Using natural killers from the immune system to target breast cancer cells It sounds like a plot from a Quentin Tarantino movie -- something sets off natural killers and sends them on a killing spree. But instead of characters in a movie, these natural killers are part of the human immune system and their targets are breast cancer tumor cells. The triggers are fusion proteins developed by Clemson University researchers that link the two together. The idea is to use this bifunctional protein to bridge the natural killer cells and breast cancer tumor cells. If the two cells are brought close enough together through this receptor ligand connection, the natural killer cells can release what I call killing machinery to have the tumor cells killed."