Immunization with plasmid DNA encoding a truncated, secreted form of the bovine viral diarrhea virus E2 protein elicits strong humoral and cellular immune responses

The major protective antigen of bovine viral diarrhea virus (BVDV), the E2 protein, is cell-associated and not expressed on the cell surface. In this study we evaluated a DNA vaccine encoding various secreted versions of E2. In vitro analysis demonstrated that deletion of the transmembrane anchor and addition of the signal sequence of bovine herpesvirus-1 (BHV-1) (gDsΔE2) resulted in efficient secretion of E2 into the culture medium. In contrast, full-length E2, either without or with gDs (gDsE2), as well as truncated E2 without gDs (ΔE2), remained entirely cell-associated. Mice immunized with plasmid encoding gDsΔE2 developed significantly higher IgG and virus neutralizing antibody titres compared to animals vaccinated with plasmid encoding E2, ΔE2 or gDsE2. To optimize secretion of E2, the efficiency of gDs was compared with that of the tissue plasminogen activator signal (tPAs) sequence. In addition, the effect of the plasmid backbone was assessed by comparing two vectors. Four plasmids, pMASIA-gDsΔE2, pMASIA-tPAsΔE2, pSLKIA-gDsΔE2 and pSLKIA-tPAsΔE2, were constructed and administered intradermally to mice. The mice immunized with pMASIA-tPAsΔE2 developed the strongest and most balanced immune responses. Vaccination of cattle confirmed that pMASIA-tPAsΔE2 elicited both strong humoral and cellular immune responses and thus could be a candidate DNA vaccine against BVDV.