One-time gene gun or intramuscular rabies DNA vaccination of non-human primates: comparison of neutralizing antibody responses and protection against rabies virus 1 year after vaccination.

We have previously shown that Macaca fascicularis (Cynomologus) monkeys receiving a primary and either one or two booster rabies DNA vaccinations are protected against rabies virus. In this study, we determined whether monkeys that had been vaccinated only once via gene gun or intramuscularly (i.m.) with different concentrations of DNA would be protected against rabies virus challenge. Neutralizing antibody responses were assayed for 1 year before the monkeys were challenged. Neutralizing antibody was detected at least 50 days earlier in gene gun vaccinated as compared to i.m. vaccinated animals. Prior to viral challenge, all (6/6, 100%) gene gun vaccinated animals, but only 3/6 (50%) i.m. vaccinated animals seroconverted. In general, antibody titers of the gene gun vaccinated animals were higher than the titers of the i.m. vaccinated animals. There was no correlation between the concentration of DNA used for vaccination, the neutralizing antibody responses elicited and protection against viral challenge. Seven days after viral challenge, a rapid and strong anamnestic antibody response was elicited in 100% of the gene gun vaccinated monkeys and in four i.m. vaccinated monkeys. Neutralizing antibody remained undetectable in two i.m. vaccinated monkeys. Overall, 60% (3/5) of the gene gun vaccinated animals and 87% (5/6) of the i.m. vaccinated monkeys survived viral challenge. This study is the first, to our knowledge, to show long-term protection of non-human primates against a human viral pathogen using a DNA vaccination protocol that did not include a booster immunization.