Comparison of efficacy of three recombinant adenoviruses expressing classical swine fever virus E2 proteins in rabbit model.

To obtain a good recombinant adenovirus,the present study evaluated the rAdV-E2 expressing E2 gene of classical swine fever virus(CSFV),rAdV-opti E2 encoding optimized CSFV E2 gene and rAdV-E2UL 49 encoding the CSFV E2gene fused with pseudorabies virus(PRV)UL49 gene encoding the VP22 protein of PRV in terms of antibody production,and protection of fever and virus replication following challenge in a rabbit model,respectively.Three out of five rabbits immunized with rAdV-E2UL49 produced CSFV-specific neutralizing antibodies on week 2 after immunization,whereas no specific neutralizing antibodies were detected in all those immunized with the other two recombinant adenoviruses.The antibody-blocking rate of rAdV-E2UL49-immunized rabbits reached 70% before challenge,and this was comparable to the rabbits immunized with C-strain.Following challenge,there were no fever reaction in the rabbits immunized with C-strain or rAdV-E2UL49,which were ob- served in the rabbits immunized with rAdV-E2(3/5),rAdV-optiE2(3/5)and wtAdV(5/5).Viral RNA was not detected by the real-time RT-PCR assay in all spleens from the rAdV-E2UL49-immunized and C-strain-immunized rabbits,but it was detected in those of the rabbits immunized with rAdV-E2(1/5),rAdV-optiE2(1/5)or wtAdV (5/5).The results showed that the rAdV-E2UL49might be a potential candidate vaccine against CSF.