From barrier to trigger: leveraging tumor hypoxia for precise control of CAR-T cell activity

CAR-T cell therapy has revolutionized the treatment of hematologic malignancies, yet its translation to solid tumors remains a formidable challenge. A central determinant of this limitation is the hypoxic tumor microenvironment, which imposes profound immunosuppressive pressure on infiltrating CAR-T cells, impairing their persistence, effector function, and metabolic fitness. Rather than viewing hypoxia purely as an obstacle, emerging engineering paradigms are reframing it as a tumor-selective switch one that can be harnessed to spatially confine CAR-T cell activation, enhance metabolic fitness, and reduce off-tumor toxicity. This review critically examines how hypoxia subverts CAR-T cell immunity, and how next-generation hypoxia-responsive constructs, metabolic reprogramming strategies, and armored cytokine-secreting designs are beginning to turn this hostile microenvironment into a therapeutic advantage. We further discuss unresolved clinical challenges and the translational outlook for hypoxia-adapted CAR-T cells in solid tumor immunotherapy.