CEA is a 180 kDa oncofetal glycoprotein and a well-known soluble tumor marker. Previously, we performed a phase I trial of cancer vaccine therapy using dendritic cells (DCs) pulsed with CEA specific peptide (CEA 652), whish was bound by HLA-A2402, for patients with colorectal cancer. The peripheral blood mononuclear cells from 3 of 4 patients after vaccinations showed HLA-A24 restricted and CEA-specific cytotoxic activity. However, no clinical responses were recognized (Cancer Immunol. Immunother., 53: 2004). Therefore, we have studies a gene-based vaccination strategy using DCs adenovirally transduced with whole tumor-associated antigen (TAA) gene. We demonstrated that the vaccination using DCs expressing simultaneously TAA and GM-CSF and IL-12 showed more efficient tumor suppression than vaccination using DCs expressing TAA alone in BALB/c mouse models (AACR proceedings, 2004). In this study, DCs were adenovirally transduced with CEA gene, GM-CSF gene and IL-12 gene at the same time, and it was examined whether the vaccination using these genetically engineered DCs could induce anti-tumor immunity against MC38-CEA in CEA transgenic mice. (Methods) (1) C57BL/6J-TgN(CEA Ge)18FJP (CEA Tg mice) (kindly provided by Dr. F. J. Primus) were immunized once by s.c. injection with genetically modified DCs. Spleen cells were isolated 14 days after immunization, and cultured without MC38-CEA in vitro for 3 days. Then, the spleen cells were assayed in a 51Cr-release assay. MC38-CEA and MC38-BGP and MC38 were used as target cells. (2) CEA Tg mice were inoculated subcutaneously with MC38-CEA. Five days after tumor inoculation, the mice were s.c. injected once with genetically modified DCs. Thirty-five days after treatment, the diameter of the subcutaneous tumor was estimated. (Results) The cytotoxic activity against MC38-CEA in mice immunized with DCs expressing CEA was significantly enhanced by double cotransduction both of IL-12 gene and GM-CSF gene (p<0.05). On the other hand, cytotoxic activity against MC38-BGP or MC38, which dose not express CEA, was very low in all groups. In the subcutaneous tumor models of MC38-CEA, the vaccination using DCs simultaneously expressing CEA, GM-CSF and IL-12 caused more remarkable inhibition of tumor growth than the vaccination using DCs expressing CEA alone (p<0.0001). Importantly, tumor-free mice were observed in these DCs vaccination group (4/5) on day 40. In conclusion, the vaccination using DCs simultaneously expressing CEA, IL-12 and GM-CSF may be useful for clinical application.

[Proc Amer Assoc Cancer Res, Volume 46, 2005]