Abstract 962: Novel targeting of tumor-infiltrating TNFR2 Tregs: removing suppression with microenvironment-specific antibodies
Authors: Torrey Heather , Butterworth John , Mera Toshiyuki , Okubo Yoshiaki , Wang Limei , Baum Danielle , Defusco Audrey , Plager Sara , Warden Sarah , Huang Daniel , Vanamee Eva , Foster Rosemary , Faustman Denise L. 
Published: July 2017

Abstract
Background: A recognized and potent subtype of regulatory T cells (Tregs) expresses tumor necrosis factor receptor 2 (TNFR2), a member of the tumor necrosis factor (TNF) superfamily. TNFR2 expressing Tregs are overabundant in human and murine tumors and are the most potent suppressors of host immune responses. In addition, recent data in diverse human tumors show that TNFR2-expressing host T cells are the dominant Tregs in the tumor microenvironment, expressed far in excess of OX40 and GITR. Unlike many tumor markers, TNFR2 has limited expression in the immune system and almost no expression on parenchymal cells. This makes TNFR2 Tregs an attractive target for anticancer therapy.
Methods: We produced monoclonal antibodies to human TNFR2 with the goal of inactivating the potent host Tregs that express TNFR2, competing with the agonism of TNF and inactivating infiltating Tregs of human tumors. Tregs from fresh ovarian ascites fluid were compared to Tregs from normal human blood donors for antibody potency.
Results: Using a 48-hr cell-based Treg assay, we showed that TNFR2 antagonistic antibodies can inhibit Treg proliferation, suppress soluble TNFR2 secretion on normal cells and allow T effector expansion. The antagonism is dominant, succeeding even in the presence of TNF, which is a TNFR2 agonist. Furthermore, the structural biology of dominant TNFR2 receptor antagonism uncovers a unique conformation that equally inhibits downstream NFkB signaling. We also showed that dominant TNFR2 antibodies in a dose dependent fashion kill Tregs in ovarian cancer infiltrates more strongly than Tregs from healthy donors. Treg killing in the cancer microenvironment was dependent on cell proliferation and turnover the Tregs.
Conclusion: In sum, blocking TNFR2 signaling on the most potent Tregs of the tumor microenvironment with a dominant antagonist antibody selectively heightens death of the immunosuppressive Tregs in the tumor microenvironment, at least in ovarian cancer. With the expanding knowledge that TNFR2 Tregs are the most potent host cells of the immune response, their dominance in diverse human tumor infiltrates and the natural low expression of this marker on normal lymphoid cells makes targeting of TNFR2 in the tumor microenvironment attractive.
Citation Format: Heather Torrey, John Butterworth, Toshiyuki Mera, Yoshiaki Okubo, Limei Wang, Danielle Baum, Audrey Defusco, Sara Plager, Sarah Warden, Daniel Huang, Eva Vanamee, Rosemary Foster, Denise L. Faustman. Novel targeting of tumor-infiltrating TNFR2 Tregs: removing suppression with microenvironment-specific antibodies [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 962. doi:10.1158/1538-7445.AM2017-962