Priming with DNA encoding E2 and boosting with E2 protein formulated with CpG oligodeoxynucleotides induces strong immune responses and protection from Bovine viral diarrhea virus in cattle

The objective of this study was to develop an optimal vaccination strategy forBovine 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-tPAsΔE2). Furthermore, a pure secreted recombinant ΔE2 (rΔE2) protein was produced. The rΔE2 protein was formulated with a combination of Emulsigen and CpG oligodeoxynucleotide. Groups of calves were immunized with pMASIA-tPAsΔE2 or with rΔE2, or first with pMASIA-tPAsΔE2 and then with rΔE2. 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 ΔE2 DNA-primed calves with rΔE2 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.