Immune cell signaling proteins, known as cytokines, are highly toxic—not just to tumors but, unfortunately, to healthy tissue as well. Wittrup Lab researchers are delivering cytokines directly into solid tumors and using the collagen-binding protein lumican to confine these cell-killing proteins within the tumoral space. Their strategy, described in Science Translational Medicine, leverages the protective layer of collagen produced by the cancer cells to prevent leakage of these toxic agents into the bloodstream and opens up previously-closed avenues for combination immunotherapy.