Induction of murine ras oncogene peptide-specific T cell responses by immunization with plasmid DNA-based minigene vectors.

In a BALB/c mouse model, we have previously identified a ras oncogene peptide that contained both CD8(+) and CD4(+) T cell epitopes in a nested configuration. In this study, we developed several plasmid DNA minigene vectors encoding these determinants and examined whether they could induce antigen (Ag)-specific CD8(+) cytotoxic and CD4(+) lymphoproliferative responses. Furthermore, we compared two different immunization procedures, epidermal gene gun inoculation and intradermal (i.d.) injection of saline plasmid DNA, along with several approaches addressing different aspects of immune modulation. We demonstrated that each DNA plasmid induced the relevant Ag-specific cellular immune response. Gene gun inoculation was superior to that of needle injection for induction of the CTL response. Moreover, DNA plasmids containing both ras epitopes induced the highest CTL response, as compared with vector preparations containing only the CD8(+) epitope. These results suggested that a DNA plasmid expressing nested mutant ras epitope-specific CD4(+) and CD8(+) T cell epitopes can be processed in vivo to induce both subset-specific T cell responses, and that the addition of the helper epitope quantitatively improved the development of the CTL response, which may have implications for DNA-based anti-tumor immunotherapies.