Many terrible modern diseases, including AIDS and leukemia, affect the cells of the immune system – the body’s natural defenders. Understanding and combating these diseases has been extremely difficult, in part because immune cells are resistant to the strategies conventionally used for interrogating the inner workings of cells. Here, researchers have developed a clever solution: they use tiny needles to inject compounds into immune cells from leukemia patients so that they can identify what drives these cancers and how they can be better treated.