Ox40 Expression In Tumor-Associated Tregs As A Potential Prognostic Biomarker And Immunotherapeutic Target In Ovarian Cancer.

e16576 Background: Treatment of ovarian cancer (OC) remains very challenging, with 80-85% of the cases still dying after relapse to standard chemotherapy, and novel treatments are urgently needed. Expansion of regulatory T cells (Tregs) is considered the major factor limiting immune responses to OC. Agonist antibodies against the co-stimulatory receptor OX40 have recently demonstrated to abrogate Treg functions and are under clinical evaluation. We thus studied whether OX40 constituted a valid target of OC-associated Tregs. Methods: Treg immunophenotypic analyses were performed by flow cytometry in ascites and OC specimens and studied in association with patients’ outcome Results: CD4+CD25+Foxp3+ Treg% and OX40 expression were measured in 50 OC cases (36, high grade serous carcinomas; 14, other histotypes). Treg% was significantly higher in ovary (47 evaluable cases) relative to ascites (39 evaluable cases) (p u003c 0.0001). Treg% in ascites and peripheral blood from OC patients or healthy donors were not sig...