Nitric oxide-assisted lipid nanoparticles amplify mRNA vaccine responses.

mRNA vaccines have made substantial clinical advances, yet their full clinical potential can be further expanded by enhancing cytosolic delivery. Here, we integrate a nitric oxide (NO) generator with lipid nanoparticles (LNPs) to boost mRNA delivery efficiency and mRNA-based vaccine efficacy. SM-102/DEA LNPs, the lead formulation, achieved significantly higher mRNA delivery compared with the FDA approved SM-102 LNPs in both cellular and animal models. The intramuscular administration of SM-102/DEA LNPs encapsulating mRNA encoding SARS-CoV-2 spike protein elicited substantially higher anti-spike IgG levels and robust CD8+ and CD4+ T cell responses compared to SM-102 LNPs. Mechanistic studies revealed that DEA incorporation promotes endosomal escape of mRNA cargos in SM-102/DEA LNPs. These findings establish NO-assisted LNPs as a unique platform for potent mRNA delivery, which provides a new paradigm for overcoming endosomal barriers and improving the efficacy of mRNA vaccines.