Galectin‐9 alleviates acute graft‐versus‐host disease after haplo‐hematopoietic stem cell transplantation by regulating regulatory T cell/effector T cell imbalance

Abstract Background Acute graft‐versus‐host disease (aGVHD) arises from the imbalance of host T cells. Galectin‐9 negatively regulates CD4 effector T cell (Th1 and Th17) function by binding to Tim‐3. However, the relationship between Galectin‐9/Tim‐3 and CD4 + T subsets in patients with aGVHD after Haplo‐HSCT (haploidentical peripheral blood hematopoietic stem cell transplantation) has not been fully elucidated. Here, we investigated the role of Galectin‐9 and CD4 + T subsets in aGVHD after haplo‐HSCT. Methods Forty‐two patients underwent Haplo‐HSCT (26 without aGVHD and 16 with aGVHD), and 20 healthy controls were included. The concentrations of Galectin‐9, interferon‐gamma (IFN‐γ), interleukin (IL)‐4, transforming growth factor (TGF)‐β, and IL‐17 in the serum and culture supernatant were measured using enzyme‐linked immunosorbent assay or cytometric bead array. The expression levels of Galectin‐9, PI3K, p‐PI3K, and p‐mTOR protein were detected by western blot analysis. Flow cytometry was used to analyze the proportions of CD4 + T cell subsets. Bioinformatics analysis was performed. Results In patients with aGVHD, regulatory T (Treg) cells and Galectin‐9 decreased, and the Th1, Th17, and Treg cells were significantly imbalanced. Moreover, Treg and Galectin‐9 were rapidly reconstituted in the early stage of patients without aGVHD after Haplo‐HSCT, but Th17 cells were reconstituted slowly. Furthermore, Tim‐3 upregulation on Th17 and Th1 cells was associated with excessive activation of the PI3K/AKT pathway in patients with aGVHD. Specifically, in vitro treatment with Galectin‐9 reduced IFN‐γ and IL‐17 production while augmenting TGF‐β secretion. Bioinformatics analysis suggested the potential involvement of the PI3K/AKT/mTOR pathway in aGVHD. Mechanistically, exogenous Galectin‐9 was found to mitigate aGVHD by restoring the Treg/Teffs (effector T cells) balance and suppressing PI3K. Conclusion Galectin‐9 may ameliorate aGVHD after haplo‐HSCT by modulating Treg/Teffs balance and regulating the PI3K/AKT/mTOR pathway. Targeting Galectin‐9 may hold potential value for the treatment of aGVHD.