro. The formulation technique was also studied. We found that for 50 μL doses prepared for in vitro experiments, there were no significant differences in the particle characteristics when formulation methods varied, but this was not the case for in vivo formulations. Overall, PGA showed itself to be a promising polymer to complement pABOL characteristics when used as a delivery system for genetic material and we hypothesize that this has the potential to alter cellular tropism.