Abstract 198: The IL-33/ST2 signaling reshapes the immune landscape and promotes leukemia transformation in acute myeloid leukemia.

Abstract Acute myeloid leukemia (AML) is an aggressive malignancy with a 5-year survival rate of ∼30%, largely due to relapse and immune evasion. Using a state-transition modeling framework on time-series RNA-seq from a Cbfb::MYH11 (CM) knock-in AML mouse model, we identified IL1RL1 (ST2), the receptor for IL-33, as a leukemia-promoting gene upregulated early in leukemogenesis. Similarly, ST2 expression is elevated in AML patients —particularly in inv(16) and t(8;21) subtypes— and correlates with poor prognosis (TCGA, n = 139, p < 0.001). ST2 regulates inflammatory responses, including Th2 immune response and mast cell activation. The ST2+ regulatory T cells (Treg) have been shown to exert immune suppression function in AML, whereas ST2's impact on the other immune cells and the molecular mechanisms remain largely unexplored. We first generated CM mice with ST2 knockout (CM-ST2-KO), which showed delayed leukemia onset, reduced circulating blasts, and extended survival compared to CM mice (median survival 192 days vs. 103 days; p < 0.0001). The scRNA-seq of leukemic stage bone marrow from CM mice revealed high ST2 expression in leukemia-enriched cell types (stem cells, erythrocytes, and mast cells). Further cell-cell communication analysis via CellChat discovered enhanced crosstalk between leukemic cells and immune cells in CM mice, which was reduced in CM-ST2-KO mice. Dysregulation of immunosuppressive pathways were identified, including PD-L1 and ALOX5, both elevated in CM and reversed in CM-ST2-KO mice. Experimental validation by ectopically overexpressing ST2 enhanced PD-L1 and ALOX5 expression, upon IL-33 stimulation. By flow cytometry, enhanced PD-L1 level was found in hematopoietic stem and progenitor cells (HSPCs) and myeloid populations, which were skewed toward immunosuppressive subsets [i.e, M2 macrophages, PD-L1high Ly6C+ myeloid-derived suppressor cells (MDSCs)] with reduced PD-L1low Ly6G+ MDSCs in CM mice. Moreover, increased expression of T cell checkpoint markers was shown, including PD-1 and TIGIT on CD8+ T cells and CD160 on CD4+ T cells. These immunosuppressive phenotypes were all reversed in CM-ST2-KO mice. Furthermore, direct co-culturing T cells from healthy mice with the Lin-cKit+ cells (LK cells) from CM mice suppressed T cell proliferation compared to LK cells from WT, which can be rescued in CM-ST2-KO co-culture. In summary, we identified ST2 as a key regulator of leukemia progression and immune suppression in AML. Our data indicates that ST2 promotes leukemic transformation and reshapes the bone marrow immune landscape by upregulating ALOX5 and PD-L1, expanding immunosuppressive myeloid populations, and enhancing T cell exhaustion. Genetic knockout of ST2 reverses these immunosuppressive phenotypes and prolongs survival, supporting the therapeutic potential of targeting ST2 to improve immune-based therapies in AML. Citation Format: Yu-Hsuan Fu, Man Li, Ying-Chieh Chen, Lianjun Zhang, Wancheng Guo, David E. Frankhouser, Denis O'Meally, Jihyun Irizarry, Jennifer Rangel Ambriz, Ziang Chen, Bin Zhang, Sergio Branciamore, Guido Marcucci, Russell Rockne, Ya-Huei Kuo. The IL-33/ST2 signaling reshapes the immune landscape and promotes leukemia transformation in acute myeloid leukemia [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2026; Part 1 (Regular Abstracts); 2026 Apr 17-22; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2026;86(7 Suppl):Abstract nr 198.