Plasmid DNA vaccines encapsulated in lipid nanoparticles elicit STING-dependent type 1 interferon release

Plasmid DNA vaccines have excellent safety, stability, and tolerability profiles, making them a popular choice for cancer immunotherapy. However, challenges in targeted delivery to professional antigen-presenting cells, and the requirement for nuclear translocation of DNA, have limited the immunogenicity of this approach. The implementation of ionizable lipid nanoparticles (LNPs) for mRNA vaccines has enabled robust cellular and humoral immunity profiles after immunization. Here, we sought to determine whether encapsulation of plasmid DNA in ionizable LNP could improve DNA vaccine efficacy. Using in vitro and in vivo murine models, we assessed immune profiles, toxicity profiles, and anti-tumor immunity resulting from DNA encapsulated in ionizable LNP used for contemporary mRNA vaccines. LNP encapsulation of plasmid DNA led to differences in resulting immune cell populations, but high doses of DNA encapsulated in LNP led to type I interferon-mediated toxicity. This was mediated by STING activation. However, low doses of plasmid DNA encapsulated in LNP co-delivered with non-encapsulated DNA as a cancer vaccine resulted in reduced tumor growth in tumor-bearing mice. Our data demonstrate that plasmid DNA can be effectively encapsulated by LNP, but careful consideration of dose may be required for this to be applied to cancer vaccine therapies.