TGF-beta promotes human T follicular helper cell stemness properties at the expense of effector function

Follicular helper T (T_FH) cells are essential for germinal center reactions and the maintenance of long-lived humoral immunity. Transforming growth factor-β (TGF-β) is a multifunctional cytokine implicated in immune regulation, T-cell differentiation, and the maintenance of cellular stemness. Prior studies have shown that TGF-β promotes stemness across a wide range of cell types and facilitates the differentiation of naïve CD4⁺ T cells into various T helper cell subsets. However, its precise effects on T_FH effector function and stem-like properties remain poorly understood.

The dual regulatory roles of TGF-β1 in modulating T_FH effector functions and stem-like properties were investigated using flow cytometry-based phenotyping, co-culture assays with memory B cells, proliferation and apoptosis assays, ELISA for antibody production, and bulk RNA sequencing of naïve-derived and blood-derived T_FH cells.

We found that TGF-β1 treatment in vitro promoted human naïve CD4⁺ T cells differentiation into CXCR3⁺ TFH, but significantly attenuated their effector molecule expression and T_FH-mediated memory B-cell differentiation and antibody production, whereas it enhanced the expression of stemness-associated molecules in T_FH cells both differentiated in vitro from naïve CD4⁺ T cells and isolated from blood. Notably, TGF-β1 promoted proliferation and reduced apoptosis of naïve-derived T_FH cells in vitro, but suppressed proliferation and increased early apoptosis in blood-derived mature T_FH cells.

Our findings indicate that TGF-β1 tunes the balance between T_FH effector function and stem-like properties, and show differential regulations of the early phase of T_FH differentiation and mature T_FH cells, which may have implications for T_FH-driven immune pathology and disease.