Increased expression of CD39, CD73, and adenosine in the HNSCC patients is thought to be associated with more potent Teff cell suppression.153 HNSCC tumors show an increased number of MDSCs,156 and by producing NO and ROS catalyze the nitration of the T-cell receptor, prevent TCR-HLA interaction and subsequent activation.157 HPV-associated tumors represent a significant proportion of HNSCCs with enhanced production of TGF-β, decreased expression of IFN-α, TLR9, low viremia, infection confined to keratinocytes with no cell lysis that prevents inflammation. This evidence concerns the gene TLR9 and head and neck squamous cell carcinoma.