A subunit gIV vaccine, produced by transfected mammalian cells in culture, induces mucosal immunity against bovine herpesvirus-1 in cattle

A truncated version of bovine herpesvirus-1 (BHV-1) glycoprotein 1 V (tgIV V) was produced in a novel, non-destructive expression system based upon regulation of gene expression by the bovine heat-shock protein 70A (hsp70) gene promoter in Madin Dal-by bovine kidney (MDBK) cells. In this system, up to 20 μg ml −1 of secreted tgIV, which is equivalent to the yield from 4 × 10 6 cells, was produced daily over a period of up to 18 days. Different doses of tgIV were injected intramuscularly into seronegative calves. Virus-neutralizing antibodies were induced by all doses of tgIV, both in the serum and in the nasal superficial mucosa. However, the low dose (2.3 μg) induced significantly ( p < 0.05) lower antibody titres than the medium (7 μg) and high (21 μg) doses. The medium and high doses of tgIV conferred protection from BHV-1 infection, as demonstrated by a significant ( p < 0.05) reduction in clinical signs of respiratory disease and virus shedding in the nasal secretions postchallenge. However, the 2.3,ug group, although partially protected, was not significantly ( p > 0.05) different from the placebo group. This study demonstrated the potential of an intramuscularly administered tgIV subunit vaccine to induce mucosal immunity to BHV-1 using an economic protein production system and an acceptable vaccine formulation. In addition, a strong correlation was observed between neutralizing antibodies in the serum and nasal superficial mucosa, virus shedding and clinical disease. Thus, serum neutralizing antibody levels in tgIV-immunized animals may be a good prognosticator of protection from BHV-1 infection and disease.