This invention relates to isolated peptides comprising agonist epitopes of prostate-specific antigen (PSA). In various aspects, the invention relates to peptides comprising agonist epitopes of the PSA-3 cytotoxic T lymphocyte epitope, and nucleic acids encoding peptides that comprise PSA-3 agonist epitopes. Also related are probes, primers, and vectors comprising these nucleic acids, as well as host cells comprising these vectors, and antibodies that bind to the PSA-3 agonist peptides. This invention further relates to diagnostic reagents and methods utilizing the disclosed nucleic acids or antibodies. The invention also relates to pharmaceutical compositions comprising the nucleic acids, host cells, and peptides of the invention, as well as methods of treatment or prevention of prostate cancer employing such compositions, for example, for peptide-mediated, cell-mediated, and vector-mediated immunotherapies.