Possibly, potent NKG2D down-modulation by TGF-β (see below) in serum samples of cancer patients containing both TGF-β and sNKG2DL may have led to some erroneous conclusions regarding sNKG2DL-mediated NKG2D down-modulation in previous studies (15, 92–94). Here, KLRK1 is linked to cancer.