Cytotoxicity of human NK cells against tumor cells and persistence in vivo following adoptive transfer in immunodeficient mice. Left: NK cytoxicity versus TRAIL-sensitized kidney cancer cells. Right: NK cell persistence in vivo. NK cells were labeled with DiR near infrared dye and imaged every 6-12 hours after intraperitoneal NK cell infusion into CB.17 SCID-beige mice. IL-2 (100 000 U) was administered intraperitoneally every 12 hours. Used with permission from Berg et al.⁴⁶