T Cell Exhaustion: Chronic Stimulation and the Exhaustion Hierarchy

When a CD8⁺ T cell faces antigen that never clears — a chronic viral infection or a persistent tumor — it doesn't stay effective forever. Continuous receptor signaling drives it down a well-characterized path called exhaustion: inhibitory receptors like PD-1, LAG-3, TIM-3 and TIGIT accumulate, and effector functions shut off one by one in a fixed order (IL-2, then TNF-α, then IFN-γ, then cytotoxicity last). This 2D simulation tracks that trajectory for a single T cell in real time — a live radar chart of its four effector functions, a bar readout of its inhibitory-receptor load, and a shrinking/regrowing tumor mass driven by whatever cytotoxic capacity remains — and lets you test the central clinical question behind checkpoint-inhibitor immunotherapy: does blocking PD-1 still work? The model enforces a biologically real answer — reinvigoration only happens while the cell is still progenitor-exhausted and hasn't crossed the epigenetic fixation point; once it goes terminal, it stays locked out no matter the dose.