Ultra-compacted single self-amplifying RNA molecules as quintessential vaccines

Abstract

We introduce aqueous phases comprising single, highly compacted self-amplifying messenger RNA (saRNA) molecules, that are suitable for prophylactic and therapeutic application, specifically for vaccination against infectious diseases. The formulations are formed in the presence of the positively charged polymer polyethylenimine (PEI), which leads to condensation of the single saRNA molecules into a globular organization with high packing density, low mass fraction of polymer, and, consequently, very small size. In this format, they display improved biological activity in comparison to previously described saRNA/PEI nanoparticlulate formulations, both in vitro and in vivo. Application of the ultra-compacted single saRNA formulation for vaccination, via intramuscular route, results in relevant titers for practical use at lower doses compared to the nanoparticle formulations. These novel saRNA vaccine products can be obtained by straight-forward manufacturing routes, and they can be readily frozen or lyophilized. With these characteristics they can be particularly of interest for future vaccine products even for application under challenging conditions, where requirements such as high activity, good thermostability, low cost of goods, and facilitated logistics need to be fulfilled at the same time. One-Sentence Summary: single saRNA molecules, condensed into an unusually compact globular organization with very small size by an oppositely charged polyelectrolyte (polyethylenimine), are applicable as vaccines, which induce very strong immunological responses at very low doses.