Long-term AML1-ETO-expressing cultures engraft NOD/SCID mice. (A-B) Stem cell engraftment. NOD/SCID mice were injected intravenously with different long-term AML1-ETO-expressing cell cultures and with control CB CD34⁺ cells. After 6 to 8 weeks, mice were killed and bone marrow cells were collected from both femurs and both tibias. Samples were analyzed for the presence of human cells using an antihuman CD45-PE antibody by flow cytometry. Genomic DNA was collected from the remaining cells and real-time quantitative PCR was performed using primers for the human endogenous retrovirus (HERV) and GAPDH as the quantitative control primer set. All samples in panel B are from mice injected with long-term AML1-ETO-expressing cultures. Based on standard curves using DNA from human-murine cell mixtures, a relative level of 1 corresponds to a 0.001% human population. Shown are the average and SD of triplicate reactions.