PDCD1 and head and neck squamous cell carcinoma: Furthermore, TIMER2 database was used to examine the correlation between the expression of the major immune checkpoint genes and ZC3H12D expression, including SIGLEC15, TIGIT, HAVCR2, CTLA4, PDCD1, PDCD1LG2, CD274, and LAG3. Supplementary Figure S4A and B showed that the expression of the above immune checkpoint genes was strongly positively correlated with ZC3H12D expression in HNSCC.