The present invention relates to novel modified CEA agonist (or antagonist) peptides, polypeptides and proteins containing a modified epitope therein, nucleic acids coding therefor, vectors comprising said nucleic acids, mixtures and compositions of the aforementioned agents, and their advantageous use in generating CEA-specific immune responses and/or in the treatment of cancers and the present invention further relates to the foregoing combined with one or more costimulatory molecules.