Correlation between the percentages of CD34⁺ cells expressing CXCR-4 and the outgrowth in NOD/SCID. Samples from 21 AML patients were injected in NOD/SCID mice (3 × 10⁷ cells per mouse, 3-5 mice per group). After 6 weeks the mice were killed and the number of human AML cells in the bone marrow was determined by flow cytometry. The outgrowth of AML cells in NOD/SCID was then correlated with the percentages of CD34⁺ cells expressing CXCR-4.