Development and evaluation of a replicon particle vaccine expressing the E2 glycoprotein of bovine viral diarrhea virus (BVDV) in cattle

Abstract

Background: Bovine viral diarrhea virus is one of the most significant and costly viral pathogens of cattle worldwide. Alphavirus-derived replicon particles have been shown to be safe and highly effective vaccine vectors against a variety of human and veterinary pathogens. Replicon particles are non-propagating, DIVA compatible, and can induce both humoral and cell mediated immune responses. This is the first experiment to demonstrate that Alphavirus-based replicon particles can be utilized in a standard prime/boost vaccination strategy in calves against a commercially significant bovine pathogen.

Findings: Replicon particles that express bovine viral diarrhea virus sub-genotype 1b E2 glycoprotein were generated and expression was confirmed in vitro using polyclonal and monoclonal antibodies specific to E2. Vaccine made from particles was generated in Vero cells and administered to BVDV free calves in a prime/boost regimen at two dosage levels. Vaccination resulted in neutralizing antibody titers that cross-neutralized both type 1 and type 2 BVD genotypes following booster vaccination. Additionally, high dose vaccine administration demonstrated some protection from clinical disease and significantly reduced the degree of leukopenia caused by viral infection.

Conclusions: Replicon particle vaccines administered in a prime/boost regimen expressing BVDV E2 glycoprotein can induce cross-neutralizing titers, reduce leukopenia post challenge, and mitigate clinical disease in calves. This strategy holds promise for a safe and effective vaccine to BVDV.

Figure 1

Indirect immunofluorescence assay of replicon particle (RP) infected Vero cells. Vero cell monolayers were infected with RP expressing either (A) the E2 glycoprotein gene of BVDV subgenotype 1b strain NY1 or (B) a non-BVDV-derived gene as a control. Cells were fixed and subsequently stained with a monoclonal antibody specific to BVDV 1b E2 and a fluorescent-conjugated anti-mouse secondary antibody.

Figure 2

Geometric mean of viral neutralizing antibody dilutions on day of virus challenge. The 1×10⁷ IU vaccinated group had significantly higher geometric mean VN titers (P=.04 by oneway ANOVA) than the 1×10⁶ IU dosage level. Reference strains used were Singer (type 1) and 296c (type 2).

Figure 3

Y-axis is percent depletion of circulating white blood cells when compared to pre-challenge baseline (set to 100%). The highest levels of depletion were seen in the placebo groups with a dose dependent decrease in WBC reduction in vaccinated groups. Error bars indicate standard error from mean percentage depletion.

Figure 4

Mean rectal temperatures (°F) post challenge with BVD1b NY1 (Y-axis.) X-axis is days post viral challenge. Error bars indicate standard error from mean.

Figure 5

Mean clinical scores over the course of the study. Scores were based on presence of mild nasal discharge, mild ocular discharge, or mild depression. No differences were seen in clinical outcomes between low dose E2 RP and placebo controls in clinical disease.