Injection site-retained lipid nanoparticles for targeted intramuscular delivery of mRNA RSV prefusion-F vaccine.

mRNA therapeutics, particularly mRNA vaccines, hold significant promise for a wide range of medical applications. Lipid nanoparticles (LNPs) are the most clinically advanced delivery vehicles for mRNA, but issues such as off-target effects and liver accumulation hinder their broader clinical adoption. In this study, we designed and synthesized a library of 26 novel ionizable lipids to screen for better delivery efficiency and tissue specificity. After formulating into LNPs, these ionizable lipids exhibited favorable physicochemical properties. In vitro transfection and cytotoxicity assays revealed that LNPs formulated with YK-201, YK-202, and YK-209 showed superior transfection efficiency and low cytotoxicity. In a mouse model, intramuscular injection of Fluc mRNA-LNPs resulted in sustained and localized protein expression at the injection site. When applied to prepare RSV preF-mRNA vaccines, these novel LNPs elicited robust humoral immune responses and reduced lung damage, outperforming the clinically used SM-102. The safety of the LNP formulations was subsequently demonstrated in a mouse model. Collectively, these findings highlight the potential of these novel ionizable lipids as effective injection site-retained mRNA vaccine delivery vehicles.