Immunization with a bovine herpesvirus 1 glycoprotein B DNA vaccine induces cytotoxic T-lymphocyte responses in mice and cattle

Virus-specific cytotoxic T lymphocytes (CTLs) are considered to be important in protection against and recovery from viral infections. In this study, several approaches to induce cytotoxicity against bovine herpesvirus 1 (BHV-1) were evaluated. Vaccination of C57BL/6 mice with BHV-1 induced a strong humoral, but no CTL, response, which may be due to downregulation of major histocompatibility complex class I molecules. In contrast, vaccinia virus expressing glycoprotein B (gB) elicited a weaker antibody response, but strong cytotoxicity, in mice. As an approach to inducing both strong humoral and cellular immune responses, a plasmid vector was then used to express gB. Both antibody and CTL responses were induced by the plasmid encoding gB in C57BL/6 and C3H mice, regardless of the type of vector backbone. This demonstrated that DNA immunization induces a broad-based immune response to BHV-1 gB. Interestingly, removal of the membrane anchor, which resulted in secretion of gB from transfected cells, did not result in reduced cytotoxicity. Here, it is shown that, compared with the cell-associated counterpart, plasmid-encoded secreted protein may induce enhanced immune responses in cattle. Therefore, calves were immunized intradermally with pMASIAtgB, a plasmid encoding the secreted form of gB (tgB), using a needle-free injection system. This demonstrated that pMASIAtgB elicited both humoral responses and activated gamma interferon-secreting CD8+ CTLs, suggesting that a DNA vaccine expressing tgB induces a CTL response in the natural host of BHV-1.