Destruction of VISTA by TRIM25 ablation in T cells potentiates cancer immunotherapy.

The limited success of current immunotherapies emphasizes the need for new targets and combination treatments. V-domain Ig suppressor of T cell activation (VISTA) is a promising immune checkpoint target in cancer immunotherapy, but its regulatory mechanism is poorly understood. Through CRISPR knockout screening and proteomic analysis, we identify tripartite motif containing 25 (TRIM25) as a positive regulator for VISTA largely through antagonizing its degradation signaling. Moreover, ERK-mediated phosphorylation of VISTA at Thr284 enhances its interaction with TRIM25, leading to VISTA stabilization. A VISTA-derived phospho-peptide competitively disrupts TRIM25-VISTA interaction, thereby reducing VISTA expression and potentiating the anti-tumor efficacy of PD-1/PD-L1 blockade. Moreover, single-cell RNA sequencing analysis shows that tumor-infiltrating cytotoxic CD8 T cells are increased in mice with T cell-specific knockout of Trim25. Of note, genetic ablation of Trim25 in T cells not only improves anti-PD-L1 immunotherapy, but also significantly ameliorates CAR T anti-tumor activity in various mouse tumor models. Collectively, this study unveils a mechanism for VISTA regulation in T cells and highlights targeting TRIM25-VISTA as a potential strategy to enhance tumor immunotherapy.