Abstract 6164: Tumor-intrinsic PRC2 inactivation drives a context-dependent immune-desert tumor microenvironment
Authors: Yan Juan , Chen Yuedan , Patel Amish J. , Lee Cindy J. , Warda Sarah , Nixon Briana G. , Wong Elissa W. P. , Miranda-Román Miguel A. , Yang Ning , Wang Yi , Sher Jessica , Giff Emily , Tang Fanying , Khurana Ekta , Singer Sam , Liu Yang , Galbo Phillip M. , Maag Jesper L. , Koche Richard P. , Zheng Deyou , Antonescu Cristina R. , Li Ming , Deng Liang , Chen Yu , Chi Ping 
Published: June 2022

Abstract
Immune checkpoint blockade (ICB) has demonstrated clinical success in “inflamed” tumors with significant T-cell infiltrates, but tumors with an immune-desert tumor microenvironment (TME) fail to benefit. The tumor cell-intrinsic molecular mechanisms of the immune-desert phenotype remain poorly understood. Here, we demonstrate that inactivation of the Polycomb-repressive complex 2 (PRC2) core components, EED or SUZ12, a prevalent genetic event in malignant peripheral nerve sheath tumor (MPNST) and sporadically in other cancer types, drives a context-dependent immune-desert TME. PRC2 inactivation reprograms the chromatin landscape that leads to a cell-autonomous shift from primed baseline signaling-dependent cellular responses (e.g., interferon γ) to PRC2-regulated development and cellular differentiation transcriptional programs. Further, PRC2 inactivation reprograms the TME, leads to diminished tumor immune infiltrates and immune evasion through reduced chemokine production and impaired antigen presentation and T-cell priming, and confers ICB primary resistance through blunted T-cell recruitment in vivo. We demonstrate that strategies that enhancing innate immunity via intratumoral delivery of inactivated modified vaccinia virus Ankara (MVA) leads to increased tumor immune infiltrates and sensitizes PRC2-loss tumors to ICB. Our results provide novel molecular mechanisms of context-dependent dysfunctional epigenetic reprogramming that underline the immune-desert phenotype in MPNST and other cancers with PRC2 inactivation. Importantly, our findings highlight genetic-inactivation of PRC2 as a novel context-dependent ICB therapeutic resistance biomarker in cancer, and caution that therapeutic strategies that non-selectively target PRC2 in the host may lead to undesirable context-dependent immune evasion and ICB resistance in tumors. Our studies also point to intratumoral delivery of immunogenic therapeutic viruses as an initial strategy to modulate the immune-desert TME and capitalize on the clinical benefit of ICB.
Citation Format: Juan Yan, Yuedan Chen, Amish J. Patel, Cindy J. Lee, Sarah Warda, Briana G. Nixon, Elissa W. P. Wong, Miguel A. Miranda-Román, Ning Yang, Yi Wang, Jessica Sher, Emily Giff, Fanying Tang, Ekta Khurana, Sam Singer, Yang Liu, Phillip M. Galbo, Jesper L. Maag, Richard P. Koche, Deyou Zheng, Cristina R. Antonescu, Ming Li, Liang Deng, Yu Chen, Ping Chi. Tumor-intrinsic PRC2 inactivation drives a context-dependent immune-desert tumor microenvironment [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 6164.