Immunogenicity of a recombinant adenovirus expressing porcine reproductive and respiratory syndrome virus polyepitopes

The objective of this work was to evaluate the immunogenicity of a chimeric antigen containing characterized PRRSV epitopes. A synthetic gene, designated HEJ, encoding defined epitopes was used to generate a recombinant adenovirus designed Ad-HEJ. The chimeric antigen included T-cell epitopes from structural and nonstructural proteins, and a neutralizing B-cell epitope. Following a homologous prime-boost immunization, the Ad-HEJ virus elicited significant (p < 0.05) epitope-specific IFN-γ responses compared to sham-treatment. Two weeks post-challenge, this response was significantly (p < 0.05) higher compared to the negative control treatment. IFN-γ response to PRRSV stimulation in vitro were observed in both groups only after challenge. Antibodies against PRRSV and peptides were detectable following prime-boost immunization in the Ad-HEJ treatment group and the responses increased post-challenge against the virus and against most of the peptides. All the swine were viremic one week post-challenge, but four weeks later, five out of the seven Ad-HEJ vaccinees had cleared the PRRSV, whereas only two of the six negative controls had cleared the virus. The outcome suggests that the adenovirus expressing defined epitopes induced a strong immune response against the peptides, but this response was not sufficient to confer protection against PRRSV challenge.