TLR7 and head and neck squamous cell carcinoma: pDCs, the major producer of IFN-I in HNSCC, detect antigenic RNA and DNA through TLR7 and TLR9, respectively (35–38), and signal through TLR7/9-MyD88-NF-kB pathway (39), leading to pDC maturation, and the secretion of IFN-I (40).