TIM-3 Promotes Proliferation of Acute Myeloid Leukemia Blasts

Background: The immunocheckpoint TIM-3 is also expressed on acute myeloid leukemia (AML) blasts. Its prognostic significance requires clarification through subgroup analysis, while its functional roles and underlying mechanisms remain to be further investigated. Methods: Expression of TIM-3 was assessed in fresh bone marrow samples from 81 newly diagnosed patients with AML and 7 healthy donors using multi-color flow cytometry. TIM-3 overexpression was induced in Kasumi-1 and HL60 cell lines via lentiviral infection, and subsequent assays for cell proliferation, cell cycle, apoptosis, subcutaneous tumor formation, and Western blotting were performed. Sorted CD34⁺ cells from bone marrow mononuclear cells of 4 newly diagnosed AML patients were used for evaluating Ki67⁺ frequency with TIM-3 blocked or not. CD34⁺ cells from bone marrow mononuclear cells of other 4 newly diagnosed patients with AML were sorted into TIM-3⁺ and TIM-3^- cells and subjected to transcriptome sequencing. Results: High frequencies of CD34⁺TIM-3⁺ cells at diagnosis were related to high relapse rates in AML patients with t(8;21) (p = 0.025) but not in non-CBF-AML patients (p = 0.16). In vitro, TIM-3 upregulation in Kasumi-1 and HL60 cells enhanced cell proliferation (p = 0.002 and 0.013) and increased the S phase cell population (p = 0.006 and < 0.001), without affecting apoptosis (all p > 0.05). In vivo, TIM-3 upregulation promoted subcutaneous tumor formation in BALB/c nude mice, particularly in t(8;21) AML cells (p = 0.0068 and 0.045). In addition, blocking TIM-3 tended to decrease Ki-67⁺ frequency in CD34⁺ cells of AML patients (p = 0.058). KEGG enrichment analysis of transcriptome data revealed significant enrichment of cell cycle, with key genes including CDK1, CCNA2, CDCA5, AURKB, SGO1, TTK, TICRR, and NDC80 showing significantly higher expression in CD34⁺TIM-3⁺ cells compared to CD34⁺TIM-3^- cells. Notably, CDK1 and CCNA2, critical regulators of the cell cycle, were upregulated in TIM-3-overexpressing Kasumi-1 and HL60 cells. Conclusions: High TIM-3 expression in AML blasts at diagnosis is associated with relapse in the t(8;21) subtype. TIM-3 promotes AML blast proliferation by upregulating CDK1 and CCNA2, facilitating cell cycle entry.