Abstract 2732: Cell-based reporter bioassays to evaluate the Fc gamma receptor-dependent agonistic activities for therapeutic antibodies targeting immune costimulatory receptors

Immune costimulatory receptors synergize with TCR-CD3 signaling to promote cell cycle progression, cytokine production, T cell survival and effector functions. They belong to immunoglobulin super-family (CD28, ICOS) and tumor necrosis factor receptor (TNFR) superfamily (4-1BB, OX40, CD27, CD40, GITR, DR3, and HVEM). Preclinical and clinical evidence shows that agonist antibodies against costimulatory receptors can stimulate antitumor immunity and are emerging as a promising approach for cancer immunotherapies. Furthermore, FcγR engagement, especially FcγRIIB due to its bioavailability, has been shown to provide a crosslinking scaffold for the antibody IgG to facilitate TNFR clustering/activation and become requisites for some agonist antibody activities. Here, we report the development of a suite of cell-based reporter bioassays to quantitatively measure the potencies of therapeutic antibodies designed to target costimulatory receptors. For this, we developed engineered effector cells that express each costimulatory receptor and a luciferase reporter driven by response element that specifically responds to costimulatory receptor signaling. We also developed a FcγR-expressing cell line to evaluate the involvement of FcγR in agonist antibody-mediated costimulatory signaling. The assays are specific for each costimulatory receptor, and can be used to detect both agonistic and blocking activities for the antibodies. When co-incubated with the engineered FcγR-expressing cells, they are able to show the Fcγ receptor-dependent or independent agonist activities. In summary, these reporter bioassays can serve as powerful tools in immunotherapy drug development for antibody screening and potency determination. Citation Format: Jun Wang, Michael Beck, Jamison Grailer, Pete Stecha, Jim Hartnett, Frank Fan, Mei Cong, Zhi-Jie Jey Cheng. Cell-based reporter bioassays to evaluate the Fc gamma receptor-dependent agonistic activities for therapeutic antibodies targeting immune costimulatory receptors [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 2732.