Therapeutic tumor immunity induced by polyimmunization with melanoma antigens gp100 and TRP-2

To improve the immunogenicity of melanoma self-antigens, we used a novel strategy of nonviral genetic vaccination coupled with muscle electroporation. Electroporation-enhanced immunization with plasmids encoding either human gp100 or mouse TRP-2 antigens induced only partial rejection of B16 melanoma challenge. However, immunization with a combination of these two antigens caused tumor rejection in 100% of the immunized mice. Splenocytes from combination-immunized animals killed syngeneic targets loaded with peptides derived from both gp100 and TRP-2. Immune cell depletion experiments identified CD8+ T lymphocytes as the primary effectors of antitumor immunity. Most importantly, polyimmunization led to the generation of a therapeutic immune response that significantly improved the mean survival time of mice bearing established lung metastases. These results validated the usefulness of electroporation-enhanced, nonviral genetic immunization for the active immunotherapy of cancer and indicated that using a combination of different tumor antigens may be a decisive strategy for a successful therapeutic vaccination.