Modification of CEA with both CRT and TAT PTD induces potent anti-tumor immune responses in RNA-pulsed DC vaccination

Carcinoembryonic antigen (CEA) is expressed on human colon carcinomas, is well characterized, and continues to be a promising target for cancer immunotherapy in humans. To enhance the immunogenecity of CEA, we developed a fusion gene (CRT-TAT-ΔCEA) of the TAT protein transduction domain (PTD) and calreticulin (CRT) with human CEA devoid of its signal sequences (ΔCEA) and evaluated anti-tumor immunity using RNA-pulsed dendritic cell (DC) vaccination. Mice vaccinated with DC by electroporation with mRNA encoding TAT-ΔCEA (DC/TAT-ΔCEA) and CRT-ΔCEA (DC/CRT-ΔCEA) had enhanced induction of tumor-specific cytotoxic T lymphocyte (CTL) and increased numbers of IFN-γ-secreting T cells by ELISPOT, as compared to mice vaccinated with DC/ΔCEA. DC/CRT-ΔCEA and DC/TAT-ΔCEA vaccines preferentially stimulated CD4⁺ and CD8⁺ T cells, respectively. The DC vaccine by electroporation with mRNA encoding CRT-TAT-ΔCEA (DC/CRT-TAT-ΔCEA) enhanced both CD4⁺ and CD8⁺ T cells. DC/CRT-TAT-ΔCEA had the additional effects of CRT and TAT PTD and enhanced the anti-tumor effect against CEA-expressing tumors compared to DC/CRT-ΔCEA or DC/TAT-ΔCEA. These findings suggest that modification of CEA with both CRT and TAT PTD induces potent anti-tumor immune responses in RNA-pulsed DC vaccination and may be a useful approach for DC-based immunotherapy.