IL15 and cancer: Cells used as feeder layers have included cancer cells [51] such as the Jurkat subline KL-1 [52], genetically modified K562 cells engineered to express membrane-bound IL-15 and IL-21 fused to 4-1BB [53, 54], Epstein-Barr virus-transformed lymphoblastoid cells [55], or irradiated peripheral blood mononuclear cells in the presence of anti-CD16 antibody [56].