Compartment-specific PPARδ activity controls the outcome of cancer–immune cell competition and immunotherapy efficacy

T cells sensitize immunotherapy-resistant microsatellite stable metastatic colorectal cancer to checkpoint blockade in mice, and pharmacological or genetic PPARδ activation enhances human chimeric antigen receptor T cell function. These findings identify compartment-specific PPARδ activity as a targetable driver of immune cell fitness that can be harnessed to improve outcomes in immunotherapy-resistant tumors.