In vivo genome-wide CRISPR screens identify FOXR1 as a suppressor of CD8+ T cell anti-tumor immunity [ATAC-Seq]

Through an in vivo genome-wide CRISPR screen in tumor-infiltrating CD8+ T cells, we identified the Forkhead Box R1 (FOXR1) as a potent transcriptional suppressor of CD8+ T cell effector functions. Genetic ablation of FOXR1 significantly enhanced cytokine production and cytotoxic capacity in both murine and human CD8+ T cells, whereas its overexpression impaired T cell activation and effector molecule expression.

Mechanistically, multi-omics integration of RNA-seq, CUT&Tag, and ATAC-seq revealed that FOXR1 binds directly to promoter regions of key effector genes, including IL2, GZMB, and PRF1, repressing their expression by restricting chromatin accessibility. Importantly, FOXR1 deletion in human anti-CD19 CAR T cells improved their efficacy against solid tumors, demonstrating FOXR1 as a previously unrecognized checkpoint of T cell effector function and its targeting as a promising strategy to enhance CAR T cell efficacy against solid tumors.