Coordinated acquisition of inhibitory and activating receptors and functional properties by developing human natural killer cells

The stages of human natural killer (NK) cell differentiation are not well established. Culturing CD34⁺ progenitors with interleukin 7 (IL-7), IL-15, stem cell factor (SCF), FLT-3L, and murine fetal liver cell line (EL08.1D2), we identified 2 nonoverlapping subsets of differentiating CD56 ⁺ cells based on CD117 and CD94 (CD117^highCD94^- and CD117^low/-CD94⁺ cells). Both populations expressed CD161 and NKp44, but differed with respect to NKp30, NKp46, NKG2A, NKG2C, NKG2D, CD8, CD16, and KIR. Only the CD117^low/- CD94⁺ population displayed cytotoxicity and interferon-γ production. Both populations arose from a single CD34⁺CD38^- Lin^- cell and their percentages changed over time in a reciprocal fashion, with CD117 ^highCD94⁺cells predominating early and decreasing due to an increase of the CD117^low/-CD94⁺ population. These 2 subsets represent distinct stages of NK-cell differentiation, since purified CD117^high CD94^- cells give rise to CD117 ^low/-CD94⁺ cells. The stromal cell line (EL08.1D2) facilitated the transition from CD117^highCD94^- to CD117^low/-CD94⁺ via an intermediate phenotype (CD117 ^lowCD94^low/-). EL08.1D2 also maintained the mature phenotype, preventing the reversion of CD117^low/-CD94⁺ cells to the intermediate (CD117^lowCD94^low/-) phenotype. An analogous population of CD56⁺CD117^highCD94^- cells was found in cord blood. The identified stages of NK-cell differentiation provide evidence for coordinated acquisition of HLA-specific inhibitory receptors (ie, CD94/NKG2A) and function in developing human NK cells.