Abstract A01: Ex vivo evaluation of an anti-Müllerian hormone type II receptor humanized antibody with optimized Fc effector function in ovarian cancer

Abstract

Abstract Purpose of the study: Epithelial ovarian cancer (OC) is one of the most common gynecologic malignancies and the fifth most frequent cause of cancer death in women. Paclitaxel and Carboplatin chemotherapy (CT) remains the standard treatment, but tumor relapses in approximately 80% of patients, mostly due to drug resistance. Novel therapeutic options are therefore strongly required. Recently, human Anti-Müllerian Hormone type II Receptor (AMHRII) has been identified as a potential target, but up to date the AMHRII expression in ovarian tumors has been poorly documented. A humanized glyco-engineered monoclonal antibody (mAb) called 3C23K with higher Fc effector function has been developed. The aim of this study is to investigate the potential efficacy of this mAb by assessing AMHRII expression and analyzing the localization and amount of mAb responsive immune effectors in OC patient and in a patient-derived xenograft (PDX) model. Experimental procedures: AMHRII expression was prospectively studied in fresh biopsies (primary ovarian tumors, peritoneal carcinomatosis and ascites) from a cohort of 28 patients, by means of both flow cytometry (FC) and immunofluorescence (IF). We have characterized the intratumoral immune infiltrate by FC and determined the localization of immune cells within the tumor by IF. Similar experiments were performed on an undifferentiated highly proliferative serous ovarian adenocarcinoma PDX model, in parallel to in vivo efficacy study of 3C23K alone or in combination with standard CT. The antitumor activity of infiltrating immune cells isolated from OC patients (peritoneal washing) was assessed using red blood cells as target and a glyco-engineered anti-D Rhesus mAb. The antibody-dependent cell cytotoxicity (ADCC) and the antibody-dependent cell phagocytosis (ADCP) abilities of 3C23K against AMHRII+ cells (COV434-RII) were analyzed by IF using monocyte-derived macrophages (MDM) from blood of healthy donors as effector cells. Summary of the data: Here, we show that among the 28 ovarian tumors tested, 19 patients (68%) were positive for AMHRII with at least 15% of tumor cells being positive for AMHRII. OC are largely composed of (CD45+) immune cells mostly composed of tumor associated macrophages (TAMs) and tumor infiltrating lymphocytes (TILs). TAMs highly express M2-like markers, such as CD206, but also strongly express the Fcγ III receptor (CD16). Unlike TILs, which accumulate in the peritumoral stroma, CD16+ TAMs are found in both the stroma and the tumor islets. Moreover, tumors infiltrating immune cells are able to induce a mAb-dependent cytotoxicity ex vivo. In parallel, in vivo experiments have shown an intermediate efficacy of the 3C23K antibody administered alone and a significantly increased antitumor effect in combination with CT including a prolonged survival. IF and FC analyses showed high TAM infiltration compatible with induction of ADCP by 3C23K in this model. Furthermore, 3C23K mAb induces ADCC and/or ADCP of COV434-RII cells by MDM likely through CD16 interaction, either in the absence or presence of saturating concentrations of Ig. Conclusions: We have confirmed the expression of AMHRII in 2/3 of OC patients. MAb responsive immune effectors and particularly macrophages largely infiltrate OC and are found in contact with malignant cells. Targeting AMHRII by the 3C23K mAb dramatically increases the efficacy of a standard CT in vivo. 3C23K appears to act through macrophage-induced ADCC and/or ADCP of tumor cells and current studies are designed to refine its mechanism of action. Our results indicate that most ovarian tumors display optimal conditions for a 3C23K-based immunotherapy. Hence, the combination of 3C23K with CT could bring additional therapeutic benefit in OC patients compared to standard chemotherapy. Citation Format: Houcine Bougherara, Fariba Némati, Christophe De Romeuf, Jean-Marc Barret, Gérald Massonnet, Marie-Aude Le Frère-Belda, Jean-François Prost, Didier Decaudin, Emmanuel Donnadieu. Ex vivo evaluation of an anti-Müllerian hormone type II receptor humanized antibody with optimized Fc effector function in ovarian cancer. [abstract]. In: Proceedings of the AACR Special Conference: Tumor Immunology and Immunotherapy: A New Chapter; December 1-4, 2014; Orlando, FL. Philadelphia (PA): AACR; Cancer Immunol Res 2015;3(10 Suppl):Abstract nr A01.