Induction of Bleb Structures in Lipid Nanoparticle Formulations of mRNA Leads to Improved Transfection Potency

The transfection potency of lipid nanoparticle (LNP) mRNA systems is critically dependent on the ionizable cationic lipid component. LNP mRNA systems composed of optimized ionizable lipids often display distinctive mRNA-rich "bleb" structures. Here, it is shown that such structures can also be induced for LNPs containing nominally less active ionizable lipids by formulating them in the presence of high concentrations of pH 4 buffers such as sodium citrate, leading to improved transfection potencies both in vitro and in vivo. Induction of bleb structure and improved potency is dependent on the type of pH 4 buffer employed, with LNP mRNA systems prepared using 300 mm sodium citrate buffer displaying maximum transfection. The improved transfection potencies of LNP mRNA systems displaying bleb structure can be attributed, at least in part, to enhanced integrity of the encapsulated mRNA. It is concluded that enhanced transfection can be achieved by optimizing formulation parameters to improve mRNA stability and that optimization of ionizable lipids to achieve enhanced potency may well lead to improvements in mRNA integrity through formation of the bleb structure rather than enhanced intracellular delivery.