PTL improves the survival of NSG mice engrafted with ALL subpopulations. (A) NSG mice were transplanted with bulk and sorted subpopulations from B-ALL and T-ALL patients. Once engrafted, mice were treated for 9 days with PTL (40 mg/kg/d) and monitored thereafter. (B-C) Kaplan-Meier plots of the survival of mice engrafted with B-ALL (B, patients 6, 20, 22, 27, and 28) and T-ALL subpopulations (C, patients 30, 32, 34, and 35). The time indicated is time from commencement of treatment (day 0). The numbers in parentheses signify the numbers of mice used in each group. (D-E) PTL decreases leukemia cell burden in xenografts from B-ALL populations (D) and T-ALL populations (E). The percentage of leukemia cells in the BM of individual mice from each inoculated population is shown. Each symbol represents a specific patient. **P ≤ .01 and ***P ≤ .001 compared with untreated mice. (F) Flow cytometric analysis of BM from mice engrafted with CD34⁺/CD19⁻ cells from patient 20. Results from an untreated and a treated mouse are shown. In histograms, gray peaks represent murine CD45 and black peaks are isotype controls. Spleens removed from the treated mouse (PTL, left) and untreated mouse (U, right).