Abstract 2782: Examining the dynamic regulation of OX40 following receptor agonism and T-cell activation: Implications for antibody-mediated enhancement of T-cell function

Background: Following the clinical success of checkpoint blockade with CTLA-4 and PD-1 pathway-targeted agents, the field of cancer immunotherapy is rapidly expanding. Costimulatory molecules from the tumor necrosis factor receptor superfamily (TNFRSF), including OX40, may be promising targets to enhance the benefits of immunotherapy. While the functional consequences of signaling through OX40, either via OX40 ligand or agonistic antibodies, have been well documented, little attention has been paid to the temporal regulation of the OX40 receptor itself following T-cell activation and receptor agonism. Here we present functional characterization of BMS-986178, a fully human IgG1 monoclonal OX40- agonistic antibody. Methods: We developed in vitro assays using healthy donor human CD4 + effector T (Teff) and regulatory T (Treg) cells to (1) characterize the functional activity of BMS-986178 across a wide range of concentrations (0.0001-200 nM), (2) address how OX40 receptor expression is modulated following T-cell activation, and (3) determine whether antibody treatment affects receptor regulation. Analysis of murine tumor-infiltrating lymphocytes (TILs) allowed for the comparison of receptor regulation across species. Results: BMS-986178-mediated enhancement of human CD4 + Teff responses and reversal of Treg suppression was dependent on antibody cross-linking, as activity was lost in the absence of FcγR- or secondary antibody-mediated cross-linking in the assays. Maximal increases in activation markers (CD25, ICOS), proliferation, and cytokine production mediated by BMS-986178 treatment occurred at ≈20% receptor occupancy (RO). This functional enhancement was lost at relatively high antibody concentrations (>1 nM) associated with full RO. Lower concentrations of BMS-986178 (0.001-0.3 nM) were sufficient to drive upregulation of OX40, both on the cell surface and the soluble receptor; however, as RO approached 100%, a loss in surface and soluble OX40 was observed. Loss of receptor at the point of full RO was also observed in murine TILs. The downregulation of OX40 was specific to treatment with BMS-981678, as it was not observed with anti-CD28 or antibodies against other TNFRSF members. Internalization of the receptor:antibody complex as well as epigenetic regulation of the OX40 locus were examined for their role in receptor downregulation. Conclusions: These results demonstrate a clear relationship between RO and the ability of BMS-986178, an agonist OX40 antibody, to enhance T-cell responses. Furthermore, these findings provide insight into antibody-mediated receptor modulation in vitro, with potential implications for defining the optimal dose and schedule of agonist OX40 antibodies and, perhaps more broadly, for agonists targeting other costimulatory molecules. Citation Format: Marie-Claude Gaudreau, Christina Milburn, Chan Gao, Alla Pritsker, Mark Fereshteh, Zheng Yang, Bryan Barnhart, Alan Korman, Michael Quigley. Examining the dynamic regulation of OX40 following receptor agonism and T-cell activation: Implications for antibody-mediated enhancement of T-cell function [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 2782.