It should be considered that the presence of cells able to produce these cytokines may play a dual role in tumor control, possibly eliciting negative feedback mechanisms, such as the increased transcription of the immunosuppressive enzyme Indoleamine-pyrrole 2,3-dioxygenase (IDO) by tumor cells in the presence of IFN-γ release [54,55]. The gene discussed is IFNG; the disease is neoplasm.