Additionally, consistent with the immunosuppressive phenotype of human HNSCC-derived CD44hi tCSC, CD44hi SCC VII tCSC had significantly elevated PD-L1 expression compared with CD44lo cells in the absence or presence of strong Th1 inflammation following delivery of 50 μg polyinosinic-polycytidylic acid (polyI:C), a synthetic Toll-like receptor 3 (TLR3) ligand (Supplemental Figure 3E) (11). Here, CD274 is linked to head and neck squamous cell carcinoma.