IL-1RA inhibits growth of human CML stem cells in combination with NIL. Primary human CML and normal CD34⁺CD38⁻ primitive stem/progenitor cells were cultured in human CML BM CM and exposed to NIL (5 μM), IL-1RA (5 μg/mL), NIL⁺IL-1RA, or vehicle for 72 hours. Cell growth (A), cell proliferation (B), CFC (C), and apoptosis (D) are shown. A representative flow cytometry plot showing CFSE and Annexin V labeling is shown (E). CD34⁺ cells treated with NIL, IL-1RA, and NIL⁺IL-1RA were plated in CFC assays (left), and after 14 days colonies were harvested and cells resuspended and replated in secondary CFC assays (right) (F). CML CD34⁺ cells treated with IL-1RA, NIL, or IL-1RA in combination with NIL for 72 hours were transplanted into irradiated (300 cGy) NSG mice (n = 6 each). Engraftment of human CD45⁺ cells in the BM of NSG mice at 4 weeks (G) and 16 weeks (H) is shown. BCR/ABL expression in the enriched human CD45⁺ cells in the BM at 16 weeks was measured (I). Results represent mean ± SEM. Significance values: *P < .05; **P < .01; ***P < .001, 2-way ANOVA, 1-way ANOVA. FITC-A, fluorescein isothiocyanate-A; PE-A, phycoerythrin.