Discovery And Characterization Of New Original Blocking Antibodies Targeting The Cd73 Immune Checkpoint For Cancer Immunotherapy

CD73 (NT5E) is a cell membrane ectoenzyme of the NTPDase family that plays a major role in the conversion of AMP into Adenosine (Ado). Within the tumor microenvironment, accumulation of Ado causes immune suppression and dysregulation of immune cell infiltrates resulting in tumor spreading. CD73 expression in the tumor environment has been associated with poor disease outcome and/or with a pro-metastatic phenotype. Thus, targeting CD73 may promote anti-tumor immunity by reducing Ado accumulation and may block tumor cell metastasis by inhibiting CD73 on tumor cells. Here, we describe the generation and characterization of novel anti-human CD73 antibodies, intended for the treatment of a wide range of cancers. The research leading to these results has received funding from the European Community9s Seventh Framework Program (FP7/2007-2013) under grant agreement n°602200. Antibodies were discovered that inhibited CD73 function by different mechanisms, including the direct blocking of CD73 enzymatic activity or the down-modulation of membrane CD73 expression. Epitope mapping revealed that antibodies acting by these different modes of action bound to distinct sites on CD73. All selected antibodies cross-react with cynomolgus CD73 protein and have strong avidity and affinity for membrane or recombinant CD73, by flow cytometry and Surface Plasmon Resonance, respectively. Antibodies that inhibit CD73 enzymatic activity strongly reduce AMP catabolism by both recombinant and cellular CD73 with IC50 in the nanomolar range. They also efficiently reverse ATP- and AMP-mediated T cell suppression in in vitro assays in presence of both CD39 + and CD73 + cells. The antibodies that induce down-modulation of cellular CD73 expression do not block recombinant CD73 enzyme activity and partially inhibit cellular CD73 activity; they reverse ATP- but not AMP-dependent T cell suppression. The antibodies displaying the most interesting features were humanized. Evaluation of their activity in animal models is ongoing. Citation Format: Marc Giraudon Paoli, Severine Augier, Marilyne Royannez Blemont, Celine Rodriguez, Helene Rispaud Blanc, Stephanie Chanteux, Nicolas Gourdin, Laurent Gauthier, Christine Menetrier Caux, Yannis Morel, Christophe Caux, Carine Paturel, Ivan Perrot. Discovery and characterization of new original blocking antibodies targeting the CD73 immune checkpoint for cancer immunotherapy. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 2344.