EMSA (Fig. 2b, c) demonstrated the activation of the transcription factors STAT1, NF-κB, and IRF-1 in response to the treatment with IFNγ, suggesting an important role for these transcription factors in the modulation of IFNγ- induced IDO expression and its consequences in HNSCC cells. Here, IDO1 is linked to head and neck squamous cell carcinoma.