Natural Killer (NK) cells are lymphocytes of the immune system that are critical in host defense and immune regulation as part of both the innate and adaptive immune response They are of particular interest to immunotherapy researchers as they hold the promise to specifically target and destroy cancer cells and tumors while leaving healthy cells intact Natural Killer cells are traditionally characterized by the presence of the CD56 cell surface marker and absence of CD3 In addition CD16 is important for NK cell function because CD16 induces cytokine expression and cytotoxic effector activity Lonza NK cells are isolated using positive (2W-502) or negative (2W-501) immunomagnetic selection for the CD56 marker Purity is 90% based on the presence of CD56 cells Both positively and negatively selected NK cells are guaranteed to express CD56 and CD16