The invention is a prostate specific antigen oligo-epitope peptide which comprises more than one PSA epitope peptide, which conforms to one or more human HLA class I motifs. The prostate specific antigen oligo-epitope peptide in combination with various HLA-class I molecules or interactions with various T-cell receptors elicits PSA specific cellular immune responses. The prostate specific antigen oligo-epitope peptide is useful as an immunogen in the prevention or treatment of prostatic cancer, in the inhibition of prostatic cancer cells and in the establishment and characterization of PSA-specific cytotoxic T-cell lines.