Abstract 2721: Selective FcγR engagement by CTLA-4 antibodies results in increased functional activity

Therapeutic antibodies targeting T cell co-inhibitory pathways, such as cytotoxic T-lymphocyte-associated protein 4 (CTLA-4) and programmed cell death protein-1 (PD-1), have emerged as an important class of cancer therapies. Insights into how different IgG isotypes modulate biological activities of antibodies have opened new avenues to enhance their therapeutic effects. For example, Fc-FcγR interactions have been shown to enhance antibody-directed effector cell activities, as well as antibody-dependent forward signaling into target cells via receptor clustering. Here, we describe a novel FcγR-dependent mechanism for antibodies targeting CTLA-4. Our findings suggest that selective Fc-FcγR binding dramatically improves the quality of the immune synapse, which in turn modifies apical T cell receptor signaling events to increase effector T cell activity. Our data also suggest that subsets of antigen-presenting cells (APCs), expressing FcγRIV in mice and FcγRIIIA in humans are important mediators of this effect. Importantly, we find this mechanism to be independent of regulatory T cell (Treg) depletion. Altogether, we describe a novel mechanism of action that provides a foundation for a new class of Fc-engineered antibodies to enhance antitumor immune responses. Citation Format: Jeremy D. Waight, Dhan Chand, Sylvia Dietrich, Randi Gombos, Thomas Horn, Ana M. Gonzalez, Mariana Manrique, Antoine Tanne, Christopher Dupont, Lukasz Swiech, Ben A. Croker, Jennifer S. Buell, Robert Stein, Alex Duncan, David A. Savitsky, Nicholas S. Wilson. Selective FcγR engagement by CTLA-4 antibodies results in increased functional activity [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 2721.