Treatments for beating tumors are mainly based on CD8 T lymphocytes, which specialize in detecting and eliminating intracellular infections and in killing cancer cells. A large proportion of patients, however, do not respond to these treatments. This prompted a research team from the Swiss Cancer Centre Léman (SCCL, Switzerland) to bring together the universities of Geneva (UNIGE) and Lausanne (UNIL), the Ludwig Institute for Cancer Research (LICR), EPFL and CHUV to investigate CD4 T lymphocytes. While these play a supporting role with CD8 T cells, their ability to eliminate tumor cells directly has been a matter of controversy. Using innovative nanoimaging technologies designed at the EPFL laboratory, the scientists found that when the CD4 T lymphocytes were put in close contact to the cancer cells, up to a third of them could kill them. This discovery, the subject of an article in Science Advances, is significant and broadens the therapeutic perspectives based on administering CD4 T lymphocytes to patients who are resistant to conventional therapies.