Comprehensive evaluation of the adenovirus/alphavirus-replicon chimeric vector-based vaccine rAdV-SFV-E2 against classical swine fever

Classical swine fever (CSF) is an economically important, highly contagious swine disease caused by classical swine fever virus (CSFV). Marker vaccines and companion serological diagnostic tests are thought to be a promising strategy for future control and eradication of CSF. Previously, we have demonstrated that an adenovirus-vectored Semliki forest virus replicon construct expressing the E2 glycoprotein from CSFV, rAdV-SFV-E2, induced sterile immunity against a lethal CSFV challenge. In this study, we further evaluated the vaccine with respect to its safety, number and dose of immunization, and effects of maternally derived antibodies, re-immunization of the vaccine or co-administration with pseudorabies vaccine on the vaccine efficacy. The results showed that: (1) the vaccine was safe for mice, rabbits and pigs; (2) two immunizations with a dose as low as 6.25 × 10⁵ TCID₅₀ or a single immunization with a dose of 10⁷ TCID₅₀ rAdV-SFV-E2 provided complete protection against a lethal CSFV challenge; (3) maternally derived antibodies had no inhibitory effects on the efficacy of the vaccine; (4) the vaccine did not induce interfering anti-vector immunity; and (5) co-administration of rAdV-SFV-E2 with a live pseudorabies vaccine induced antibodies and protection indistinguishable from immunization with either vaccine administered alone. Taken together, the chimeric vaccine represents a promising marker vaccine candidate for control and eradication of CSF.