Identification of HLA-DRB1*1501–Restricted T-cell Epitopes from Prostate-Specific Antigen

Abstract

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 Tcells 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][172][173][174][175][176][177][178][179][180][181][182][183][184][185][186][187][188][189][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.

High-throughput monitoring of human tumor-specific T-cell responses with large peptide pools

“…In contrast to CD8 C T cells, CD4 C T cells recognize epitopes presented by MHC class II molecules and libraries of longer (20-mer) overlapping peptides are generally used to screen for antigen-specific responses. 19 We thus measured the response of Melan-A/ MART-1 [25][26][27][28][29][30][31][32][33][34][35][36] -specific CD4 C T-cell clones 20 spiked into PBMCs of HLA-DQ6 C donors in the presence of 20-mers overlapping peptide pools (1 mM each). As shown in Fig.…”

Experimental rodent models of prostatitis: limitations and potential

“…10,12,13 The remaining 60-95% cases of clinical prostatitis (categories IIIA and IIIB) may involve (i) hormonal imbalance; 14,15 (ii) neurological dysfunction; 16,17 (iii) a-adrenergic system abnormalities; [18][19][20] (iv) urinary reflux into the prostate; [21][22][23] (v) inappropriate cytokine release [24][25][26][27][28][29][30][31][32] and/or (vi) an autoimmune response. [33][34][35][36][37] The patients typically have repeat episodes of prostatitis and therapy is 'hit or miss'. Quality-of-life may be significantly diminished.…”

HLA class II antigen presentation by prostate cancer cells

“…[16][17][18] While this type of therapy has shown limited success in killing prostate tumor cells, an elevated and sustainable immune response cannot be achieved without stimulation of the immune system via the HLA class II pathway. [19][20][21][22] The HLA class II molecule is an a/b heterodimer that is synthesized and assembled in the endoplasmic reticulum along with a third glycoprotein, the invariant chain (Ii). 23,24 The associated complex is transported from the endoplasmic reticulum (ER) through the trans-Golgi apparatus to endosomes for further processing.…”

“…Prostate-specific antigen, prostatic acid phosphatase and prostate-specific membrane antigen (PSMA) are arguably the best characterized prostate associated tumor antigens, [19][20][21][22] containing both class I-and class II-restricted peptides for T-cell recognition. While class I-restricted cytolytic CD8 þ T cells are the main effector cells in killing tumors, class II-restricted CD4 þ T cells play critical roles in initiating, regulating and maintaining antitumor immune responses.…”

“…While class I-restricted cytolytic CD8 þ T cells are the main effector cells in killing tumors, class II-restricted CD4 þ T cells play critical roles in initiating, regulating and maintaining antitumor immune responses. [19][20][21][22] Thus, we examined whether malignant prostate tumors express functional HLA class II molecules. We show that the majority of prostate tumors express detectable levels HLA class II proteins recognizable by CD4 þ T cells.…”