Protection of chickens against reticuloendotheliosis virus infection by DNA vaccination

The present study was undertaken to evaluate the ability of DNA vaccination to protect chickens against reticuloendotheliosis virus (REV) infection and to determine whether codon optimization and the woodchuck hepatitis virus posttranscriptional regulatory element (WPRE) could improve the immunogenicity of the DNA vaccines. The wild-type and codon-optimized gp90 genes of REV were cloned into pCAGGS vector, and designated as pCAGgp90 and pCAGoptigp90, respectively. Plasmids pCAGWgp90 and pCAGWoptigp90 containing WPRE were also constructed. To evaluate vaccine efficacy, 3-week-old specific pathogen free chickens were injected with the constructed plasmids twice at 3-week intervals and challenged with REV 3 weeks post boost. Plasmids pCAGoptigp90 and pCAGWgp90 elicited significantly higher humoral and cellular immune responses than pCAGgp90, while chickens immunized with pCAGWoptigp90 showed the highest immune responses among the groups. Chickens immunized with pCAGgp90, pCAGoptigp90, pCAGWgp90 or pCAGWoptigp90 had 53%, 67%, 73% or 87% protection, respectively, as evidenced by the absence of REV viremia, while the empty vector pCAGGS only conferred 13% protection against viremia. These results highlight the potential value of DNA vaccination in the prevention of REV infection and suggest that codon optimization and WPRE could increase the efficacy of DNA vaccines.