Abstract 3767: Enhanced anti-tumor efficacy through prolonged plasma membrane retention of a novel anti-CCR8/IL2 mutein fusion antibody

Abstract Background: Infiltrating regulatory T cells (Tregs) are part of the tolerogenic microenvironment of tumors and key players in resistance to immune checkpoint inhibitor (ICI) therapy. Selective depletion of Tregs within the tumor microenvironment has the potential to overcome this resistance and to increase the proportion of patients responding to immunotherapy. The CCR8 chemokine receptor, which is preferentially upregulated on tumor-resident Tregs, represents an attractive and specific target for antibody-dependent cell cytotoxicity (ADCC)-mediated Treg depletion. Several ADCC-enhanced anti-CCR8 antibodies are currently being evaluated in clinical trials to assess their therapeutic potential. Our findings suggest that rapid internalization of anti-human CCR8 antibodies upon receptor binding significantly hampers their ADCC efficacy. To address this limitation, we engineered EGL-002, a novel anti-CCR8 antibody fused to an IL2 mutein designed to preferentially block the CD25 receptor and to prevent CCR8 internalization. Methods: Retention of EGL-002 on the plasma membrane was assessed through microscopy and flow cytometry using in vitro-expanded and tumor-infiltrating human Tregs. ADCC and antibody-dependent cellular phagocytosis (ADCP) potency were evaluated in reporter assays and confirmed using donor-derived natural killer (NK) cells and macrophages, respectively. Pharmacodynamics, biodistribution, and anti-tumor activity were evaluated in tumor-bearing mice genetically engineered to express the human target receptors. Treg-depleting activity and specificity were further confirmed in human tumor samples. Results: EGL-002 demonstrated prolonged retention on the plasma membrane of Tregs across in vitro, ex vivo, and in vivo models, compared to the parental antibody. This resulted in enhanced ADCC and ADCP potency, leading to complete Treg depletion in tumors while sparing other tumor-infiltrating effector T cell populations as well as Tregs in the periphery. In mouse models, EGL-002 effectively depleted tumor Tregs, achieving robust anti-tumor efficacy as single-agent and in combination with anti-PD-1 therapy. Conclusion: Preclinical data highlight EGL-002 as a highly effective tumor Treg-depleting agent with potent anti-tumor activity. Its unique design positions it as a best-in-class therapeutic candidate for solid tumors, either as a standalone treatment or in combination with ICIs. Citation Format: Andrés Zucchetti, Benjamin Pelletier, Fabien Delisle, Béré Diallo, Anupama Karnam, Marco Pretti, Erica Russo, Caroline Janot-Sardet, Yann Courbebaisse, Elsa Lheriteau, Charlotte Muller, Marine Dubois, Reno Winter, Mercedes Tkach, Alvaro Lladser, Jonathan Back, Bernard Vanhove, Sébastien Lemoine, Monica Gostissa, Eliane Piaggio, Ilgar Mamedov, Fiorella Kotsias. Enhanced anti-tumor efficacy through prolonged plasma membrane retention of a novel anti-CCR8/IL2 mutein fusion antibody [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 1 (Regular Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_1):Abstract nr 3767.