The present study also suggests that TGFBR1 loss further enhances the expression of PD-L1 in HNSCC cell lines and conditional Tgfbr1−/− mice, which indicate that loss of TGFBR1 may be an crucial molecular event leading to the accumulation of PD-L1 in both HPV infection and alcohol or tobacco use [18, 30]. This evidence concerns the gene CD274 and head and neck squamous cell carcinoma.