Mice vaccination with interleukin 12-transduced colon cancer cells potentiates rejection of syngeneic non-organ-related tumor cells

Cell-based gene therapy after cytokine gene transfer is being investigated for autologous and allogeneic vaccination in cancer therapy. Here we show that mice vaccinated with 3-5 x 10(6) interleukin 12 (IL-12) gene-transduced CT26 colon cancer cells developed a long-lasting antitumor immune memory able to reject not only parental cells but also syngeneic, LM3 mammary, and MCE fibrosarcoma tumorigenic cells. In contrast, mice vaccinated with 0.5-1 x 10(6) CT26 cells transduced with pBabe neo IL-12 retrovirus cells (CT26-IL12) were only able to reject parental cells. An increase in the total circulating levels of IgG2a and a clear shift toward a systemic Th1 response developed, regardless of the amount of injected CT26-IL12 cells. On the contrary, a strong increase in anti-CT26-specific IgG2a levels was observed only when 3-5 x 10(6) CT26-IL12 cells were injected. Immunocompetent mice vaccinated with 3-5 x 10(6) CT26-IL12 cells developed local nodules for a few days, which then ceased growing. These nodules comprised mainly blood vessels, suggesting that an angiogenic process was taking place. CD8+ T cells were responsible for the anti-LM3 tumor cell memory, whereas CD4+ T cells were not involved. Splenocytes and lymphocytes obtained from mice immunized against CT26 cells were able to kill LM3 cells in vitro. Adoptive transfer of lymphocytes obtained from animals immunized against CT26 colon cancer cells suppressed LM3 mammary tumor growth in tumor-bearing mice. The present studies raised the possibility of isolating CTL clones and identifying CTL epitopes shared by different tumor cell types, which can be a target for cancer therapy.