SIGLEC15 and head and neck squamous cell carcinoma: Similarly, we investigated the relationship between CELSR3 and immunoassays, as well as the expression of immune checkpoints, such as CD274, CTLA4, HAVCR2, LAG3, PDCD1, PDCD1LG2, TIGIT, and SIGLEC15 (Figs. 5A), in WHO grade I and II HNSCC.