Abstract 4843: TET2 oxidizes chromatin-associated regulatory RNA m5C to potentiate anti-tumor immunity

Current immunotherapies have shown limited success in treating acute myeloid leukemia (AML) due to immune evasion, which often stems from epigenetic dysregulation of immune-related pathways. TET2, a well-studied DNA 5-methylcytosine dioxygenase, is frequently mutated and recognized as a tumor suppressor in AML. While TET2 deficiency in hematopoietic stem/progenitor cells (HSPCs) has been associated with elevated inflammation, TET2 has also been reported to promote inflammatory interferon (IFN) signaling in solid tumors, enhancing tumor responses to immunotherapies. Despite these findings, the precise role of TET2 in the response of established AML to anti-tumor immunity and the underlying molecular mechanisms remain poorly understood. By use of both syngeneic and xeno-transplantation AML mouse models, including patient-derived xenotransplantation (PDX) models, as well as in vitro co-culture systems with primary AML cells and T cells, our results revealed that TET2 sensitizes AML cells to T cell-mediated immunity by promoting the transcription of IFN-stimulated genes (ISGs). Mechanistically, we employed UHPLC-QQQ-MS/MS and optimized bisulfite-mediated 5-methylcytosine (m5C) sequencing and demonstrated that chromatin-associated regulatory RNAs (carRNAs) are modified with m5C and TET2 removes m5C from target carRNAs such as LINE1, which subsequently prevents carRNA degradation mediated by SRSF2. Loss of TET2 in AML cells leads to increased m5C levels on carRNAs and decreased LINE1 abundance, which in turn suppresses ISG transcription, facilitating immune evasion. Collectively, this study clarifies the immune-promoting role of TET2 in established AML and elucidates a previously unappreciated molecular mechanism by which TET2 promotes ISG transcription through carRNA m5C oxidation and thereby facilitates immune response. Our findings underscore the therapeutic potential of targeting the TET2-carRNA m5C-ISG pathway to overcome AML immune evasion and improve immunotherapy outcomes in AML. Citation Format: Ying Qing, Dong Wu, Yangchan Li, Keren Zhou, Keith Leung, Wei Li, Le Xuan Truong Nguyen, Lei Dong, Chao Shen, Meilin Xue, Zhenhua Chen, Kitty Wang, Lillian Sau, Mike Fernandez, Zhaoxu Xu, Yuan Che, Tingting Tang, Miao Sun, Li Han, Zhicong Zhao, Meiling Chen, Mingjiang Xu, Lili Wang, Guido Marcucci, Rui Su, Xiaolan Deng, Jianjun Chen. TET2 oxidizes chromatin-associated regulatory RNA m5C to potentiate anti-tumor immunity [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 1 (Regular Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_1):Abstract nr 4843.