Responses of Mice Immunized with a DNA Vaccine Encoding Carcinoembryonic Antigen (CEA)

C57BL/6 and BALB/c mice were immunized with two different plasmids (p91023B and pKCEA66) encoding different forms of the tumor-associated antigen carcinoembryonic antigen (CEA). The wild type form of CEA (p91023B), which is expressed at the cell surface, induces stronger anti-CEA IgG response after DNA-plasmid immunizations than the modified intracellular form of CEA (pKCEA66), which was designed to mount strong cellular responses. Boosting with recombinant CEA (rCEA) increased the anti-CEA IgG response significantly. In the tumor protection model used, where SCID mice are challenged with human tumor cells mixed with splenocytes from immunized mice, both innate and specific immune responses are responsible for the protective effect.