All NB cell lines treated with IFNγ and TNFα showed a strong upregulation of IDO1 (Figure 3E), indicating that the treatment with these cytokines, although it resulted in an increased Fas expression and consequently enhanced NK-cell-mediated apoptosis of NB cell lines, controlled the NK-cell-mediated recognition process through IDO1-dependent immune evasion mechanisms, thereby attenuating the NK-cell-mediated killing. Here, TNF is linked to neuroblastoma.