Protective efficacy of a dengue 2 DNA vaccine in mice and the effect of CpG immuno-stimulatory motifs on antibody responses

A recently described DNA vaccine for dengue (DEN) type 2 was shown to elicit high levels of neutralizing antibodies in mice. The vaccine candidate consists of the PreM and 92% of the envelope genes of DEN 2 New Guinea C strain. We further evaluated this DNA vaccine candidate by examining the effect of immuno-stimulatory CpG DNA motifs on antibody response and by studying the protective efficacy of the vaccine. The results showed that CpG motifs present in pUC 19 significantly improved the antibody response to a suboptimal dose of 3.1 μg of the DEN DNA vaccine. In a lethal mouse intracerebral challenge model, the vaccine provided a significant level of protection. Sixty percent of the mice immunized with the DEN DNA vaccine plus pUC 19 survived the challenge compared to only 10% in the control group that received vector plus pUC. These studies illustrate that nucleic acid immunization is a viable approach to developing a DEN vaccine and that immuno-stimulatory CpG DNA motifs can be used to lower the minimum dose required to produce an antibody response.