STAT6 inhibition stabilizes induced regulatory T cells and enhances their therapeutic potential in inflammatory bowel disease.

The development and stability of induced regulatory T cells (iTregs) are essential for their immunosuppressive function and therapeutic potential in inflammatory diseases. Although Treg-based immunotherapy offers promise for restoring immune tolerance, clinical application is limited by the instability and reduced potency of iTregs. STAT6 signaling has been implicated in destabilizing Foxp3 expression, a key marker of Treg identity. Here, we investigated the impact of pharmacological STAT6 inhibition on iTreg differentiation, stability, and function both in vitro and in vivo. Naïve CD4⁺ T cells were differentiated into iTregs under standard conditions or expanded with IL-2 in the presence of the STAT6 inhibitor AS1517499 (AS-iTregs). STAT6 inhibition enhanced iTreg stability, maintaining high expression of Foxp3, CD25, PD-1, and CTLA-4 for up to 10 days, even in inflammatory conditions. AS-iTregs also showed increased mRNA levels of Foxp3, IL-10, TGF-β, and PD-1, and reduced IL-6, IL-1β, and DNMT1 expression-suggesting improved functional and epigenetic stability. In the DSS colitis model, adoptive transfer of AS-iTregs alleviated disease severity, preserved mucosal architecture, and increased goblet cell numbers. Histopathological analysis showed reduced epithelial damage and inflammation compared to controls. Importantly, AS-iTregs did not promote tumor growth in a colitis-associated cancer model. Furthermore, in vivo administration of AS1517499 during acute colitis enhanced Treg expansion, activation, and suppressive function. These findings establish STAT6 inhibition as a promising approach to boost iTreg stability and efficacy, advancing the potential of Treg-based therapies for inflammatory disorders.