Targeting EZH2 reprograms intratumoral regulatory T cells to enhance cancer immunity

Regulatory T cells (Tregs) are critical for maintaining immune homeostasis, but their presence in tumor tissues impairs anti-tumor immunity and portends poor prognoses in cancer patients. Here we reveal a mechanism to selectively target and reprogram the function of tumor-infiltrating Tregs (TI-Tregs) by exploiting their dependency for the histone H3K27 methyltransferase Enhancer of Zeste Homolog 2 (EZH2) in tumors. Disruption of EZH2 activity in Tregs, either pharmacologically or genetically, drove the acquisition of pro-inflammatory functions in TI-Tregs, remodeling the tumor microenvironment and enhancing the recruitment and function of CD8+ and CD4+ effector T cells that eliminate tumors. Moreover, abolishing EZH2 function in Tregs was mechanistically distinct from, more potent than, and less toxic than a generalized Treg depletion approach. This study reveals a novel strategy to target Tregs in cancer that mitigates autoimmunity by reprogramming their function in tumors to enhance anti-cancer immunity. Comparison of transcriptomes by RNAseq of Ezh2-deficient Tregs (4 biological replicates) versus WT Tregs (5 biological replicates) 4 days after activation in vitro with anti-CD3/anti-CD28-coated beads in the presence of IL2.