Poly(acrylamido) PEG-alternatives Enhance mRNA-LNP Efficacy in Immune Cells and Evade anti-PEG Antibodies During Repeated Dosing

Fiedler, B. M.; Galley, C.; Strimaite, M.; Cheng, N. M.; Mahmoudi, N.; Feng, Z.; Kalber, T. M.; Martinez-Bravo, M.-J.; Morris, C.; Lam, J. K. W.; Stuckey, D. J.; Williams, G. R.; Bennett, C. L.; Gurnani, P.

doi:10.64898/2026.02.26.708093

bioRxiv · 10.64898/2026.02.26.708093

Poly(acrylamido) PEG-alternatives Enhance mRNA-LNP Efficacy in Immune Cells and Evade anti-PEG Antibodies During Repeated Dosing

Fiedler, B. M.·Galley, C.·Strimaite, M.·Cheng, N. M.·Mahmoudi, N.·Feng, Z.·Kalber, T. M.·Martinez-Bravo, M.-J.·Morris, C.·Lam, J. K. W.·Stuckey, D. J.·Williams, G. R.·Bennett, C. L.·Gurnani, P.

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Abstract

Following the successes of the messenger RNA (mRNA) lipid nanoparticle (LNP) vaccines during the COVID-19 pandemic, mRNA-LNPs are being explored for many critical disease indications including infectious disease vaccination, cancer immunotherapies, and protein replacement therapies. LNPs require a polymer coating to provide stability in storage, and to minimise clearance from the body by reducing protein adsorption after injection. Poly(ethylene glycol)-lipids (PEG-lipids) have fulfilled this role to date, however increasing prevalence of antibodies against PEG in the general population jeopardises the efficacy of future PEGylated LNP doses and increases the likelihood of adverse pseudo-allergic responses. There is, therefore, an urgent unmet need to develop LNPs with new surfaces of PEG-alternative polymers which can evade anti-PEG antibodies, particularly where repeat dosing is required. Here, we present a family of polymer lipids, poly(acrylamido) (PAM) lipids, which effectively replace conventional PEG-lipids in mRNA-LNP formulations. We identify key design parameters to show that PAM-lipid monomer chemistry, molar mass and end-group all have critical effects on LNP size, polydispersity and in vitro transfection efficiencies, while having little impact on LNP morphology or internal structure. We determine that side-group (monomer) chemistry is a key mediator in alleviating anti-polymer antibody cross-reactivity. Compared to clinical benchmark PEGylated LNPs, several PAM-LNPs displayed improved transfection efficacy across multiple mRNA cargos in diverse cell types, organs, and routes of administration, both in vitro and in vivo. In particular, mRNA transfection improved in immune cells both in vitro (up-to 120-fold), and in vivo (up-to 5-fold), including superior mRNA expression in lymph nodes (2.5-fold). In part, this is likely because PAMs increase LNP uptake/association with primary immune cells (BMDCs), and increase biodistribution to the lymphoid tissues (LNs, spleen). Crucially, PAM-LNPs avoid circulating anti-PEG antibodies to recover lost mRNA efficacy after repeated dosing in vivo, 300% higher than PEG-LNPs. Overall, our findings establish the PAM-lipid family as a versatile platform of chemically varied PEG-alternatives, towards the next generation of therapeutic mRNA-LNP technologies. Graphical Abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=103 SRC="FIGDIR/small/708093v1_ufig1.gif" ALT="Figure 1"> View larger version (31K): org.highwire.dtl.DTLVardef@107de1aorg.highwire.dtl.DTLVardef@186b6eforg.highwire.dtl.DTLVardef@1542371org.highwire.dtl.DTLVardef@e2d47f_HPS_FORMAT_FIGEXP M_FIG C_FIG

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Fiedler, B. M., Galley, C., Strimaite, M., Cheng, N. M., Mahmoudi, N., Feng, Z., Kalber, T. M., Martinez-Bravo, M.-J., Morris, C., Lam, J. K. W., Stuckey, D. J., Williams, G. R., Bennett, C. L., Gurnani, P.. 2026-02-28. Poly(acrylamido) PEG-alternatives Enhance mRNA-LNP Efficacy in Immune Cells and Evade anti-PEG Antibodies During Repeated Dosing. https://doi.org/10.64898/2026.02.26.708093

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