FOXP3+ regulatory T Cell perturbation mediated by the IFNγ-STAT1-IFITM3 feedback loop is essential for anti-tumor immunity

Targeting tumor-infiltrating Treg cells is an efficient way to evoke an anti-tumor immune response. How Treg cells fragility and stability are regulated remains largely unknown. IFITM3 and STAT1 are interferon-induced genes that play a positive role in the progression of tumors. Here, we showed that IFITM3-deficient Tregs blunted tumor growth by strengthening the tumor-killing response and displayed the Th1-like Treg phenotype with higher secretion of IFNγ. Mechanistically, depletion of IFITM3 enhances the translation and phosphorylation of STAT1. Conversely, the decreased IFITM3 protein and mRNA levels present in STAT1-deficient Treg cells indicate that STAT1 conversely regulates the expression of IFITM3 to form a feedback loop. Blocking the inflammatory cytokine IFNγ or directly depleting STAT1-IFITM3 axis phenocopies the restored suppressive function of TI-Tregs in the tumor model. Overall, our study demonstrates that the perturbation of TI-Tregs through IFNγ-IFITM3-STAT1 feedback is essential for anti-tumor immunity and constitutes a targetable vulnerability of cancer immunotherapy. To investigate the role of Ifitm3 in regulating tumor-infiltrating Treg cells of MC38 mice tumor model, we isolated tumor-infiltrating WT and IFITM3-deficient Treg cells for for RNA extraction and mRNA sequencing. Each sample includes tumor-infiltrating Treg cells from 7 tumor bearing mice.