DNA vaccines combine remarkable genetic and chemical stability with proven safety and efficacy in animal models, while remaining less immunogenic in humans. In contrast, live-
attenuated vaccines have the advantage of inducing rapid, robust, long-term immunity after a single-dose vaccination. Here we describe novel iDNA
vaccine technology that is based on an infectious
DNA platform and combines advantages of
DNA and live
attenuated vaccines. We applied this technology for vaccination against
infection with Venezuelan equine encephalitis virus (VEEV), an alphavirus from the Togaviridae family. The iDNA
vaccine is based on transcription of the full-length genomic
RNA of the TC-83 live-attenuated virus from plasmid
DNA in vivo. The in vivo-generated
viral RNA initiates limited replication of the
vaccine virus, which in turn leads to efficient immunization. This technology allows the plasmid
DNA to launch a live-
attenuated vaccine in vitro or in vivo. Less than 10 ng of pTC83 iDNA encoding the full-length genomic
RNA of the TC-83
vaccine strain initiated replication of the
vaccine virus in vitro. In order to evaluate this approach in vivo, BALB/c mice were vaccinated with a single dose of pTC83 iDNA. After vaccination, all mice seroconverted with no adverse reactions. Four weeks after immunization, animals were challenged with the lethal epidemic strain of VEEV. All iDNA-vaccinated mice were protected from fatal disease, while all unvaccinated controls succumbed to
infection and died. To our knowledge, this is the first example of launching a clinical live-
attenuated vaccine from recombinant plasmid
DNA in vivo.