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 against the tumor-specific antigen P815A in DBA/2 mice. The P1A gene, which encodes the P815A antigen, was modified by the addition of a short sequence coding for a tag epitope recognized by the monoclonal antibody AU1, and cloned into the eukaryotic expression vector pBKCMV, resulting in plasmid pBKCMV-P1A. L1210 cells stably transfected with pBKCMV-P1A expressed P1A mRNA and were lysed by the syngeneic P815A-specific cytotoxic clone CTL-P1:5, thus confirming that the tag-modified P1A protein underwent correct processing and presentation. A single intramuscular injection of 100 μg of pBKCMV-P1A induced the expression of P1A mRNA for at least 4 months. Eighty percent of DBA/2 mice injected three times with 100 μg of pBKCMV-P1A generated cytotoxic T lymphocytes (CTL) that lysed P815 tumor cells, whereas mock-inoculated animals failed to show any cytotoxicity. Moreover, experiments designed to evaluate the protection of pBKCMV-P1A-immunized mice against a lethal challenge with P815 tumor cells showed that 6 of 10 immunized mice rejected the tumor, and 2 mice showed prolonged survival compared to control animals.

Overview summary

The murine P1A gene, which codes for the tumor-specific antigen P815A, was cloned into a eukaryotic expression vector and employed to evaluate the feasibility of a DNA immunization approach in a physiological model that closely resembles human cancer. The DNA immunization procedure resulted in cytotoxic T lymphocyte generation and protection against a lethal challenge with tumor cells expressing the relevant antigen.