Enhancing adoptive T cell therapy by disrupting the SKI-SMAD2/3 axis to counteract TGF-β-mediated immunosuppression.

Transforming growth factor β (TGF-β) blockade broadly enhances antitumor immunity, while the in vivo mechanisms suppressing T cell-mediated tumor clearance remain elusive. Here, we uncover that TGF-β promotes T cell dysfunction by inducing degradation of the transcriptional co-repressor SKI, abolishing intrinsic repression of TGF-β signaling pathways. Notably, restoring SKI expression in chimeric antigen receptor (CAR)-T cells confers resistance to TGF-β-mediated immunosuppression. Proteomic analyses revealed that TGF-β stimulation triggers interaction between SMAD2/3 and SKI, leading to subsequent proteasomal degradation of SKI. Critically, engineering T cells to express SMAD2/3-binding-deficient SKI mutants (SKImut2/3) disrupts this interaction, preventing SKI degradation and significantly suppressing TGF-β signaling. Repeated tumor antigen stimulation assays under TGF-β pressure demonstrated that CAR-T cells transduced with SKImut2/3 exhibited heightened activation, increased cytokine production, and superior persistent cancer cell killing compared to unmodified cells or SKI-transduced cells in the presence of TGF-β1. Furthermore, transduction of SKImut2/3 in preclinical models of both T cell receptor and CAR-T cell therapies prolonged survival in mice bearing xenografted liquid or solid tumors. Collectively, these findings establish SKImut2/3 expression as a promising therapeutic strategy to enhance both the durability and effector function of T cell-based cancer immunotherapies.