Poly(acrylamido) PEG-Alternative Lipids Rescue mRNA Efficacy during Repeated Dosing and Enhance Immune Cell Delivery

Abstract Following the successes of the messenger RNA (mRNA) lipid nanoparticle (LNP) vaccines against COVID-19, mRNA-LNPs are being explored for varied multidose applications including cancer immunotherapies and protein replacement therapies. LNPs rely on poly(ethylene glycol)-lipid (PEG-lipid) coatings for stability, but increasing anti-PEG antibody prevalence threatens repeat-dose efficacy and increases pseudoallergic risk, creating an urgent need for alternatives. Here, we introduce poly(acrylamido) lipids (PAM-lipids), a family of polymer lipids that effectively replace PEG-lipids in mRNA-LNP formulations. Systematic variation of monomer chemistry, molar mass, and end group reveals critical structure–activity relationships determining LNP size, polydispersity, and transfection efficiency. Varying PAM monomer chemistry allows minimization of antipolymer antibody cross-reactivity, with multiple PAM-lipids demonstrating no anti-PEG antibody binding. Several PAM-LNPs exhibit superior mRNA transfection efficacy to PEGylated clinical benchmarks in vitro and in vivo across multiple cell types, organs, routes of administration, and mRNA cargos. In particular, lead PAM-LNPs enhance mRNA delivery to dendritic cells (up to 120-fold in vitro and 3-fold in vivo) and macrophages (4-fold in vivo), with 2.5-fold superior lymph node expression, driven in part by increased cellular association and lymphoid targeting. Crucially, PAM-LNPs evade circulating anti-PEG antibodies to rescue lost mRNA efficacy after repeated dosing, resulting in 300% mRNA expression relative to that of PEG-LNPs. These findings demonstrate PAM-lipids as a chemically varied, immunologically compatible family of PEG alternatives for mRNA-LNP therapeutics.