Abstract 3190: Twin Fc-immune cell engager (ICE): A novel antibody platform for cancer immunotherapy with enhanced avidity for Fcγ receptors and complement
Authors: Choi Eun Shik , Park Hyunkyu , Bae Jiseon , Lee Ki-June , Kim Eunmi , Yoon Sujin , Lee Deokjae , Yang Gi-Hyeok 
Published: March 2024

Abstract
Immunoglobulin G (IgG)-based mAbs have become a dominant class of cancer immunotherapy due to their excellent drug-like properties, long half-life, and generally safe profiles. Typical IgG-based therapeutic mAbs have strong binding to target antigens owing to the valency effect of two antigen-binding fragments (Fabs). However, the single crystallizable fragment (Fc) lacks the valency effect to engage immune effector elements. As Fcγ receptors (FcγR) such as FcγRIIa and FcγRIIIa and C1q complement component have low affinity for Fc, IgG-based mAbs require high antibody opsonization density to exhibit avidity for these low affinity Fcγ receptors and C1q. This may also account for the suboptimal efficacy of IgG-based mAbs against tumors with less abundant antigen. To enhance effector functions of IgG1 by overcoming such limitation, we devised a novel platform, Twin Fc-ICE, in which a single Fab region is attached by two Fc regions which allow for high avidity binding to Fcγ receptors and C1q. The two Fc regions of Twin Fc-ICE are arranged in parallel, not in tandem, to adopt natural topologies of multiple Fc regions presented by IgG1-opsonized targets. Supporting the avidity effect of Twin Fc-ICE for FcγR binding, we showed that CTN001, a Twin Fc-ICE with trastuzumab Fab, have markedly increased binding to FcγRs including FcγRI, FcγRIIa and FcγRIIIa compared with trastuzumab. The avid FcγR binding was further demonstrated by flow cytometry analysis of human blood which revealed significantly increased binding of CTN001 relative to trastuzumab for immune cells expressing activating FcγRs such as natural killer (NK) cells, monocytes, and dendritic cells (DCs). The monovalent antigen binding of Twin Fc-ICE requires Fab with high affinity. However, provided that high affinity is achieved, the monovalent Fab adds to the two Fc regions to maximize the Fc load on cancer cells expressing low levels of antigen. Indeed, flow cytometry analysis revealed that treatment of CTN001 alone results in higher Fc load on HER2-expressing cancer cells than combination of two anti-HER2 IgG1 mAbs, trastuzumab and pertuzumab. In consistent with increased Fc load on target cells and avid FcγR binding, CTN001 induces enhanced effector functions such as CDC, ADCC and ADCP against HER2-expressing cancer cells compared with trastuzumab, which will be presented in a separate poster. CTN001 exhibits comparable thermal stability with trastuzumab and can be readily purified to &gt;95% purity with typical purification platforms. The serum half-life of CTN001 at 10 mg/kg intravenous dose in rats is found non-inferior to that of trastuzumab (~12 days versus ~7 days). Taken together, Twin Fc-ICE provides an optimized platform with drug-like properties, which leverages avidity effects of Fc to potentiate therapeutic efficacy of antibody.
Citation Format: Eun Shik Choi, Hyunkyu Park, Jiseon Bae, Ki-June Lee, Eunmi Kim, Sujin Yoon, Deokjae Lee, Gi-Hyeok Yang. Twin Fc-immune cell engager (ICE): A novel antibody platform for cancer immunotherapy with enhanced avidity for Fcγ receptors and complement [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 3190.