Immunization with SARS-CoV S DNA vaccine generates memory CD4+ and CD8+ T cell immune responses

An effective vaccine for severe acute respiratory syndrome (SARS) will probably require the generation and maintenance of both humoral and cellular immune responses. It has been reported that after natural infection in humans and immunization in animals with SARS-CoV vaccine, antibody is produced and persistent for a long period of time. In the present study, mice were immunized i.m. with SARS-CoV S DNA vaccine, and three different methods (ELISA, ELISPOT and FACS) were used to evaluate the immune responses when the cells were stimulated in vitro with a pool of peptides overlapping entire SARS spike protein. The results show that prime-immunization with SARS-CoV S DNA vaccine can induce both CD4(+) and CD8(+) T cell responses. Boosting with the same vaccine enhances CD4(+) and CD8(+) T cell responses in both lymphoid and nonlymphoid organs and were persistent over two months. The SARS-CoV S-specific CD4(+) and CD8(+) T cells were CD62L(-), a marker for memory cells, and -30 to 50% of the cells expressed IL-7Ralpha (CD127), a marker for the capacity of effector cells to develop into memory cells. In addition, immunization with the DNA vaccine elicited high levels of antibody production. Taken together, these data demonstrate that immunization with SARS-CoV S DNA vaccine can generate antigen-specific humoral and cellular immune responses that may contribute to long-term protection.