The protective immune response against Pseudorabies virus induced by DNA vaccination is impaired if the plasmid harbors a functional Porcine circovirus type 2 rep and origin of replication.

A plasmid rendered replicative in mammalian cells by inserting the Porcine circovirus 2 (PCV2) origin of replication and replicase gene (Ori-rep) has been previously constructed. The aim of the present study was to evaluate if the replication capacity of this plasmid could be advantageously used to improve the protective immunity induced by DNA vaccination. In this case we used the porcine Pseudorabies virus (PrV) DNA vaccination model. The replicative capacity of the DNA vaccine did not improve the protective immunity against PrV in pigs, but on the contrary the presence of the PCV2 Ori-rep sequence was harmful in the induction of this immunity compared to an equivalent but non-replicative DNA vaccine. In addition, the distribution and the persistence of the replicative and non-replicative plasmids inside the body were the same. This is the first study showing an in vivo deleterious effect of the replicative active PCV2 Ori-rep on the natural and specific protection against PrV infection.