Single-cell RNA sequencing analysis to identify immune evasion in different histotypes of Ovarian Cancer

Ovarian cancer is one of the most fatal gynecological malignancies with epithelial ovarian cancer (EOC) accounting for 90% of cases. EOC comprises five major histotypes: high-grade serous (HGS), endometrioid, mucinous, and clear cell carcinoma, each with distinct molecular profiles and clinical behaviors. EOCs frequently recur, metastasize, and resist treatment. Early stages are often asymptomatic, with symptoms appearing in advance stages. The tumor microenvironment (TME) plays a crucial role in tumor progression and therapies resistance by promoting immunosuppression. In advanced stages, high levels of immunosuppressive cells create a hostile microenvironment that limits immune responses. While immune responses in advanced ovarian cancer are well studied, the TME in early-stage EOC remains poorly understood, particularly regarding transcriptional profiles, and cellular composition across histotypes. This study aims to investigate, at single-cell resolution, the TME of early-stage EOC histotypes. We performed a scRNA-seq on 5 stage-I EOC tumors isolated from patients who had total ovarian resection. CD45+ immune cells and CD45− tumor/nonimmune were FACS-sorted and analyzed via Chromium (10× Genomics), along with PBMCs from each patient. To investigate the main features, we employed computational techniques for integration, clustering strategies (Scanpy), differential gene expression analysis (Seurat). Our data revealed significant TME heterogeneity across histotypes, with a prevalence of lymphoid cells in HGS and endometrioid histotypes, while mucinous and clear cell histotypes exhibited a predominance of myeloid cells. CD4+ T cells were abundant in HGS and endometrioid histotypes, with a high prevalence of helper T cells and Tregs. Notably in HGS, Tregs account for 30–40% of CD4+ T cells, exhibiting functional heterogeneity. This study highlights the heterogeneity of the TME in early-stage EOC, and the central role of CD4+ Treg cells in immunosuppressive dynamics. The presence of Tregs in early disease stages suggest they may be a potential therapeutic target to prevent tumor progression.