CTLA-4 Checkpoint Blockade: Competitive Receptor Binding

At the immune synapse between a T cell and an antigen-presenting cell, CD28 and CTLA-4 compete head-to-head for the same B7 ligand molecules — one delivers a costimulatory "go" signal, the other an inhibitory checkpoint "stop" signal. This simulator models that competition as a per-molecule stochastic process governed by real Langmuir binding kinetics (k_on, k_off, K_d), with CTLA-4's much slower off-rate letting it capture a disproportionate share of the shared ligand pool despite similar binding speed. Dial in an anti-CTLA-4 checkpoint-inhibitor antibody and watch it sterically block CTLA-4 receptors, freeing B7 for CD28 and shifting the live activation-index readout toward T-cell costimulation — the actual mechanism behind CTLA-4-targeted cancer immunotherapy.