Next, to explore further mechanisms of immune evasion leading to the impaired NK cell degranulation in response to cytokine-treated NB cells, we assessed the expression level of Indoleamine-pyrrole 2,3-dioxygenase1 (IDO1), an enzyme involved in mechanisms conferring resistance to immune cell activities in most tumors [66], including NB as we previously reported [67]. The gene discussed is IDO1; the disease is neuroblastoma.