A method is provided for inducing or enhancing an immune response in a mammal to a target polypeptide expressed in a plurality of cells of the mammal, which method comprises administering to the mammal an inhibitory nucleic acid which targets a region of a ribonucleic acid (RNA) which encodes said polypeptide. Also provided is a pharmaceutical composition comprising an inhibitory nucleic acid which targets a region of an RNA which encodes a target polypeptide expressed in a plurality of cells of a mammal, such that translation of an aberrant form of the target polypeptide occurs in said cells, said truncated form of the target polypeptide comprising one or more T cell epitopes; together with a pharmaceutically acceptable carrier or diluent.