Review of methionine manipulation in solid tumor immunotherapy settingsDoctors explore changing methionine levels to help immune cells fight solid tumors better

T cell–based immunotherapies have transformed cancer treatment, yet their efficacy in solid tumors is constrained by the nutrient-poor and oxidative tumor microenvironment (TME). Accumulating evidence indicates that reactive oxygen species (ROS), methionine metabolism, and the amino acid stress sensor general control nonderepressible 2 (GCN2) are tightly interconnected regulators of T cell activation, differentiation, and effector function. In this review, we detail how these pathways form an integrated redox–metabolic circuit that dynamically tunes T cell responses to environmental stress. Physiological ROS are essential for T cell receptor signaling, glycolytic reprogramming, and cytotoxicity, whereas excessive or prolonged oxidative stress drives exhaustion and apoptosis. GCN2 links amino acid availability, particularly methionine and cysteine, to adaptive transcriptional and metabolic programs that regulate glutathione synthesis and redox homeostasis. We highlight how therapeutic manipulation of methionine availability, GCN2 signaling and ROS produces highly context-dependent outcomes across immune checkpoint blockade and adoptive cell therapy settings in solid tumors. Finally, we discuss emerging strategies to interrogate and modulate this circuit using integrated omics, CRISPR-based screening, and pharmacological approaches, emphasizing the need for context-aware and temporally controlled metabolic interventions to enhance T cell–based immunotherapies in solid tumors.