Our immune T-cells are a type of white blood cell that are crucial to recognise and attack infections and cancerous cells. For this reason, T-cells are important drug targets in vaccines and cancer immunotherapies. A drug currently in pre-clinical development is showing promising results in boosting a key regulator in T-cell functions 500-fold, but how this happens remains a mystery. We hypothesise that the drug increases the active state of the T-cell regulator by inducing a structural change.