Hematopoietic progenitor cell-derived NK cells express less KIR in the presence of CSA. Umbilical cord blood (UCB)–derived CD34⁺CD38⁻Lin⁻ cells cultured on a stromal cell line (AFT024) in the presence of cytokines (IL-3, IL-7, IL-15, SCF, and FLT-3L) and increasing amounts of CSA (0.1-5 μg/mL) as described in “NK-cell differentiation cultures, Materials and methods.” On day + 50, cultures were examined for (A) total cell number, (B) percentage, and (C) absolute number of KIR-expressing NK cells. Results are the average of cells from 4 donors plus and minus the SEM. Asterisk (*) indicates values that were significantly less than controls (P < .05) by Mann-Whitney rank sum test