Phenotypic Analysis of Prostate-Infiltrating Lymphocytes Reveals TH17 and Treg Skewing

Abstract

Purpose: Pathologic examination of prostate glands removed from patients with prostate cancer commonly reveals infiltrating CD4⁺ and CD8⁺ T cells. Little is known about the phenotype of these cells, despite accumulating evidence suggesting a potential role for chronic inflammation in the etiology of prostate cancer. Experimental Design: We developed a technique that samples the majority of the peripheral prostate through serial needle aspirates. CD4⁺ prostate-infiltrating lymphocytes (PIL) were isolated using magnetic beads and analyzed for subset skewing using both flow cytometry and quantitative reverse transcription-PCR. The transcriptional profile of fluorescence-activated cell sorted prostate-infiltrating regulatory T cells (CD4⁺, CD25⁺, GITR⁺) was compared with naïve, peripheral blood T cells using microarray analysis. Results: CD4⁺ PIL showed a paucity of T_H2 (interleukin-4–secreting) cells, a surprising finding given the generally accepted association of these cells with chronic, smoldering inflammation. Instead, CD4⁺ PIL seemed to be skewed towards a regulatory T_reg phenotype (FoxP3⁺) as well as towards the T_H17 phenotype (interleukin-17⁺). We also found that a preponderance of T_H17-mediated inflammation was associated with a lower pathologic Gleason score. These protein level data were reflected at the message level, as analyzed by quantitative reverse transcription-PCR. Microarray analysis of pooled prostate-infiltrating T_reg revealed expected T_reg-associated transcripts (FoxP3, CTLA-4, GITR, LAG-3) as well as a number of unique cell surface markers that may serve as additional T_reg markers. Conclusion: Taken together, these data suggest that T_H17 and/or T_reg CD4⁺ T cells (rather than T_H2 T cells) may be involved in the development or progression of prostate cancer.