In order to develop immunotherapies for prostate cancer, many groups are exploring vaccination strategies to induce an immune response against prostate specific antigen (PSA). To determine if T-cell recognition of PSA might be a feature of a naturally occurring human disease, we have studied patients with prostatitis, a poorly understood clinical syndrome of men in which there is evidence that an immune response directed against the prostate may be occurring. We wished to determine if a T-cell response to PSA might be occurring in these patients. We generated long-term T-cell lines from peripheral blood mononuclear cells (PBMC) of one patient with granulomatous prostatitis using purified PSA as an antigen. Several CD4+ and CD8+ TcR alpha/beta+ T-cell lines were selected for PSA reactivity as measured by at least a threefold increase in IFN-gamma secretion in response to PSA presented by irradiated autologous PBMC. CD4 and CD8 T-cell lines recognized PSA in the context of HLA-DRbeta1*1501 and HLA-B*0702, respectively. The specificity and HLA restriction of the lines was confirmed using EBV-B cell lines infected with a recombinant PSA-expressing vaccinia virus and also engineered to express PSA by retroviral transfection. HLA-matched targets infected by control vector as well as HLA-mismatched PSA-expressing targets did not induce the response. The data demonstrate that PSA-specific T cells are present in the PBMC of this patient with granulomatous prostatitis, who may be manifesting naturally the type of immune response directed at the prostate that is the goal of prostate cancer immunotherapy. However, the Class I-restricted epitope has not yet been demonstrated to be expressed on the surface of prostate cancer cells. To our knowledge, this is the first demonstration of HLA-DRB1*1501- or HLA-B*0702-restricted responses to PSA and extends the number of HLA molecules accommodating the use of PSA antigen as a candidate vaccine for prostate cancer immunotherapy.