Characterization of a messenger RNA polynucleotide vaccine vector.

We have constructed mRNA transcripts encoding luciferase and human carcinoembryonic antigen (CEA) which are capped, polyadenylated, and stabilized by human beta-globin 5' and 3' untranslated regions. The mRNA construct encoding human CEA directed CEA expression in mouse fibroblasts in vitro following liposome-mediated transfection. The luciferase encoding mRNA transcripts mediated luciferase expression in vivo following i.m. injection. Based on the demonstration of protein expression in vitro and in vivo, the feasibility of using such a vector as a tumor vaccine was examined. In this pilot study, seven mice received 50 micrograms mRNA transcripts encoding CEA twice weekly for 5 weeks by i.m. injection followed by challenge with syngeneic, CEA-expressing tumor cells. This dose and schedule "primed" an immune response to CEA. Five of seven mRNA-immunized mice demonstrated anti-CEA antibody 3 weeks after tumor challenge whereas control mice had no evidence of antibody response. This strategy might be particularly useful to induce an immune response to a proto-oncogene product or growth factor which poses a risk of inducing malignant transformation consequent to prolonged protein expression.