CD13⁺CD56⁻cells can give rise to NK cells. (A) Cells with distinct levels of CD13 expression: CD13^low/neg (bottom), CD13^intermediate (middle), and CD13^high (top) were FACS purified from NK differentiation cultures (at day 14) and cultured further with cytokines and stroma. All 3 subsets gave rise to CD56⁺ NK cells, some of which coexpressed CD13. (B) Quantitative yield of CD56⁺ NK cells/10⁴ CD13⁺ cells undergoing FACS. There was decreasing ability for NK-cell generation with increasing CD13 expression. A representative donor is shown (n = 4). Groups showing significant differences are indicated by asterisks (***P < .001, **P = .001-.01, and *P = .01-.05), 1-way analysis of variance on log-transformed values with Bonferroni posttest. (C) Freshly isolated GMPs (CD34⁺CD38⁺CD123⁺CD45RA⁻) were double-sorted from UCB and deposited into 96-well plates with stroma, HDC, and cytokines (FLT-3L, SCF, IL-7, and IL-15). After ∼ 21 days progeny were analyzed by FACS. Shown are the cells falling within the lymphoid gate by FSC versus SSC.