An interdisciplinary team of scientists from the Berlin Institute of Health at Charité (BIH), the Max Delbrück Center, the German Cancer Research Center (DKFZ), the Heidelberg Institute for Stem Cell Technology and Experimental Medicine (HI-STEM) and Queen Mary University of London, UK, has developed a technology to decode immune cell communication. By measuring interactions between cells, the method offers insights into how the human body fights viral infections, how malfunctions can lead to autoimmune diseases and why immunotherapies work for some people but not others.