The development of mRNA-based antiviral and antitumor therapeutics is progressing rapidly and shows considerable promise. Optimizing the composition of liposomal delivery vehicles is critical for enhancing mRNA vaccine efficacy. Among their components, PEG-lipids require careful optimization to improve the colloidal stability of mRNA-liposome complexes, prolong their in vivo circulation time, and enhance mRNA delivery efficiency, thereby eliciting a robust immune response. Here, we report a structure-functional analysis of PEG-lipids incorporated into cationic liposomes based on the cationic lipid 2X3 and the helper lipid DOPE. The following parameters of PEG-lipids were varied: PEG chain length (800-2000 Da), PEG-lipid architecture (classical head-to-tail vs. gemini-like structures), hydrophobic anchor chain length (C14 octadecyl and C18 tetradecyl residues) and molar amount of PEG-lipid in formulations (0.5-4 mol%). We demonstrated that optimized liposomes contained 4 mol% of a PEG-lipid composed of linear PEG2000 conjugated to a C14-dialkylglycerol anchor via a carbamate linker. This formulation enabled efficient in vivo expression of luciferase-encoding mRNA and, upon delivery of influenza A/California//07/09 (H1N1pdm09) hemagglutinin-encoding mRNA, induced robust antigen-specific humoral and cellular immunity. Our findings underscore the critical importance of PEG-lipid optimization for advancing potent mRNA delivery platforms for antiviral and antitumor vaccines.
