Abstract A156: PDA tumor cell death as following combination anti-PD-1 blockade and CXCR4 blockade is a direct effect of CD8+ T-cells
Authors: Sullivan Kevin M. , Seo Yongwoo David , Jiang Xiuyun , Kim Teresa David , Yeung Raymond S.W. , Pillarisetty Venu G. 
Published: February 2019

Abstract
Introduction: Pancreatic ductal adenocarcinoma (PDA) is the fourth most common cause of cancer death in the United States. Despite the fact that the human PDA microenvironment contains a mixture of infiltrating immune cells, including activated effector CD8+ T-cells, attempts to apply immune checkpoint inhibitor therapy have not yet been successful in achieving a clinical response (1). Combining blockade of the immune checkpoint receptor PD-1 with blockade of the chemokine receptor CXCR4 in a mouse model of PDA produced T-cell-mediated tumor cell killing (2). We therefore hypothesized that, in a human PDA slice culture model system that maintains the intact tumor microenvironment (3), combination of CXCR4 blockade with PD-1 blockade would lead to anti-tumor T-cell activation. Methods: Cores (6 mm) were taken from freshly resected, sterile human PDA specimens and cut into 250 µm thick slices using a vibratome. The slices were treated with either IgG antibody isotype control, AMD3100 (a CXCR4 blocking small molecule drug) plus antibody isotype control, anti-PD-1 antibody, or a combination of anti-PD-1 antibody and AMD3100 for two days. The slices were then stained with fluorescently labelled antibodies for CD8 and EpCAM, as well as with SR-FLICA, a reagent that produces a fluorescent signal when bound to activated Caspase 3 and 7 enzymes. Live slices were maintained in a humidified, temperature-controlled CO2 chamber for time-lapse confocal imaging for 1 hour. Similarly, untreated slices were imaged for 90 minutes prior to and following combined anti-PD-1 and AMD3100 drug treatment. Each slice was imaged at 3 different positions to observe CD8+ T-cells, EpCAM+ tumor cells, and SR-FLICA+ apoptotic cells throughout the slice. Each cell type was counted at each position over the entire time course imaged. Results: Compared to antibody isotype control or monotherapy, slices treated with combined PD-1 and CXCR4 blockade contained a greater fraction of EpCAM+ tumor cells that were undergoing apoptosis, indicated by SR-FLICA positivity. This treatment also increased the proportion of EpCAM+ tumor cells with a CD8+ T-cell within 20 µm, and EpCAM+ cells had increased evidence of apoptosis when a CD8+ cell was nearby. When individual slices were imaged before and after combined PD-1 and CXCR4 blockade, a greater proportion of EpCAM+ cells were found to have a CD8+ cell nearby after treatment compared to before treatment, and the tumor cells with a CD8+ cell nearby were more like to be undergoing apoptosis compared to before treatment. Conclusion: Direct visualization of live pancreatic cancer slice cultures demonstrates that combined PD-1 and CXCR4 blockade enhances both the migration of CD8+ T-cells towards epithelial tumor cells and their anti-tumor cytotoxic activity. References: 1. Shibuya KC, Goel VK, Xiong W, Sham JG, Pollack SM, Leahy AM, et al. Pancreatic ductal adenocarcinoma contains an effector and regulatory immune cell infiltrate that is altered by multimodal neoadjuvant treatment. PLoS One 2014;9(5):e96565. 2. Feig C, Jones JO, Kraman M, Wells RJ, Deonarine A, Chan DS, et al. Targeting CXCL12 from FAP-expressing carcinoma-associated fibroblasts synergizes with anti-PD-L1 immunotherapy in pancreatic cancer. Proc Natl Acad Sci U S A 2013;110(50):20212-7. 3. Jiang X, Seo YD, Chang JH, Coveler A, Nigjeh EN, Pan S, et al. Long-lived pancreatic ductal adenocarcinoma slice cultures enable precise study of the immune microenvironment. Oncoimmunology 2017;6(7).
Citation Format: Kevin M. Sullivan, Yongwoo David Seo, Xiuyun Jiang, Teresa David Kim, Raymond S.W. Yeung, Venu G. Pillarisetty. PDA tumor cell death as following combination anti-PD-1 blockade and CXCR4 blockade is a direct effect of CD8+ T-cells [abstract]. In: Proceedings of the Fourth CRI-CIMT-EATI-AACR International Cancer Immunotherapy Conference: Translating Science into Survival; Sept 30-Oct 3, 2018; New York, NY. Philadelphia (PA): AACR; Cancer Immunol Res 2019;7(2 Suppl):Abstract nr A156.