Abstract 2634: CRISPR in vivo screen utilizing removable Cas9 system to identify epigenetic immune response modulators in antigen-sensitive mouse syngeneic models

Abstract The application of CRISPR-Cas9 screen in tumor immunology research has promoted the discovery of potential therapeutic targets and provided a deeper understanding of the mechanisms of immunotherapy resistance. Mouse syngeneic tumor model based CRISPR in vivo screen revealed significant features of immunotherapy by better approaching the tumor immune interaction. However, the immunogenicity of CRISPR-Cas9 has been widely observed in a variety of syngeneic models, which greatly limited for the application of CRISPR in vivo screen. Herein, we used two strategies for cancer cell gene editing, Cas9 protein electroporation and loxP-flanked Cas9 with Cre recombinase, to reduce the immunogenicity of CRISPR-Cas9 in CT26 subcutaneous and Renca orthotropic syngeneic models. Encouragingly, we found out that compared with constitutive Cas9-expressing All-In-One based cell pool models, both CT26 subcutaneous model and Renca orthotropic model showed a parental cell tumor comparable growth kinetics and immune checkpoint blockade ICB response by PD-1 antibody treatment. Further immuno-profiling of tumor immune microenvironment indicated limited changes from the parental cell model, which helped the data interpretation of in vivo screen outcome. We then performed a CRISPR in vivo screen by using a focused library against mouse epigenetic regulators in these two models and will discuss the hits from the screen in future. Citation Format: Yuan He, Yafei Liu, Xiao Wang, Xianyi Li, Wenle Dong, Tongrui Hao, Chenyang Zhu, Wenrong Zhou, Zhengang Peng. CRISPR in vivo screen utilizing removable Cas9 system to identify epigenetic immune response modulators in antigen-sensitive mouse syngeneic models [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 2634.