Abstract 2214: GITR ligand fusion protein (GITRL-Fc) induces T cell mediated anti-tumor immune response and can combine with anti-PDL1 to enhance anti-tumor immunity and long-term immune memory

Abstract

Abstract GITRL (Glucocorticoid-Induced Tumor Necrosis Factor Receptor Ligand, TNFSF18) is a member of the TNF superfamily and naturally exists as a membrane-anchored type II protein that self assembles as a trimer. GITRL activates the co-stimulatory receptor GITR. GITR is found primarily on activated T effector (Teff) cells and regulatory T (Treg) cells. Co-stimulation of GITR by agonist agents is hypothesized to promote anti-tumor immunity by enhancing Teff cell activity and inhibiting Treg suppression. We generated a novel single-gene GITRL trimer fused to an immunoglobulin Fc domain (GITRL-Fc). GITRL-Fc activated GITR signaling more effectively than prototype GITR agonist antibody DTA-1. GITRL-Fc promoted a robust anti-tumor immune response in multiple syngeneic mouse tumor models. GITRL-Fc enhanced tumor specific T-cell responses, particularly of the Th1 type, and also led to reduction in Treg-mediated immunesuppressive activity. GITRL-Fc displayed single agent activity in inhibiting tumor growth and promoting complete tumor rejection in the murine CT26 colon carcinoma model and combination activity with anti-PDL1 as compared to anti-PDL1 and control IgG2a alone. Mice “cured” with GITRL or GITRL/anti-PDL1 combination treatments were protected from re-challenge with tumor cells, suggesting the existence of immunologic memory. More mice were protected from tumor re-challenge with the combination of GITRL-Fc and anti-PDL1, as compared to GITRL-Fc alone. Our results demonstrate that agonist GITRL-Fc induces potent T cell responses, overcomes Treg inhibition, and promotes anti-tumor activity in preclinical models as a single agent or in combination with anti PDL1. The mechanism of tumor eradication and induction of long-term immune memory response by the combination is under investigation and will be discussed at the presentation. Citation Format: Minu K. Srivastava, Rui Yun, Erin Mayes, Hyun_Bae Jie, Fumiko Axelrod, Jorge Monteon, Ming-Hong Xie, John Lewicki, Tim Hoey, Austin Gurney, Angie Inkyung Park. GITR ligand fusion protein (GITRL-Fc) induces T cell mediated anti-tumor immune response and can combine with anti-PDL1 to enhance anti-tumor immunity and long-term immune memory. [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 2214.