The lack of epithelial interleukin-7 and BAFF/BLyS gene expression in prostate cancer as a possible mechanism of tumor escape from immunosurveillance.

Abstract

The human prostate is endowed with intraepithelial and stromal lymphocytes, which may develop lymphoid follicles (LF) and allow a local immune response. We sought to investigate whether interleukin (IL)-7 and BAFF/BLyS, two fundamental survival factors for T and B cells, are expressed in the normal and neoplastic prostate and affect intraprostatic lymphocyte homeostasis. We have used real-time reverse transcription-PCR of microdissected prostatic glands and confocal microscopy to detect cytokine production, combined with immunohistochemistry to characterize intraprostatic lymphocytes. Prostatic epithelia constitutively produce IL-7 and, to a lesser extent, BAFF/BLyS. Indeed, we show that IL-7 receptor alpha is expressed by intraepithelial T lymphocytes and parafollicular T cells, whereas BAFF-R is found on periglandular B lymphocytes and mantle zone B cells of LFs. Prostate-homing B and T lymphocytes are scarcely proliferating, whereas most of them express the antiapoptotic protein bcl-2 and reveal a low apoptotic index in the terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling assay. The transition from normal to neoplastic glands in prostate cancer (PCa) is marked by a dramatic decline of IL-7 and BAFF/BLyS production. Accordingly, PCa is characterized by a significant reduction of intraepithelial lymphocytes and loss of LFs. B-cell and T-cell expression of bcl-2 decrease, whereas the apoptotic events increase. The remaining PCa-infiltrating lymphocytes are mostly CD8(+) T cells that lack terminal differentiation and barely penetrate neoplastic glands. These results suggest that epithelial IL-7 and BAFF/BLyS production support intraprostatic lymphocyte survival. Its loss in PCa is associated with a severe depletion of prostate-associated lymphocytes and points to a novel tumor escape mechanism.