Abstract 4749: VISTA immune checkpoint deregulation in human triple-negative breast cancer

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Abstract Immunotherapy for breast cancer has lagged behind the advances in other tumor types, suggesting the need for novel immune targets. VISTA/PD-1H is a checkpoint receptor expressed on immune cells that is an effective anti-cancer target in mouse models and now in early human clinical trials. We utilized an in vitro system to examine epigenetic changes arising early after depletion of breast cancer tumor suppressor proteins. This demonstrates that epigenetic alterations occur in normal human mammary cell lines lacking BRCA2 and result in regulation of VISTA through an NF-kB-dependent pathway. VISTA is strongly induced by growth factor limitation, an effect that is blunted by BRCA2-induced NF-kB activation and binding to a kB site in the VISTA promoter. This suggests that repression of VISTA may be an early consequence of BRCA2 depletion in pre-neoplastic tissues leading to immune infiltration. In contrast, in primary, untreated human triple-negative breast cancers, VISTA is over-expressed on tumor cells, independent of its presence on immune cells. VISTA positive TNBCs (14%) have significantly increased tumor infiltrating lymphocytes (TILs) whereas VISTA strong positive TNBCs (6%) have significantly decreased TILs and tumor PD-L1 staining, suggesting a higher level of immunosuppression. Gene expression and tumor genomics in TNBCs suggests that transcriptional networks to regulate physiologic immunoreceptor levels are corrupted during malignant transformation. In summary, this work identifies a BRCA2-loss-of-function signaling pathway that regulates an important immune checkpoint molecule via NF-kB activation in pre-neoplastic tissues and triple-negative breast cancers with important consequences for the immune microenvironment. We expect these observations to enhance immunotherapeutics for breast cancer. Citation Format: Joshua J. Gruber, Marisa M. Juntilla, Soo-Ryum Yang, Benjamin Geller, Natalie Jager, Chien-Yu Lin, Andrew M. Lipchik, Justin Chen, Ashwin Ram, Shaveta Vinayak, Melinda L. Telli, Robert B. West, James M. Ford, Michael P. Snyder. VISTA immune checkpoint deregulation in human triple-negative breast cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 4749.