Abstract 2688: Multiplex IHC detection of immune checkpoint receptors in the tumor microenvironment

Abstract As immune checkpoint blockade has been shown to partially reverse the exhausted T cell phenotype and consequently lead to a decrease in tumor burden, there is a need for an understanding of this T cell type. Using recently developed, highly validated antibodies, we have developed a fluorescent multiplex, TSA-based assay in order to examine the interaction of PD-L1 with PD-1-expressing exhausted T cells in various tumor types. Here, we construct a seven-color multiplex panel in order to simultaneously visualize cytokeratin (the tumor mask), DAPI (nuclear counterstain), CD8 (cytotoxic T cell marker), the exhausted T cell markers PD-1, Tim-3 and Lag-3, and the ligand for PD-1, PD-L1. This technique not only enabled the concurrent detection of these markers, but also provided high-resolution visualization of interactions between PD-1-expressing CD8+ T cells and PD-L1-expressing CD68+ macrophages in the tumor microenvironment. The seven-plex panel was applied to FFPE tumor microarrays (TMAs) consisting of breast, lung and ovarian tumor tissue and each core was subsequently analyzed for the distribution, co-localization, frequency and proximity of these targets in relation to one another. While we often visualized co-expression of Lag-3 and PD-1 on T cells, Tim-3 was frequently observed on PD-L1+ macrophages in several tumor types. This data provides valuable insight into the co-expression profiles of these markers in multiple tumor types and has implications for the use of combination therapies that aim to target both the innate and adaptive immune systems. Citation Format: Jennifer E. Ziello, Sarah R. Klein, Emily Alonzo, Herbert Haack. Multiplex IHC detection of immune checkpoint receptors in the tumor microenvironment [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 2688. doi:10.1158/1538-7445.AM2017-2688