Abstract. Prostate-specific antigen (PSA) is a potentially useful antigen for targeted T-cell immunotherapy of prostate cancer (CaP). Our laboratory has identified a synthetic nonamer peptide (PSA 146154) homologue of PSA, which binds to the prevalent human leukocyte antigen, HLA-A2, and elicits specific cytotoxic T-lymphocyte (CTL) responses from normal individuals of the HLA-A2 phenotype. In the present study, we report on the induction of CTL from peripheral blood mononuclear cells (PBMC) of patients with hormone-refractory CaP, which exhibit the same specificity. T-cell lines were established from two patients by stimulation of PBMC with PSA 146154 peptide in vitro. The T-cell lines exhibited specific cytolytic activity against T2 cells pulsed with PSA 146154 peptide, but not a control HLA-A2 binding peptide (HIV-RT 476484) via chromium release assay (CRA). The T-cell lines also showed PSA 146154 peptide-specific IL-4 responses, but no detectable interferon-gamma (IFN-) responses via enzyme-linked immuno-spot assays. Magnetic immuno-selection studies of one of the T-cell lines demonstrated that both cytolytic and interleukin-4 (IL-4) responses were mediated by CD8+, but not by CD4+ T cells. This Tc2 line was further characterized for the ability to recognize endogenously processed PSA epitopes. The line specifically secreted IL-4 in response to HLA-A2+ target cells transfected to express PSA and specifically lysed the PSA+ target cells, but not control transfected cells. The results indicate that the PSA 146154 peptide emulates a naturally processed and presented peptide epitope of PSA that is within the T-cell repertoire of HLA-A2+ patients with CaP.