Our immune systems are at war with cancer. This animation reveals how monoclonal antibodies can act as valuable reinforcements to shore up our defences – and help battle cancer. You can find more on this topic at http://www.nature.com/milestones/antibodies Nature Research has full responsibility for all editorial content, including Nature Video content. This content is editorially independent of sponsors. Sign up for the Nature Briefing: An essential round-up of science news, opinion and analysis, free in your inbox every weekday. https://go.nature.com/371OcVF