CD274 and head and neck squamous cell carcinoma: This interesting finding has also been confirmed by the observation of increased PD-L1 expression in mouse HNSCC of Pten conditional knockout (Pten cKO) mice, Tgfbr1 conditional knockout (Tgfbr1 cKO) mice and Pten/Tgfbr1 2cKO mice (Fig. 2E).