Abstract
mRNA vaccines were successfully developed and approved for emergency use to fight coronavirus disease 2019. However, the effect of DNA vaccines against SARS-CoV-2 is considerably lower than that of mRNA vaccines. A pyro-drive jet injector (PJI) efficiently delivers plasmid DNA intradermally into animal models. Here, we compared the immunogenic potential of DNA and mRNA vaccines in mice using the same platform. PJI was used to deliver naked mRNA and pDNA and their efficacy in inducing antigen expression and immune responses was assessed. Our results showed that PJI efficiently delivered mRNA into the skin, and a smaller effective dose than that of pDNA injection was required to achieve similar levels of antigen expression. The PJI-delivered CpG-free pDNA vaccine efficiently induced antigen-specific antibody production and a cell-mediated IFN-γ response compared to the mRNA vaccine, as well as the upregulation of inflammatory cytokines (IL-6, IFN-γ, and IL-1β) in the skin and lymph nodes. However, the intradermal mRNA vaccine was significantly less immunogenic than the standard intramuscular mRNA-lipid nanoparticle vaccine, despite equivalent mRNA dosages. Improvements in lipid nanoparticle and mRNA technology have revolutionized mRNA vaccines, and DNA vaccines can be similarly modified for higher clinical efficacy.