Figure 1.

NK cells reduce HSC maintenance and function in culture

(A) Graphical representation of the experimental design. Co-cultures were established in stem cell medium containing stem cell factor (SCF), Flt3-ligand, IL-3, IL-6, thrombopoietin (TPO), and IL-2 over an OP9 stromal cell layer using sorted BM CD45.2⁺ HSCs (lin⁻ c-Kit⁺ Sca-1⁻ CD48⁻ CD150⁺) and SP CD45.1⁺ NK cells (Ter119⁻ CD19⁻ CD4⁻ CD8⁻ CD3⁻ NK1.1⁺). Days of culture are indicated. HSCs were enumerated by FACS analysis.

(B) Quantification of HSCs recovered from 4-day cultures by FACS analysis. Y axis indicates the absolute number of HSCs. X axis indicates presence (+) or absence (−) of NK cells in culture (ratios are indicated). Values and error bars indicate medians ±SEM. n = 3 biological samples in each condition. Jonckheere-Terpstra trend test was used to assess statistical significance (p value is indicated).

(C) Experimental design of in vitro colony culture assays.

(D) Quantification of colonies at day 10 of culture. Y axis indicates the number of CFU relative to the HSC counts. X axis indicates cells present in the semi-solid cultures. Two different HSC/NK cell ratios were used as indicated. Data indicate mean ± SD of three independent biological triplicates. Each dot represents one culture well. Two-tailed Student's t test was used to assess statistical significance (p values are indicated).