Identification of HLA-DRB1*1501-restricted T-cell epitopes from prostate-specific antigen.

The development of immunotherapy for prostate cancer based on the induction of autoimmunity to prostate tissue is very attractive because prostate is not a vital organ beyond the reproductive years. CD4 T cells play an important role in the development of antitumor immune responses, yet the identification of naturally processed MHC Class II-restricted epitopes derived from prostate differentiation antigens has not been described. To facilitate the search for prostate-specific antigen (PSA)-derived MHC class II-restricted peptides, we immunized mice transgenic for HLA-DRB1*1501 with human PSA and showed a robust dose-dependent immune response to the antigen. Screening a library of overlapping 20-mer peptides that span the entire PSA sequence identified two 20-mer peptides, PSA(171-190) and PSA(221-240), which were responsible for this reactivity. Immunization of DR2b transgenic mice with these peptides induced specific responses to the peptide and whole PSA. Identified peptides were used to stimulate CD4 T cells from HLA-DRB1*1501+ patients with a rare condition, granulomatous prostatitis, and who seem to have a preexisting immune response directed against the prostate gland. We previously showed a linkage of granulomatous prostatitis to HLA-DRB1*1501, suggesting that this disease may have an autoimmune etiology. Peptide-specific CD4 T-cell lines were generated from the peripheral blood of these patients as well as one patient with prostate cancer. These lines also recognized whole, processed PSA in the context of HLA-DRB1*1501. This study will be instrumental in understanding the interaction between circulating self-reactive T cells, organ-specific autoimmunity, and antitumor immune response. The use of these peptides for the immunotherapy of prostate cancer is under investigation.

Identification of HLA-DRB1*1501-restricted T-cell epitopes from human prostatic acid phosphatase.

BACKGROUND: The crucial role of CD4 T-cells in anti-tumor immune response is widely recognized, yet the identification of HLA class II-restricted epitopes derived from tumor antigens has lagged behind compared to class I epitopes. This is particularly true for prostate cancer. Based on the hypothesis that successful cancer immunotherapy will likely resemble autoimmunity, we searched for the CD4 T-cell epitopes derived from prostatic proteins that are restricted by human leukocyte antigen (HLA)-DRB1*1501, an allele associated with granulomatous prostatitis (GP), a disease that may have an autoimmune etiology. One of the antigens implicated in the development of autoimmunity in the prostate is prostatic acid phosphatase (PAP), which is also considered a promising target for prostate cancer immunotherapy. METHODS: We immunized transgenic (tg) mice engineered to express HLA-DRB1*1501 with human PAP. A library of overlapping 20-mer peptides spanning the entire human PAP sequence was screened in vitro for T-cell recognition by proliferative and interferon (IFN)-gamma enzyme-linked immunosorbent spot (ELISPOT) assays. RESULTS: We identified two 20-mer peptides, PAP (133-152), and PAP (173-192), that were immunogenic and naturally processed from whole PAP in HLA-DRB1*1501 tg mice. These peptides were also capable of stimulating CD4 T lymphocytes from HLA-DRB1*1501-positive patients with GP and normal donors. CONCLUSIONS: These peptides can be used for the design of a new generation of peptide-based vaccines against prostate cancer. The study can also be helpful in understanding the role of autoimmunity in the development of some forms of chronic prostatitis.

Activation of innate immunity by prostate specific antigen (PSA).

BACKGROUND: Prostate specific antigen (PSA) is a serine protease secreted by the prostatic epithelium. The only known function of the protein is to cleave seminogelin. We wished to determine if PSA activated peripheral blood mononuclear cells (PBMC). METHODS: PBMC and selected sub-populations were cultured with purified PSA. Secretion of IFNgamma was measured by cytokine capture flow cytometry and enzyme-linked immunosorbent assay. RESULTS: We observed secretion of IFNgamma and a proliferative response in PBMC cultured with PSA. We found that NK cells were the source of the IFNgamma but NK cells were not directly stimulated by PSA. Rather, a soluble factor secreted primarily by CD14 monocytes in response to PSA stimulated NK cells to secrete IFNgamma. DISCUSSION: PSA induces a pro-inflammatory response that results in the secretion of INFgamma by NK cells. The presence of large amounts of PSA could contribute to the common finding of inflammatory infiltrates in the prostate.

CD4 and CD8 T-lymphocyte recognition of prostate specific antigen in granulomatous prostatitis.

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.

Granulomatous prostatitis linked to HLA-DRB1*1501.

PURPOSE: Granulomatous prostatitis is characterized by a pattern of granulomatous inflammation in the prostate. In most cases the etiology is unknown. Based on the hypothesis that granulomatous prostatitis may be an autoimmune disease we performed intermediate and selective high resolution typing of HLA-DR in a group of patients with the disease and compared the frequency of class II HLA phenotypes to that in a control group of volunteer marrow donors in the military. MATERIALS AND METHODS: Histological records from 1 institution from 1990 to 2000 revealed 12 patients with diffuse granulomatous prostatitis. Three patients were dead and 1 refused blood drawing. Peripheral blood from the remaining 8 patients was typed along with blood from an additional 3 identified at the practice of one of us from 1999 through 2002. All slides were reviewed by 1 pathologist. Intermediate resolution typing of HLA-A, B and DR was performed by polymerase chain reaction-sequence specific oligonucleotide probe. High resolution, allele specific identification of HLA DR15 was performed if patients were DR15 positive by intermediate resolution typing. RESULTS: There were 3 black and 8 white individuals identified with diffuse nonspecific granulomatous prostatitis. Six of 8 white patients (75%) were HLA-DR15 by intermediate resolution typing. One of the 3 black American patients (33%) was HLA-DR15. In the control group 127 of 451 white (28.2%) and 23 of 89 black (25.8%) volunteer marrow donors were HLA-DR15. The case-control comparison of white patients was significantly different (Fisher's exact test p = 0.0086). There were no statistically significant differences between case-control comparisons for any other HLA-DR phenotype. High resolution DR15 typing showed that the white patients were HLA-DRB1*1501 and the black patient was HLA-DRB1*1503. CONCLUSIONS: The data suggest an association between HLA-DRB1*1501 and granulomatous prostatitis. HLA-DR15 is strongly associated with other autoimmune diseases, notably multiple sclerosis. The data are consistent with an autoimmune etiology for nonspecific granulomatous prostatitis.