IDO1 and head and neck squamous cell carcinoma: Expression of immune modulatory factors (c-kitL, COX2, FLT3L, GM-CSF, IL-1β, IL-4, IL-6, IL-10, IDO, iNOS, M-CSF, TGFβ, TNFα, VEGF) was measured in eight HNSCC cell lines using quantitative RT-PCR techniques.