Tumor Microenvironment-Driven CD8⁺ T Cell Exhaustion: Mechanisms, Therapeutic Implications, and Strategies for Reinvigoration

CD8⁺ T cell exhaustion is a dysfunctional state that arises under chronic antigen exposure within the immunosuppressive tumor microenvironment (TME). It represents a major barrier to the durable efficacy of cancer immunotherapies, including immune checkpoint blockade and adoptive cell transfer. Exhaustion constitutes a distinct and heterogeneous lineage, comprising progenitor-like subsets that retain proliferative capacity and responsiveness to therapy, and terminally exhausted subsets with limited potential for reinvigoration. Multiple TME factors—including hypoxia, nutrient deprivation, accumulation of toxic metabolites, chronic adrenergic stress, and interactions with stromal and myeloid cells—drive and stabilize exhaustion by altering T cell signaling, metabolism, and epigenetic regulation. These extrinsic cues induce exhaustion-specific transcriptional networks (e.g., TOX and NR4A) and stable chromatin remodeling. Immunotherapy response critically depends on the balance between progenitor and terminally exhausted subsets. Emerging therapeutic strategies to overcome exhaustion involve metabolic and hypoxia-targeting interventions, epigenetic modulation, engineered cytokines (e.g., IL‑10–Fc), costimulatory agonism, and T cell-intrinsic engineering. This review synthesizes mechanistic advances in understanding how the TME drives T cell exhaustion and its implications for immune-based therapies.