Critical role for DNA vaccination frequency in induction of antigen-specific cytotoxic responses.

Since antigen-persistence plays a role for induction of immunity, we investigated the in vivo pharmacokinetic of a naked DNA vaccine at the site of its action, i.e., in the lymph node. After direct intralymphatic injection, naked DNA vaccine degraded within a few hours. In correlation with the short persistence of the DNA vaccine we found that the frequency of vaccination critically influenced the strength of the immune response. In mice vaccinated every 3 days, cytotoxic T-cell responses were enhanced compared to immunization in 6 or 9 days intervals. The results suggest that the so far disappointing efficiency of naked DNA vaccines in humans may be overcome by more frequent vaccination.