CTL RESPONSE AND PROTECTION AGAINST P815 TUMOR CHALLENGE IN MICE IMMUNIZED WITH DNA EXPRESSING THE TUMOR-SPECIFIC ANTIGEN P815A

A DNA immunization approach was used to induce an immune response agai nst the tumor-specific antigen P815A in DBA/2 mice, The PIA gene, whic h encodes the P815A antigen, was modified by the addition of a short s equence coding for a tag epitope recognized by the monoclonal antibody AU1, and cloned into the eukaryotic expression vector pBKCMV, resulti ng in plasmid pBKCMV-P1A. L1210 cells stably transfected with pBKCMV-P 1A expressed P1A mRNA and were lysed by the syngeneic P815A-specific c ytotoxic clone CTL-P1:5, thus confirming that the tag-modified P1A pro tein underwent correct processing and presentation. A single intramusc ular injection of 100 mu g of pBKCMV-P1A induced the expression of P1A mRNA for at least 4 months, Eighty percent of DBA/2 mice injected thr ee times with 100 mu g of pBKCMV-P1A generated cytotoxic T lymphocytes (CTL) that lysed P815 tumor cells, whereas mock-inoculated animals fa iled to show any cytotoxicity, Moreover, experiments designed to evalu ate the protection of pBKCMV-P1A-immunized mice against a lethal chall enge with P815 tumor cells showed that 6 of 10 immunized mice rejected the tumor, and 2 mice showed prolonged survival compared to control a nimals.