In vitro differentiation of human NK cells from NOD/SCID BM and spleen and from human CB. (A) Single-cell suspensions of BM (I: n = 13, □) and spleen (II: n = 5, ▧) of NOD/SCID that underwent transplantation and purified CB CD34⁺ cells (III: n = 7, ▪) were cultured for 4 weeks in NK differentiation medium containing recombinant human IL-15, FL, and SCF. The appearance of CD56⁺ NK cells was determined by FACS analysis. Shown are the mean ± SEM percentages of total cells in the cultures. nd indicates not determined. (B) Expression of CD16 and CD56 and of (C) NKp46 on CD56⁺ NK cells generated in cultures I, II, and III at 4 weeks. Thin line indicates staining with isotype-matched control antibody. Numbers indicate the percentages of NKp46⁺ NK cells.