Modulation of lipid nanoparticle-formulated plasmid DNA drives innate immune activation promoting adaptive immunity.

Nucleic acid vaccines have grown in importance over the past several years, with the development of new approaches remaining a focus. We describe a lipid nanoparticle-formulated DNA (DNA-LNP) formulation which induces robust innate and adaptive immunity with similar serological potency to mRNA-LNPs and adjuvanted protein. Using an influenza hemagglutinin (HA)-encoding construct, we show that priming with our HA DNA-LNP demonstrated stimulator of interferon genes (STING)-dependent upregulation and activation of migratory dendritic cell (DC) subpopulations. HA DNA-LNP induced superior antigen-specific CD8⁺ T cell responses relative to mRNA-LNPs or adjuvanted protein, with memory responses persisting beyond one year. In rabbits immunized with HA DNA-LNP, we observed immune responses comparable or superior to mRNA-LNPs at the same dose. In an additional model, a SARS-CoV-2 spike-encoding DNA-LNP elicited protective efficacy comparable to spike mRNA-LNPs. Our study identifies a platform-specific priming mechanism for DNA-LNPs divergent from mRNA-LNPs or adjuvanted protein, suggesting avenues for this approach in prophylactic and therapeutic vaccine development.