We have previously shown that TS/A murine mammary adenocarcinoma cells, induced to express high surface expression of MHC class II molecules by stable transfection of CIITA, resulted in high rate (92%) of tumor rejection and tumor immunity to subsequent homologous tumor challenges. The immunological basis of tumor response is based on tumor-specific CD4(+) T helper type 1 (Th1) in the priming phase and tumor-specific CD8(+) T cells as the major effector cells. IL-12 is the crucial cytokine that drives Th1 polarization in conjunction with inducing strong cellular-based immune responses. We have previously shown in the same tumor model that a naked DNA IL-12 gene transfer was effective in preventing tumor angiogenesis in an immunopreventive approach when administrated at least 2 days prior to the tumor inoculation. Here we indicate that the combination of the two approaches in immunotherapy of established tumors is efficacious in delaying tumor growth but not in completely eradicating the tumor.