Abstract 6044: T cell-mediated clearance of BCRABL+ leukemia cells in transgenic mice model of chronic myeloid leukemia

Abstract The BCR-ABL1 fusion gene, which is present in ∼95% of chronic myeloid leukemia (CML) patients, encodes a unique amino acid sequence that is exclusively expressed in leukemic cells. Tyrosine kinase inhibitors (TKIs) therapy targeting BCR-ABL1 are widely used as the first-line treatment for CML and has markedly improved the outcome of patients. However, there are still challenges in CML patient management, including the poor prognosis of patients with advanced-phase CML, the adverse effects associated with lifelong dependence on TKIs, and high relapse rates observed after TKI discontinuation. Restored anti-tumor immunity by immune effector cells, especially the NK cells, has been shown to be associated with deep molecular response and treatment-free remission in CML patients. However, there is a lack of direct evidence whether these cytotoxic T lymphocytes (CTLs) can really eradicate the BCR-ABL1+ leukemic cells and provide a cure for this disease. Primary murine CML was induced by the withdrawal of tetracycline (TET) from the drinking water of the SCL:tTA/BCR-ABL1 transgenic mice, which served as the donor of BCR-ABL1+ leukemia cells for serial transplantation. We performed several engraftment experiments on mice from different strains and subjected them to different treatments. The CML progression in mice engraftment model was measured by white blood cell counts (WBC) and flow cytometry analysis of peripheral blood (PB). Our findings demonstrated that non-irradiated immunocompetent C57BL/6 mice did not develop CML after transplantation of primary leukemia cells, whereas irradiated recipient mice exhibited a typical phenotype of CML, as indicated by a significant increase in the percentage of neutrophil-like CML cells and WBC. Besides, the engraftment of BCRABL1+ leukemia cells to immunodeficient NSG mice led to rapid CML progression, indicating a critical role of the immune system in CML control. To test the direct involvement of CTLs, antibody-mediated CD8+ T cells depletion was performed, which restored CML progression in C57BL/6 mice. Furthermore, in vitro tumor killing assay revealed that CD8+ T cells from transplanted, CML-free mice exhibited enhanced cytotoxic activity against BCR-ABL1+ CML cells compared to neutrophil counterparts derived from naïve mice. Consistently, when T cells from tumor-challenged but CML-free mice were transferred together with CML cells into NSG mice, the recipient NSG mice got protected from CML development. Based on these findings, we concluded that CTLs play a key anti-tumor role in the prevention of CML in the mouse CML model. Further investigating these specific cytotoxic T cells and cloning their TCR sequences could provide an experimental basis for the design of TCR-T therapy targeting BCR-ABL1 neo-antigen for the cure of CML. Citation Format: Chang Liu, Fang Hui, Xuexiu Fang, Stephanie Mori, John Kenneth Cowell, Tianxiang Hu. T cell-mediated clearance of BCRABL+ leukemia cells in transgenic mice model of chronic myeloid leukemia [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 6044.