Immunophenotypic features of NK cells before and after expansion with K562-mb15-41BBL cells. Expression of CD3 and CD56, as well as expression of the KIRs CD158a (2DL1), CD158b (2DL2), NKB1 (3DL1), and NKAT2 (2DL3) on CD56⁺CD3^- cells were examined in peripheral blood mononuclear cells from a healthy donor before (top row) and after (bottom row) 3 weeks of coculture with K562-mb15-41BBL cells and low-dose (10 U/mL) IL-2.