Rabies DNA vaccine in the horse: strategies to improve serological responses

In order for DNA vaccines to become a practical alternative to conventional vaccines their ability to induce antibody responses in large mammals needs to be improved. We used DNA vaccination against rabies in the horse as a model to test the potential of two different strategies to enhance antibody responses in a large mammalian species. The administration of the DNA vaccine in the presence of aluminum phosphate improved both the onset and the intensity of serological responses but was not potent enough to achieve seroconversion in all vaccinated ponies. However, when the DNA vaccine was formulated with the cationic lipid DMRIE–DOPE instead of aluminum phosphate, a very strong impact on both onset and intensity of serological responses was observed. This latter strategy ensured excellent seroconversion in all vaccinated ponies after a primary course of two injections, demonstrating a clear improvement of the homogeneity of the induced responses. These data indicate that rabies DNA vaccination is feasible in horses and further suggests that properly formulated DNA vaccines can generate immune responses in large veterinary species at a level comparable to the responses achieved with conventional vaccines.