Abstract 2775: A novel immunostimulatory OX40/PD-L1 bivalent bispecific antibody (MEDI1109) for the treatment of patients with cancer

Targeted immunotherapy utilizing agonist antibodies (Ab) to OX40 shows great promise in preclinical mouse models alone or in combination with various therapies including PD1/PD-L1 antagonist Abs. Ab-mediated signaling through OX40 requires higher-order clustering by Fcγ receptors to co-stimulate antitumor-specific T cells and attenuate regulatory T cell (Treg) immunosuppression, leading to antitumor activity. To date, OX40 agonists are well-tolerated but show limited activity alone or in combination with checkpoint blockade in clinical trials. We hypothesize that the antitumor activity of OX40 agonists in patients may be limited by insufficient intratumoral exposure and an inadequate amount of clustering by Fcγ receptors within the tumor microenvironment. To overcome these limitations, we engineered MEDI1109, a bivalent bispecific Ab composed of an OX40 agonist Ab molecularly fused to two single-chain variable fragments derived from a PD-L1 antagonist. The resulting bispecific Ab retained the functional properties of each parent Ab that included binding and agonizing OX40, binding and full blockage of the PD-L1/PD-1 pathway, depletion of OX40+ Tregs and overcoming Treg suppression. Emerging data suggest that the bispecific Ab also drives novel biology including (1) increased OX40 agonism through clustering by either PD-L1 and Fcγ receptors, (2) improved intratumoral exposure through PD-L1 targeting, (3) elimination of PD-L1 positive tumor cells by NK cell mediated antibody-dependent cellular cytotoxicity and (4) enhanced antitumor immunity through concurrent PD-L1/PD-1 blockade on tumor cells and OX40 co-stimulation of antitumor T cells. Intravenous administration of OX40/PD-L1 bispecific Abs to cynomolgus monkeys resulted in the proliferation of peripheral blood CD4+ and CD8+ total memory T-cell populations, and in the reduction of soluble PD-L1 levels in the plasma. These results demonstrate that MEDI1109 is a unique and potent immune modulating agent and may be utilized to enhance antitumor immunity in patients with cancer. Citation Format: Michael D. Oberst, Srinath Kasturirangan, Clifford Sachs, Catherine Auge, James Moynihan, Raymond Rothstein, James Hair, Francis Neal, Srinivas Mamidi, Shino Hanabuchi, Amanda Watkins, Yanan Zheng, Kim Rosenthal, Daniel J. Freeman, Scott Hammond. A novel immunostimulatory OX40/PD-L1 bivalent bispecific antibody (MEDI1109) for the treatment of patients with cancer [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 2775.