Lipid nanoparticle (LNP) formulations of mRNA vaccines have played a pivotal role in combatting SARS-CoV-2 infections and are expected to be a useful vaccine modality against other pathogens. However, the instability of mRNA-LNP vaccines requires their storage at temperatures below 0 °C and presents manufacturing challenges. We describe thermally stable, lipid-free mRNA vaccines prepared by spray-drying to embed mRNA within glassy polysaccharide microparticles, followed by atomic layer deposition (ALD) to encapsulate the microparticles within protective alumina shells that provide temporally controlled antigen release and facilitate cellular uptake. Using mRNAs encoding for ovalbumin, the modified HIV envelope trimer protein N332-GT2, and green fluorescent protein (GFP), we show that alumina-coated microparticles containing lipid-free mRNA are internalized by cultured macrophages in vitro, elicit robust immune responses compared to LNP-based mRNA vaccines in vivo, and are stable when stored for 6 months at temperatures up to 40 °C. Thus, alumina-coated mRNA vaccines may overcome current limitations of mRNA-LNP vaccines without using LNPs or other lipid-based carriers.
