Induction of SARS-nucleoprotein-specific immune response by use of DNA vaccine

Induction of effective cytotoxic T lymphocyte (CTL) and/or a specific antibody against conserved viral proteins may be essential to the development of a safe and effective severe acute respiratory syndrome coronavirus (SARS-Cov) vaccine. DNA vaccination represents a new strategy for induction of humoral and cellular immune response. To determine the ability of SARS-Cov nucleoprotein (N protein) to induce antiviral immunity, in this report, we established a stable C2C12 line expressing SARS-Cov N protein, which was used as a target for specific CTL assay. We also expressed recombinant N proteins in Escherichia coli and prepared N protein-specific polyclonal antibodies. C3H/He mice were immunized with N protein-expressible pcDN-fn vector by intramuscular injections. We found that the DNA vaccination induced both N protein-specific antibody and specific CTL activity to the target. When C3H/He mice were immunized by three separate injections, high antibody titre (1:3200–1:6400, average titre is 1:4580) and high CTL activity (67.4±8.4% (E:T=25:1), 69.6±6.7% (E:T=50:1) and 71.8±6.2% (E:T=100:1)) were observed. In the case of two vaccine injections, CTL activity was also high (56.6±12.7% (E:T=25:1), 57.4±11.7% (E:T=50:1) and 63.0±6.3% (E:T=100:1)). However, antibody titres were much lower (1:200–1:3200, average titre is 1:980). Our results suggest that SARS-Cov nucleocapsid gene might be a candidate gene for SARS DNA vaccination.