TDRD3, a Tudor Domain-Containing Protein, Regulates Klf2-Dependent Treg differentiation and function to Modulate Immune Tolerance

Tudor domain-containing protein 3 (TDRD3) functions as a methylarginine reader that relays post-translational arginine methylation signals to the transcriptional machinery, thereby regulating cellular functions through modulation of gene expression. Regulatory T cells (Tregs) are pivotal for establishing and maintaining immune tolerance. In this study, we demonstrate that while TDRD3 is dispensable for thymic Tregs, it is essential for the differentiation of induced Tregs (iTregs) from naïve CD4⁺ T cells and for their immunosuppressive function. Mice with Treg-specific deletion of TDRD3 (Tdrd3fl/fl/Foxp3YFP-Cre) exhibit severely impaired iTreg, but not thymic Treg, differentiation and develop exacerbated experimental autoimmune encephalomyelitis (EAE), correlating with reduced Treg populations. Moreover, iTregs, but not thymic Tregs, derived from these mice fail to suppress colitis in adoptive transfer models, indicating compromised inhibitory capacity. Aged TDRD3-deficient mice also show spontaneous autoinflammation, characterized by splenomegaly and inflammatory infiltration in the lungs and liver, accompanied by increased IFN-γ–producing CD4⁺ T cells. Mechanistically, TDRD3 is recruited by the transcription factor FOXO1, presumably in a methylation-dependent manner, to activate Klf2 expression, which is essential for Treg differentiation. Notably, the enforced expression of Klf2 in TDRD3-deficient CD4⁺ T cells rescue both iTreg development and suppressive function. Collectively, our findings identify TDRD3 as a central transcriptional regulator of iTreg differentiation and immune homeostasis, highlighting it as a potential therapeutic target for modulating immune tolerance.