Abstract 5558: Whole-slide multiplexed tissue imaging of prostate adenocarcinoma reveals distinct immune niches in high- versus low-grade tumors

Abstract Objectives Tumor-immune interactions are a critical determinant of tumor evolution and are increasingly targeted by novel therapeutics (e.g. immune checkpoint blockade). However, their significance in treatment-naive localized prostate cancer remains largely unknown. Here, we employ multiplexed tissue imaging on radical prostatectomy specimens across Gleason grades to create a single-cell spatial atlas of primary prostate tumors and characterize their innate and adaptive immune landscape. Methods Whole-slide radical prostatectomy (RP) specimens were obtained from 28 patients: 14 with Gleason Grade Group ≤ 3 (Low-grade; LG) and 14 with Gleason Grade Group ≥ 4 (High-grade; HG). Tumors were imaged with our cyclic immunofluorescence (CyCIF) platform using a 27-marker panel encompassing epithelial, T-cell, innate immune and stromal markers. Tumor and stromal compartments were manually annotated by a pathologist. Cell densities were compared between tumor and stromal compartments of LG and HG tumors. Results Across the 28 RP specimens, we identified and spatially resolved over 27 million individual cells. Overall, higher Gleason grade was associated with a significantly increased innate and adaptive immune reaction. CD8+ cytotoxic T-cell density was significantly higher in HG vs LG (p = 0.003) specimens, although this effect was largely due to enrichment in adjacent stroma rather than direct tumor infiltration. By contrast, FOXP3+ T-cells were significantly increased throughout the tumor and stromal compartments of HG compared with LG tumors (p = 0.001). Tertiary lymphoid structures (TLS) and CD163+ myeloid cells were also significantly enriched in HG tumors relative to LG tumors (p = 0.029 and 0.039, respectively). PD-1+ cells were specifically enriched in TLS structures in HG tumors (p < 0.001). There were no significant differences in CD11c+ and CD103+ cell densities between LG and HG tumors. Conclusions This spatially resolved single-cell atlas of localized prostate cancer reveals that high-grade tumors exhibit significant inflammation, particularly of TLSs and stromal CD8+, and are enriched in markers of T-cell anergy and myeloid-derived suppression. These findings raise the hypothesis that immunotherapy may have activity in treatment-naïve high-grade prostate cancer, despite the failure of immune checkpoint blockade in mCRPC. Citation Format: Jeremiah Wala, Jia-Ren Lin, Brian Labadie, Daniel Peiffer, Andreánne Gagne, Kiranj Chaudagar, Yu-An Chen Chen, Eliezer Van Allen, Peter Sorger, Akash Patnaik. Whole-slide multiplexed tissue imaging of prostate adenocarcinoma reveals distinct immune niches in high- versus low-grade tumors [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 5558.