TGF-β and IL-2 differentially shape T follicular regulatory cell differentiation and stability in vitro

In the GC, Tfh cells help B cells to proliferate and to differentiate into memory B cells and long-lived plasma cells. In contrast, Tfr cells, a specialized subset of regulatory T cells (Tregs), modulate the humoral immune response by suppressing excessive or autoreactive B-cell activity.

Here, we established an in vitro differentiation protocol for mouse CD4⁺ T cells that yielded CXCR5⁺FoxP3⁺ Tfr cells that exhibited a Bcl6hiPD-1hiCD25loGITRint phenotype and were distinct from Treg and Tfh cells. Functionally, in vitro-generated Tfr cells potently suppressed Tfh cell-driven B-cell class switching to IgG1 and downregulated the expression of B-cell costimulatory ligands. While in vitro-generated Bcl6-deficient Tfh cells were impaired in providing help to B cells for efficient class switching to IgG1, in vitro-generated Bcl6-deficient Tfr cells failed to inhibit Tfh cell-driven B-cell class switching to IgG1.