RAET1E and nasopharyngeal carcinoma: To further verify the impact of ULBP4 expression on the cytotoxicity activity of immune cells in vitro, our LDH cytotoxicity analysis demonstrated considerably increased the cytotoxic activity of NK cells against NPC cell lines (C666-1 or 5-8F) with lenti-ULBP4 as compared to those with lenti-vector at the three E/T ratios (10:1, 20:1, and 40:1), respectively (Figure 4).