LAUSR

Introduction: Many solid tumors such as prostate cancer have shown limited response to immunotherapy treatment. Whether this is due to absence of tumor specific antigens or poor immune infiltrate, the exact mechanism is not well understood. Our study evaluates the presence and spatial distribution in benign versus malignant tissue of CD4+ and CD8+ cells in whole mounted radical prostatectomies samples and characterized the subset of intraepithelial CD103+ and CD39+ cells, which have been previously shown to harbor more cancer specific T-cells. Materials and Methods: Sixteen cases of whole mounted radical prostatectomy samples were used to asses CD4, CD8, CD103 (all abcam) and CD39 (Sigma) expression by IHC. Location of positive cells within epithelium and stroma in tumor and benign prostatic tissue was evaluated. The results were confirmed using QuPath Software, for positive detection of immune cells by color deconvolution and threshold adjustments. Results: The CD4 and CD8 staining demonstrated that most of the immune cells were present in the stroma but not within the malignant glands. The whole prostate sections (mean size 51.4 × 44mm) generated around 1650 ROI9s per/case. All the ROI9s were included in the analysis. CD4+ and CD8+ were evaluated in whole gland vs tumor area. No significant difference = of CD4+ and CD8+ cell density was seen between whole prostate area and tumor areas (CD4+ 2.9 vs 1.9%) and (CD8+ 1.3 vs 1.2%). The density of CD4+ and CD8+ cells in tumors vs benign gland was approximately the same (means 0.93 for both). For the CD103+ analysis, the positive cells were rarely found in the tumor epithelium in comparison with the benign glands (mean 1.09 vs 5.41; representing 2 vs 9.3% of the total lymphocytes). The CD39 stain showed positive cells mostly at the benign epithelium. No correlation was found between our results and Gleason grade, stage or prognosis. Conclusion: Our study suggests the possibility that in solid cancers such as prostate cancer, immune cells may not be able to reach appropriately the malignant epithelium with only a small subset of T cells reaching their target. This may have important clinical implication for the success of the immune therapy in this group of patients. Further studies are being performed to deeply characterized the tumor infiltrating cell population. Citation Format: Beatriz Walter, Billel Gasmi, Xu Naizen, Vladimir Valera, Peter Pinto, Maria J. Merino. Where do the T lymphocytes go in prostate cancer: Correlation with CD103, CD39 expression and clinical pathological parameters [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 4984.