Liposomal lipid nanoparticles for extrahepatic delivery of mRNA

Long-circulating, transfection-competent lipid nanoparticle (LNP)-mRNA delivery systems are critical for achieving efficient transfection in extrahepatic tissues. Here we investigate the properties of LNP mRNA systems containing high proportions of bilayer forming lipids, using equimolar egg sphingomyelin and cholesterol as the bilayer-forming components. We show that LNP mRNA systems prepared at bilayer lipid to ionizable lipid molar ratios of 4-0.67 exhibit high mRNA encapsulation efficiencies (90-100%) and excellent transfection potencies in vitro. Systems with bilayer lipid to ionizable lipid molar ratios equating to 4 exhibit a liposomal morphology with a solid core suspended in an aqueous interior surrounded by a lipid bilayer. These liposomal LNPs exhibit longer circulation lifetimes than LNP systems with Onpattro-like lipid compositions and have enhanced extrahepatic transfection properties. The prolonged blood circulation lifetime is attributed to reduced plasma protein adsorption. The transfection competency of liposomal LNP systems is attributed to export of the solid core containing mRNA from the LNP as the endosomal pH is lowered.