Vaccination with naked
DNA may be an alternative to conventional
vaccines because it combines the efficacy of
attenuated vaccines with the
biological safety of
inactivated vaccines. We recently showed that the vaccination with naked
DNA coding for the immunorelevant
glycoprotein D (gD) of pseudorabies virus (PRV) induced both antibody and cell-mediated immunity in pigs and provided protection against challenge
infection. To determine whether the efficacy of the naked
DNA vaccination against PRV could be improved, we compared three sets of variables. First, the efficacy of the
naked DNA vaccine coding only for the immunorelevant gD was compared with a cocktail
vaccine containing additional plasmids coding for two other immunorelevant
glycoproteins, gB and gC. Second, the intramuscular route of vaccination was compared with the intradermal route. Third, the commonly used needle method of inoculation was compared with the needleless Pigjet injector method. Five groups of five pigs were vaccinated three times at 4-weeks intervals and challenged with the virulent NIA-3 strain of PRV 6 weeks after the last vaccination. Results showed that although the cocktail
vaccine induced stronger cell-mediated immune responses than the
vaccine containing only gD plasmid, both
vaccines protected pigs equally well against challenge
infection. Intradermal inoculation with a needle induced significantly stronger antibody and cell-mediated immune responses and better protection against challenge
infection than intramuscular inoculation. Our data show that the route of administering
DNA vaccines in pigs is important for an optimal induction of protective immunity.