The objective of this study was to develop an optimal vaccination strategy for Bovine viral
diarrhea virus (BVDV). The E2
protein of BVDV plays a major protective role against BVDV
infection. In order to be able to compare
DNA,
protein and
DNA prime-
protein boost regimens, a plasmid was constructed encoding a secreted form of the NADL strain E2
protein (pMASIA-tPAsDeltaE2). Furthermore, a pure secreted recombinant DeltaE2 (rDeltaE2)
protein was produced. The rDeltaE2
protein was formulated with a combination of Emulsigen and CpG
oligodeoxynucleotide. Groups of calves were immunized with pMASIA-tPAsDeltaE2 or with rDeltaE2, or first with pMASIA-tPAsDeltaE2 and then with rDeltaE2. To evaluate the protection against BVDV, calves were challenged with BVDV strain NY-1 after the last immunization. Although all immunized calves developed humoral and cellular immune responses, the antibody responses in the
DNA prime-
protein boost group were stronger than those elicited by either the
DNA vaccine or the
protein vaccine. In particular, E2-specific antibody titres were enhanced significantly after boosting the DeltaE2
DNA-primed calves with rDeltaE2
protein. Moreover, protection against BVDV challenge was obtained in the calves treated with the
DNA prime-
protein boost vaccination regimen, as shown by a significant reduction in
weight loss, viral excretion and
lymphopenia, compared with the unvaccinated calves and the animals immunized with the
DNA or
protein only. These results demonstrate the advantage of
a DNA prime-
protein boost vaccination approach in an outbred species.