Since NK-cell mediated cytotoxicity is dependent on the tumor cell membrane expression of several ligands that upon engagement with specific NK cell receptors either inhibit or activate NK cell cytotoxic function, the expression of MHC class I (ligand for inhibiting NK receptor Ly49D), Rae1δ, Rae1αβδγε, mult1, H60a, H60b, and H60c (ligands for NKG2D, an activating NK cell receptor) [16–19], as well as of Fas and FasL (molecules involved in programed cell death) was assessed in vitro transformed astrocytes. Here, FAS is linked to neoplasm.