Immune responses with DNA vaccines encoded different gene fragments of severe acute respiratory syndrome coronavirus in BALB/c mice

To analyze the immune responses of DNA vaccine encoded different gene fragments of severe acute respiratory syndrome coronavirus (SARS-Cov), SARS-Cov gene fragments of membrane (M), nucleocapsid (N), spike a (Sa), and spike b (Sb) proteins were cloned into pcDNA3.1 (Invitrogen) vector to form plasmids pcDNAM, pcDNAN, pcDNASa, and pcDNASb, respectively. After mice were immunized intramuscularly with pcDNAM, pcDNAN or pcDNASa–pcDNASb plasmid, blood was collected and serum was separated. Humoral immune response was detected with the enzyme-linked immunosorbent assay, and cellular immune response of SARS-Cov DNA vaccines was detected with lymphoproliferation assay and cytotoxic T lymphocyte assay. Results show that cellular and humoral immune responses can be detected after immunization with pcDNAM, pcDNAN or pcDNASa–pcDNASb plasmids in BALB/c mice. However, pcDNAM stimulated the highest cellular immune response than other plasmids, and pcDNASa–pcDNASb stimulated the highest humoral immune response in week 12. The present results not only suggest that DNA immunization with pcDNAM, pcDNAN or pcDNASa–pcDNASb could be used as potential DNA vaccination approaches to induce antibody in BALB/c mice, but also to illustrate that gene immunization with these SARS DNA vaccines different immune response characters.