Abstract 4275: Agonist OX40 ligand fusion proteins induce effector T cell proliferation, block regulatory T cell function and can combine with immune checkpoint inhibitors to promote antitumor immunity in preclinical models

Proceedings: AACR 106th Annual Meeting 2015; April 18-22, 2015; Philadelphia, PA OX40 is a tumor necrosis factor receptor found primarily on activated T effector (Teff) cells and regulatory T (Treg) cells including lymphocytes infiltrating mouse and human tumors. Costimulation of OX40 by agonist molecules is hypothesized to improve antitumor immunity by enhancing Teff cell activity and inhibiting Treg suppression. We conducted in vitro and in vivo experiments to characterize the costimulatory activity, assess single agent and combination antitumor efficacy and measure pharmacodynamic biomarkers of novel, agonist OX40 ligand (OX40L) fusion proteins. In vitro costimulation assays, Treg suppression studies, and human tumor/T cell xenograft mouse models were performed using MEDI6383, a human OX40L fusion protein. MEDI6383 is comprised of three distinct domains: (1) human OX40L extracellular receptor binding domains, (2) isoleucine zipper trimerization domains, and (3) human fragment crystallizable gamma (Fcγ) domains. In vivo antitumor activity was evaluated using a surrogate mouse OX40L fusion protein (mOX40L FP), and anti-mouse PD-L1, anti-mouse PD-1 or anti-mouse CTLA-4 monoclonal antibodies in multiple syngeneic mouse tumor models. MEDI6383 activated the OX40 signaling pathway, as measured by NFκB signaling, in human OX40-expressing Jurkat T reporter cells co-cultured with cells that express Fcγ receptors. With concurrent CD3 stimulation, MEDI6383 costimulated primary human Teff cells to proliferate and release cytokines, and suppressed Treg cell activity in T cell co-cultures. MEDI6383 demonstrated potent in vivo antitumor activity that was dependent on the addition of alloreactive human T cells in a mouse model of human cancer. Administration of mOX40L FP resulted in dose-dependent antitumor activity that significantly reduced growth of 4 histologically distinct mouse tumor models. Antitumor activity of mOX40L FP and increases in T-cell proliferation was dependent on the expression of activating Fcγ receptors but not the inhibitory Fcγ receptor. Checkpoint inhibitors combined with mOX40L FP resulted in significantly greater antitumor activity of established tumors than either antibody used as monotherapy. These results demonstrate that agonist OX40L fusion proteins induce potent T cell proliferation, block Treg inhibition and promote antitumor activity in preclinical models as a single agent or in combination. Citation Format: Kelly McGlinchey, Kathy Mulgrew, Chad Morris, Catherine Auge, Nicholas Holoweckyj, Nicholas Durham, Karen Coffman, James Hair, Terrance O'Day, Nicholas Morris, Andrew Weinberg, Ching Ching Leow, Michael Oberst, Scott A. Hammond. Agonist OX40 ligand fusion proteins induce effector T cell proliferation, block regulatory T cell function and can combine with immune checkpoint inhibitors to promote antitumor immunity in preclinical models. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 4275. doi:10.1158/1538-7445.AM2015-4275