Antibody and T-cell responses specific for the androgen receptor in patients with prostate cancer

The androgen receptor (AR) is a steroid hormone receptor that is an essential regulator of prostate development, and the primary molecular target for the treatment of metastatic prostate cancer. In this report, we evaluated whether patients with prostate cancer have pre-existing immune responses specific for the AR as evidence that the AR also might be pursued as an immunological target antigen.

The detection of auto-antibodies specific for the AR in patient sera was evaluated by ELISA and Western blotting. Peripheral blood mononuclear cells were analyzed for the presence of AR-specific T-cells, as measured by T-cell proliferation, interferon gamma (IFNgamma) and interleukin-10 secretion.

We found that a significantly higher frequency of prostate cancer patients have AR LBD-specific antibody responses than do healthy male volunteers [18/105 cancer patients (17.1%) vs. 0/41 healthy volunteers, P = 0.0049], and that these responses were present regardless of the patients' disease stage [8/46 organ-confined prostate cancer patients (17.4%), 3/22 metastatic androgen-dependent patients (13.6%), and 7/37 metastatic, androgen-independent patients (18.9%)]. These antibodies were pre-dominantly of the IgG isotype, and furthermore of the IgG(2) sub-isotype. In addition, we found that patients with antibody responses also had concurrent antigen-specific CD4+ and CD8+ T-cell proliferation and IFNgamma secretion when compared to patients without antibody responses.

These data demonstrate that some patients with prostate cancer have pre-existing humoral and cellular immune responses specific for the AR, suggesting that tolerance against the AR is not absolute and that the AR may be a potential immunotherapeutic target antigen.