Abstract 6370: Cell-based Luminescent Reporter Bioassays for Immunotherapies Targeting Macrophage Effector Functions

Abstract Macrophages play a key role in the elimination of cancer via phagocytosis and presentation of tumor antigens to T cells. Antibody-dependent cellular phagocytosis (ADCP), mediated by macrophages and other myeloid cells, is an important mechanism-of-action (MoA) for antibody-based cancer immunotherapies. Therapeutic strategies that enhance ADCP and other macrophage effector functions can augment direct tumor destruction and enable anti-tumor immunity. ADCP is initiated by binding of antibody Fc domains to Fc gamma receptors (FcgRs), and FcgR crosslinking results in signal transduction that drives inflammatory cytokine production and phagocytosis. Simultaneously, macrophage effector functions are regulated by immune checkpoints. Blockade of these immune checkpoints (e.g., SIRPa, ILT4), or agonists of activation pathways (e.g., TLR receptors) can enhance macrophage effector functions. Current assays to measure macrophage function are tedious, low throughput, and highly variable. Here, we present a suite of cell-based luminescent reporter bioassays to measure macrophage effector functions: 1) A monocytic cell background was used to measure ADCP via endogenous expression of multiple FcgRs and integration of a FcgR-activation dependent luminescent reporter. 2) Direct detection of cellular phagocytosis can be measured using the HiBiT split luciferase system. 3) Modulation of macrophage-expressed immune checkpoints can be determined using cell-based reporter bioassays for SIRPa/CD47 and ILT4/HLA-G. 4) Activation of TLRs 1, 2, 4, 5 and 6 can be measured using a TLR reporter bioassay. These bioassays are robust, easy-to-use, and are pre-qualified according to ICH guidelines. Together, these novel reporter bioassays provide a robust, high-throughput toolbox to facilitate discovery and development of immunotherapies targeting macrophage effector functions. Citation Format: Jonathan Mitchell, Julia Gilden, Jim Hartnett, Pete Stecha, Gopal B. Krishnan, Frank Fan, Mei Cong, Jamison Grailer. Cell-based luminescent reporter bioassays for immunotherapies targeting macrophage effector functions. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 6370.