PROM1 and neoplasm: CD133+SW620 (moderate expression of surface ULBP3), CD133−SW620 (high expression of surface ULBP3), and CD133−SW620ULBP3-siRNA (no/low expression of surface ULBP3; Figure 3A) tumor cells were used as target cells, and NK cells were freshly isolated from healthy volunteers for use as effector cells in cytotoxicity assays.