Cancer immunotherapy has revolutionized treatment for patients, whereby the body's own immune system is harnessed to destroy cancer cells. Typically, several molecules restrain the ability of T cells to target cancer cells and developing approaches to limit this restraining effect can lead to improved effectiveness of cancer immunotherapy. Research has now determined the structure of how an inhibitory molecule, LAG3, interacts with its main ligand and provides a new targeted approach to improving the effectiveness of immunotherapy for certain forms of cancer.