An integrated SOX4-driven transcriptional and metabolic program governs tumor-infiltrating regulatory T cells in ovarian cancer.

Regulatory T cells (Tregs) suppress antitumor immunity in ovarian cancer (OC) and are promising targets for immunotherapy. However, the heterogeneity and regulatory mechanisms of tumor-infiltrating Tregs (TI-Tregs) remain poorly defined. Here, we aim to delineate TI-Treg programs to identify potential therapeutic targets. CD4⁺CD25⁺CD127⁻ Tregs from OC, adjacent tissues, and peripheral blood were profiled by single-cell RNA sequencing and spatial transcriptomics, with regulatory networks inferred using SCENIC. Functional and mechanistic studies of SOX4 were performed using hypoxic/tumor-conditioned models, CRISPR-Cas9 perturbation, ectopic overexpression, Cut&Tag profiling, and oxidative phosphorylation (OXPHOS) inhibition. We identified nine transcriptionally distinct Treg subsets, revealing a highly activated and immunosuppressive state among TI-Tregs. These TI-Tregs exhibited strong co-expression of TNFRSF4, TNFRSF9, TNFRSF18, and CTLA4, and their increased intratumoral abundance was independently associated with poorer overall survival. SCENIC analysis identified SOX4 as the top regulon defining TI-Treg identity, with spatial transcriptomics revealing SOX4⁺ Tregs forming an immunoregulatory barrier at tumor margins. This phenotypic identity was robustly induced by the hypoxic microenvironment and TCR stimulation in a well-established murine OC model. Mechanistically, SOX4 transactivated MT1X to promote mitochondrial fitness and OXPHOS. Consistently, Cut&Tag profiling showed reduced chromatin accessibility at OXPHOS-related loci following SOX4 depletion. Furthermore, CRISPR-Cas9-mediated disruption of SOX4 reduced FOXP3 expression and other suppressive markers, whereas SOX4 overexpression enhanced FOXP3 expression in an OXPHOS-dependent manner. Notably, pharmacological inhibition of OXPHOS abolished this effect. SOX4 is a central regulator of TI-Treg suppressive function and metabolic fitness, representing a promising therapeutic target for OC.