Abstract
BACKGROUND: High-grade serous ovarian carcinoma (HGSOC) is among the most lethal gynecological malignancies, characterized by late-stage diagnosis, extensive peritoneal dissemination, and limited treatment options, resulting in poor survival outcomes. The tumor microenvironment plays a critical role in disease progression and therapy resistance, with CD4+ T cells exhibiting significant plasticity and functional heterogeneity. Regulatory T cells (Tregs) are particularly implicated in immune suppression and tumor evasion. However, the spatial distribution, functional states, and prognostic significance of CD4+ T cell subtypes in HGSOC remain poorly understood. AIM: To characterize the functional heterogeneity and tissue-specific distributions of CD4+ T cell subtypes in HGSOC and identify biomarkers for therapy. METHODS: We analyzed single-cell RNA sequencing (scRNA-seq) data from 42 HGSOC patients, examining samples collected from adnexal tissues and ascites. CD4+ T cells were identified and classified into subtypes using unsupervised clustering and marker gene analysis. Functional profiling was performed using pathway enrichment, differential expression analysis, and functional signature scoring. Kaplan-Meier survival and Cox proportional hazards modeling were conducted to evaluate the prognostic value of CD4+ T cell subtypes. RESULTS: Distinct distributions of CD4+ T cell subtypes were identified between adnexal tissues and ascites. Naive CD4+ T cells were predominant in ascites, while Tregs and CXCL13-expressing CD4+ T cells were enriched in adnexal tissues. Tregs were further categorized into four subtypes (Treg1, Treg2, Treg3, and TISG), each exhibiting unique molecular signatures and tissue-specific adaptations. Treg3 cells, enriched in adnexal tissues, were characterized by high levels of activation and exhaustion markers, correlating with poor clinical outcomes in HGSOC patients. CONCLUSION: Treg3 cells drive immune suppression and tumor progression in HGSOC, making them a key immunotherapy target. Their adnexal enrichment highlights the need for tissue-specific immune profiling in precision treatment.