CD274 and nasopharyngeal carcinoma: To determine the expression of PD-L1 in NPC, we performed real time PCR and western blot to detect mRNA level and protein level of several common human NPC cell lines (EBV-negative: CNE-1, CNE-2, SUNE-1, 5-8F, 6-10B, TWO3 and HNE-1; EBV-positive: C666-1) and in an immortalized nasopharyngeal epithelial cell line (NP-69).