Similarly, PD‐1, a member of the extended CD28/CTLA4 family of T‐cell regulators, is expressed by activated T cells where it binds to the PD‐1 ligand expressed by tumours and APCs to inhibit T‐cell effector function, a reversible process termed T‐cell ‘exhaustion’ [46]. The gene discussed is CD28; the disease is neoplasm.