Targeting improves the efficacy of a DNA vaccine against Corynebacterium pseudotuberculosis in sheep.

A large-scale DNA vaccination trial was performed with sheep to investigate whether an antigen targeted by CTLA-4 enhanced and accelerated the humoral immune response. Vaccination with genetically detoxified phospholipase D (DeltaPLD) has been shown to be effective, at least partially, against Corynebacterium pseudotuberculosis, the causal agent of caseous lymphadenitis in sheep. CTLA-4 binds to B7 on antigen-presenting cells and thus was used to direct the fusion antigens to sites of immune induction. Here we demonstrated that targeting DeltaPLD as a CTLA-4 fusion protein significantly enhanced the speed, magnitude, and longevity of the antibody response compared to that obtained with DNA encoding DeltaPLD. While all groups of sheep vaccinated with DNA encoding DeltaPLD were afforded better protection against an experimental challenge with C. pseudotuberculosis than those immunized with an irrelevant plasmid or those left unimmunized, the best protection was provided by the targeted DNA vaccine. We propose that targeting antigens to antigen-presenting cells offers a generic strategy for enhancing the efficacy of DNA vaccines.