Abstract 7273: CCR8/CCL1 humanized model for efficacy assessment of CCR8/CCL1-targeting therapies

Abstract Modulation of tumor microenvironment has shown to be a promising approach to treat cancer. Among diverse mechanisms responsible for tumor immunosuppression, those mediated by regulatory T cells (Treg) infiltrating in tumor are well identified and known to reduce the efficacy of anti-tumor therapies. CCR8 has been identified as a potential therapeutic target due to its role in the immunosuppression induced by Treg. CCL1 is the major CCR8 ligand and CCL1 / CCR8 interaction induces STAT3-dependent up-regulation of FoxP3, CD39, IL-10 and Granzyme B, leading to the enhancement of the suppressive activity of Treg cells. A major challenge in the development of new therapeutic approaches relies on the choice of the right preclinical model, which could mimic the complexity of interactions among different cell types and closely predict the effects of therapeutics in humans. The current therapeutic approaches directed towards the CCR8/CCL1 axis target the receptor CCR8, requiring its humanization for assessment of therapeutics displaying species-specific activity. The development of a physiologically relevant model depends, among others, on the maintenance of a proper interaction of the receptor and ligand. CCR8 has 2 ligands in mouse: CCL1 and CCL8. Mouse CCL8 is able to induce specific calcium flux in human CCR8-transfected mouse cells (Islam et al., Nat Immunol, 2011), suggesting that humanization of CCL8 is not mandatory. However, in vitro studies showed that murine CCL1 was unable to interact with human CCR8, leading to the conclusion that the CCR8 / CCL1 axis needs to be humanized. Prior to the mouse model generation, an in vitro functional assessment confirmed the functionality of human CCR8 in murine cells. Herein, we describe a novel CCR8 and CCL1 double humanized model. Briefly, CCR8 and CCL1 were humanized. Both human genes are under the control of their endogenous mouse promoter, enabling physiological and regulated expression (no regulatory elements were altered by the gene editing process), which is key for the interpretation of the data obtained with the model. CCL1 is produced and detected in the serum from CCR8/CCL1 humanized mice. CCR8 was expressed on approximately half of the MC38 tumor infiltrated Tregs, while very low or absent expression was observed on Treg in the periphery (spleen, skin and blood). Expression of human CCR8 enabled activity of CCR8-targeting antibodies, as a collaborator has shown that treatment with a CCR8 antibody induces tumor volume reduction (400mm3 vs. 750mm3) and increased survival (80% vs 30%) 20 days post MC38 inoculation. Therefore, this model is a valuable tool for efficacy assessment of CCR8-targeting drugs, enabling the investigation of immunomodulatory mechanisms at the tumor microenvironment. This is possible because the mouse immune system is functional and its interplay with mouse stroma and tumor cells enables the assessment of a finely regulated microenvironment. Citation Format: Fabiane Sonego, Angela Pappalardo, Gaëlle Martin, Yacine Cherifi, Patricia Isnard Petit, Kader Thiam. CCR8/CCL1 humanized model for efficacy assessment of CCR8/CCL1-targeting therapies [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 7273.