Only CD200⁺ cells can engraft NSG mice in low-risk ALL. Cells from MRD low-risk patients 14, 23, 25, 26, and 30 and risk patients 22, 24, and 27-29 were sorted for expression of CD34 and CD200. Unsorted cells and the sorted subfractions were evaluated for their ability to engraft primary (A) and secondary (B) NSG mouse recipients. Each patient is represented by a specific symbol, and each symbol depicts the engraftment as measured by human cells present in the BM of the NSG mice .