Activated Galectin-9/Tim3 promotes Treg and suppresses Th1 effector function in chronic lymphocytic leukemia

Tim-3 is a negative immunoregulator in anti-tumor response, but its mechanism in chronic lymphocytic leukemia (CLL) is not yet clear. The aim of this study was to understand the role of Galectin-9/Tim-3 signaling pathway in the regulation of CD4⁺ T cell subsets in CLL patients. Flow cytometry results showed that the number of Treg cells obviously increased, and there was a significant Treg/Th17 imbalance in CLL patients. In addition, Tim-3 overexpressed on the surface of Th1 and Treg cells in CLL patients. The levels of Galectin-9 and IL-10 were significantly elevated in patients of CLL, especially in stages of Binet B, and C. However, IFN-γ decreased. Moreover, Galectin-9 in CLL patients was positively correlated with the number of Tim-3⁺ Treg cells and the level of IL-10. Interestingly, when the Tim-3/Galectin-9 pathway was blocked in vitro, the level of IL-10 in the culture supernatant of CD4⁺ T was significantly reduced, while the levels of IFN-γ and TNF-α were increased. After co-culture with activated Th1 cells, the apoptosis of CLL cells was significantly increased, and this effect was reversed after treatment with Tim-3⁺ Tregs. In summary, Galectin-9/Tim-3 are elevated in CLL and associated with disease progression. By the negative regulation of CD4⁺ T cells, activated Galectin-9/Tim-3 suppresses Th1 effector function and also promotes Treg to be involved in immune escape of CLL. This pathway might become the potential target of immunotherapy in CLL patients.