It has long been suspected that endothelial cells, the specialized cells lining the inner walls of blood vessels, play a key role in determining how the body's immune system responds to tumors. Researchers at the German Cancer Research Center (DKFZ) in Heidelberg and the Medical Faculty Mannheim of Heidelberg University have now identified, in mouse studies, a specialized population of blood vessel lining endothelial cells that enable an effective immune defense against cancer metastases in the liver. The findings could pave the way for novel combination therapies for cancer.