A West Nile virus DNA vaccine induces neutralizing antibody in healthy adults during a phase 1 clinical trial

Background. West Nile virus (WNV) is a mosquitoborne flavivirus that can cause severe meningitis and encephalitis in infected individuals. We report the safety and immunogenicity of a WNV DNA vaccine in its first phase 1 human study. Methods. A single-plasmid DNA vaccine encoding the premembrane and the envelope glycoproteins of the NY99 strain of WNV was evaluated in an open-label study in 15 healthy adults. Twelve subjects completed the 3-dose vaccination schedule, and all subjects completed 32 weeks of evaluation for safety and immunogenicity. The development of a vaccine-induced immune response was assessed by enzyme-linked immunosorbant assay, neutralization assays, intracelluar cytokine staining, and enzyme-linked immunospot assay. Results. The vaccine was safe and well tolerated, with no significant adverse events. Vaccine-induced T cell and antibody responses were detected in the majority of subjects. Neutralizing antibody to WNV was detected in all subjects who completed the 3-dose vaccination schedule, at levels shown to be protective in studies of horses, an incidental natural host for WNV. Conclusions. Further assessment of this DNA platform for human immunization against WNV is warranted.