Activated regulatory and memory T-cells accumulate in malignant ascites from ovarian carcinoma patients

Invasive ovarian cancer is associated with poor outcome. The presence of infiltrating regulatory T-cells (Tregs) suppresses protective anti-tumor immune responses, and their accumulation into the tumor microenvironment correlates with reduced survival in ovarian cancer patients. Here, we conducted a detailed characterization of CD4⁺ T-cells, CD8⁺ T-cells and Treg subsets in the peripheral blood and malignant ascites fluid from seventeen patients with ovarian carcinoma of epithelial origin. Cell distribution, activation status and proliferation status were assessed by multi-color flow cytometry. In ascites fluid, a significant accumulation of CD8⁺ cytotoxic T-cells and Tregs was observed compared to peripheral blood. Furthermore, a skewing toward the CD45RA⁻ effector/memory compartment was observed in all T-cell subsets in the ascites fluid, but was most pronounced in the Treg population. Regulatory T-cells in the malignant ascites were more activated and had a higher proliferation rate compared to blood-derived cells from the same patient, and their number in ascites was positively correlated with the number of epithelial cells in effusion. In summary, we demonstrate an accumulation of activated CD4⁺, CD8⁺ and regulatory T-cells in the cancer microenvironment of ovarian carcinoma.