Abstract
BACKGROUND: Regulatory T cells (Tregs) play an important role in the antitumor immune response in epithelial ovarian cancer (EOC). To understand the immune-inhibitory networks of EOC, we addressed the association between Tregs and immune checkpoint expression on T cells in the tumor microenvironment of EOC. METHODS: A total of 41 patients with stage IIIC and IV EOC were included in the analysis. We harvested cells from malignant ascites and investigated them using multi-color flow cytometry. We categorized the Tregs into 3 groups: effector-type Tregs, naïve Tregs and non-Tregs, based on the expression patterns of CD45RA and Foxp3 in CD4(+) T cells. Furthermore, the relationships between the expression of various immune checkpoint molecules, such as PD-1, on CD8(+) T cells and each of the Treg subtypes was also evaluated. RESULTS: The median frequency of naïve Tregs, effector-type Tregs and non-Tregs were 0.2% (0-0.8), 2.0% (0-11.4) and 1.5% (0.1-6.3) in CD4(+) T cells of malignant ascites from EOC patients, respectively. A high frequency of effector-type Tregs was associated with high-grade serous carcinoma compared with the other histotypes. Patients with higher proportions of effector-type Tregs showed a trend towards increased progression-free survival. We also demonstrated a correlation between a higher proportion of effector-type Tregs and increased PD-1 expression on CD8(+) T cells. In addition, C-C chemokine receptor 4 expression was also observed in effector-type Tregs. CONCLUSION: These data suggest that multiple immune-inhibitory networks exist in malignant ascites from EOC patients, suggesting an approach towards combinational immunotherapies for advanced EOC patients.