Immunosuppressive milieu of high-risk localized prostate cancer.

Abstract

344 Background: The immune factors that modulate the aggressiveness of localized treatment-naïve prostate cancer remain poorly understood. Methods: Fresh tumor and peripheral blood were collected at the time of radical prostatectomy in patients with localized prostate cancer. We evaluated the immune cell composition of 22 patient samples employing multi-parametric flow cytometry. Samples were grouped by histological grade into intermediate (INTPCA) and high-grade (HIGHPCA) prostate cancers based on standard NCCN criteria and immune cell abundances were quantified by mean +/- SEM. Statistical significance was assessed using the Mann-Whitney test. Results: INTPCA and HIGHPCA tumors harbored a similar increase in CD8+ T cells ( p < 0.0005 and p < 0.05, respectively) and CD11b+CD68-CD16+ myeloid-derived cells (p < 0.05) relative to the peripheral blood. Other cell types were similarly decreased in both INTPCA and HIGHPCA, including CD11b+CD68+CD14+ ( p < 0.005 and p < 0.05, respectively). By contrast, regulatory T cells were the only cell type in our analysis to be uniquely enriched in HIGHPCA rather than INTPCA ( p < 0.05). The most unique feature found in phenotypic profiling of the immune repertoire of HIGHPCA relative to INTPCA was an increase in the immune inhibitory receptor ligand, PD-L1, in the tumor associated macrophages (CD11b+CD68+CD14+) compared to the periphery (p < 0.05). Conclusions: Collectively, our findings reveal that HIGHPCA harbors a distinct immunological landscape. Although effector CD8+ T cells are preferentially expressed in the tumor, these are met with an increased proportion of regulatory T cells as well as PD-L1 expressing macrophages that contribute to the inert tumor microenvironment. These are key features of aggressive prostate cancer that may serve as potential biomarkers and therapeutic targets.