T-cell exhaustion

T-cell exhaustion is a worn-out, underperforming state that your antigen-specific T cells (mainly CD8+ killer T cells) fall into when an antigen sticks around too long, as in chronic viral infections (HIV, HBV, HCV) or in tumors. The cells lose their functions in a set order. IL-2 secretion fails first, then TNF-α, then IFN-γ; and their ability to multiply and kill steadily fades. Exhausted T cells display multiple inhibitory 'checkpoint' receptors at once (PD-1, TIM-3, LAG-3, CTLA-4), which defines them. Wherry et al. (2007, Immunity) mapped these receptors, plus metabolic and signaling defects, in a chronic mouse virus model. Persistent T-cell-receptor signaling switches on a transcription factor (TOX). Khan et al. (2019, Nature) showed TOX locks in an exhaustion-specific chromatin state through epigenetic remodeling, making the condition largely irreversible and only partly rescued by checkpoint-blocking drugs. Exhaustion is distinct from T-cell senescence: senescent cells are permanently arrested (with SA-β-gal and p16/p21), while exhausted cells keep some proliferative potential. CMV positivity (in about 40 to 80% of older adults) drives a clonal inflation of Tim-3+PD-1+ T cells that build up even without active infection (Lee et al., 2016, Aging Cell). In cancer, how deeply the tumor's T cells are exhausted predicts the response to checkpoint-blockade drugs, since the TOX-driven epigenetic lock-in limits their revival.

Last reviewed: June 22, 2026

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