Furthermore, in vitro culture protocols for expanding high yields of primary human NK cells utilize allogeneic tumor cell lines such as K562 cells expressing ligands for the NK cell receptors NKp30, 41BB and IL-21R as feeder cells in combination with IL-2/IL-15-containing media, and the combination of these signals is required for optimal NK cell expansion [40]. This evidence concerns the gene NCR3 and neoplasm.