Abstract A086: EMT produces an immunosuppressive tumor microenvironment
Authors: Chen Limo , Lou Yanyan , Wistuba Ignacio , Ullrich Stephen , Qin Xiao-Feng , Byers Lauren , Heymach John , Gibbons Don 
Published: November 2016

Abstract
Although recent advances in targeting immune checkpoints, such as PD-L1, PD-1, and CTLA-4, are producing durable long-term control of cancer, only a fraction of patients respond to these interventions. The identification of biomarkers that predict clinical benefit to immune checkpoint blockade is critical to successful clinical translation of these agents. Epithelial-mesenchymal transition (EMT) plays an important role in driving tumor metastasis and intra-tumoral immunosuppression, being predictive for high risk of cancer recurrence and poor survival prognosis in many major categories of cancers. We previously developed a robust EMT gene signature, highlighting differential patterns for epithelial and mesenchymal tumor cells.
To test whether EMT can be used as a potential biomarker for selecting patients more likely to benefit from immune checkpoint blockade agents, we conducted an integrated analysis of gene expression profiling from three independent large datasets (TCGA, MD Anderson's PROSPECT and BATTLE datasets) of lung adenocarcinoma patients. Comprehensive analysis of mRNA gene expression, reverse phase protein array, immunohistochemistry, and correlation with clinical data were performed. Our study demonstrates that EMT is highly associated with an immunosuppressive, inflammatory tumor microenvironment in lung adenocarcinoma, independent of tumor mutational burden. We found immune activation co-existent with elevation of immune checkpoints such as PD-L1, PD-L2, PD-1, TIM-3, BTLA, CTLA-4 and B7-H3, along with increases in tumor-infiltrating Foxp3+ regulatory T cells and immunosuppressive cytokines such as IL-6, CCL2, CXCL12, and CCL18 in lung adenocarcinomas that displayed the mesenchymal phenotype. Furthermore, we have used an immune competent syngeneic mouse model of lung adenocarcinoma with mutant Kras and p53 to perform tumor immune cell profiling and functional analyses. The data demonstrates that the ZEB1-mediated EMT represses microRNA-200 expression and de-represses PD-L1 on tumor cells, leading to immunosuppression and metastasis by CD8+ T cell dysfunction. Additionally, EMT produces marked accumulation of Foxp3+ regulatory T cells and myeloid-derived suppressor cells in mesenchymal tumors compared with epithelial tumors. More importantly, when the tumor-bearing mice were treated with anti-PD-L1 antibody alone or in combination with anti-CTLA-4 antibody, the mesenchymal tumors demonstrated greater sensitivity to the immunotherapy.
Both human and animal data demonstrate that EMT is highly associated with distinct tumor microenvironment changes, including elevation of multiple targetable immune checkpoints that are regulated at least in part by the microRNA-200/ZEB1 axis. These findings warrant further investigation of the mechanisms by which EMT regulates the immune microenvironment and using EMT as a potential predictive biomarker to guide selection of patients who are likely to benefit from immune checkpoint blockade agents in non-small cell lung cancer.
Citation Format: Limo Chen, Yanyan Lou, Ignacio Wistuba, Stephen Ullrich, Xiao-Feng Qin, Lauren Byers, John Heymach, Don Gibbons. EMT produces an immunosuppressive tumor microenvironment [abstract]. In: Proceedings of the Second CRI-CIMT-EATI-AACR International Cancer Immunotherapy Conference: Translating Science into Survival; 2016 Sept 25-28; New York, NY. Philadelphia (PA): AACR; Cancer Immunol Res 2016;4(11 Suppl):Abstract nr A086.