Nucleic acid vaccination against virally induced tumors

Plasmid DNA (pSV3-neo) encoding the large tumor antigen (T-ag) of simian virus 40 (SV40) was used to actively immunize mice to assess the induction of SV40 T-ag specific immunity. Mice were injected with naked DNA intramuscularly, and both the cellular and humoral immune responses were compared to those elicited in mice immunized with recombinant protein. Administration of recombinant SV40 T-ag elicited high titer antibodies reactive with SV40 T-ag, whereas inoculation with DNA failed to generate comparable levels of SV40 T-ag specific antibody. Conversely, antigen specific cytotoxic T lymphocyte activity was generated in mice immunized with pSV3-neo, but was not detected in mice immunized with the recombinant protein. Moreover, the cellular immunity generated by the injection of pSV3-neo DNA was protective against a lethal challenge with syngeneic SV40 transformed cells. Together, these data indicate that active immunization with genes encoding tumor specific antigens may be an efficacious strategy for the induction of cell-mediated mechanism(s) to prevent cancer.