Hydrophobic Tail and Linker Diversification of PEG-Lipids Unlocks Precise Muscle Tropism of mRNA-Lipid Nanoparticles.

Intramuscular mRNA lipid nanoparticles (LNPs) often exhibit undesirable liver accumulation, compromising safety and efficacy. While optimization efforts focus on ionizable and helper lipids, the role of trace PEG-lipids remains underexplored. To address this, we constructed a 45-member PEG-lipid library via Ugi/Passerini reactions, keeping the PEG chain constant at 2 kDa while systematically diversifying the hydrophobic tail and linker structures. High-throughput screening identified Pr-182-BNT (P1B LNP) as a lead candidate. P1B LNPs enable highly efficient and selective mRNA delivery to skeletal muscle while drastically minimizing hepatic off-targeting. This precise tropism originates from enhanced muscle cell uptake and optimized membrane interactions, driven by the lipid's unique branched, asymmetric tail. In Ai9 reporter mice, P1B LNPs drive potent muscle-specific gene editing and reduce off-target recombination. As an RSV mRNA vaccine, they elicit robust antigen-specific IgG titers and expands polyfunctional CD8+IFN-γ+ T cells, indicating a Th1-skewed response. By re-engineering only the trace PEG-lipid, this work overcomes a key targeting limitation of classical LNPs and establishes a translatable platform for safer, more effective mRNA vaccines and therapeutics.