Abstract 5371: Multimodal CRISPR activation screens reveal new mechanisms to sensitize cancer cells to targeted T cell mediated elimination

Abstract Cell autonomous resistance mechanisms can protect cancer cells from targeted T cell elimination, resulting in resistance to a broad range of immunotherapies. High-throughput gene knockout and gene inhibition screens have been instrumental in identifying key drivers of such mechanisms, yet often uncovering gene activity that is essential but not sufficient for response. Here we set out to leverage gene activation as an orthogonal approach to identify novel regulators of the cancer-immune interface. First, we performed CRISPR activation screens in melanoma cells co-cultured with antigen-specific primary CD8+ T cells. Our findings revealed a collection of novel genes that substantially sensitize melanoma cells to targeted T cell-driven elimination when activated, including DNA damage and unfolded protein response genes (e.g., ETS1, TSPYL2), Wnt ligands (e.g., WNT3A, WNT1), and others that are deleterious only in combination with targeting T cells. Among the resistance genes we found regulators of insulin signaling (e.g., HGF, TCF7L2) and numerous glycoproteins (e.g., PDPN, CD44). Second, we validated top novel hits in 2D and in 3D spheroid models, using optical readouts to investigate their impact on cancer cell elimination and cancer-T-cell spatial dynamics. Third, we performed a Perturb-seq screen to stratify dozens of hits into functional groups based on the transcriptional readouts in the cancer cells. Lastly, we developed an in situ Perturb-Seq method, where we combine high-plex spatial transcriptomic readouts at subcellular resolution with in situ detection of genetically modified cells, and applied it to track the impact of the (de)sensitizing perturbations not only on the cancer cells themselves, but also on T cell recruitment and suppression. Taken together, our study provides a catalog of immune evasion mechanisms and an array of novel targets, demonstrating that synthetic gene activation can diminish immune evasion and open novel avenues for development of agonist-based and RNA-based interventions. Citation Format: Reece V. Akana, Chang Sun, YoungMin Kim, Yuxin Cai, Subin Kim, Jeehyun Yoe, Olivia Laveroni, Livnat Jerby-Arnon. Multimodal CRISPR activation screens reveal new mechanisms to sensitize cancer cells to targeted T cell mediated elimination [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 5371.