LUSV is effective in overt leukemia PDX models. (A-C) A phase 2-like PDX study was performed using 24 PDX samples of patients with BCP-ALL and T-ALL with different CD127 expression levels including 8 samples from relapsed/refractory (R/R) disease. Two NSG mice per patient were injected with PDX cells, randomly assigned into treatment groups, and LUSV therapy was initiated upon detection of 1% PDX cells in the PB, modeling an overt leukemia situation. (A) Blood of both control and LUSV-treated animals bearing the same PDX sample was withdrawn when 1 of the 2 PDX mice showed signs of overt leukemia, and the number of hCD45⁺/hCD19⁺/mCD45^– cells in the PB was measured via flow cytometry. The waterfall plot shows the difference in PBBs between respective control and LUSV-treated mice (ΔPBB, sorted from weakest therapy response to highest therapy response). Animals not showing clinical signs of overt leukemia or >70% PBBs at this time point received further treatment until reaching termination criteria. The dotted line indicates a ΔPBB of 50%. The white asterisk indicates matched samples obtained from initial diagnosis and relapse from the same patient. (B) Therapy-associated differences in the survival of NSG mice were determined using Kaplan-Meier log-rank statistics. The experiment was terminated after 280 days, and 1 LUSV–treated PDX animal was found free of leukemia. (C) The in vivo response to LUSV therapy as depicted via the ΔPBB value was correlated with the ratio of CD127⁺ cells in corresponding PDX samples determined via flow cytometry, Pearson linear regression, confidence interval (0.4010-0.8565). ∗P < .05; ∗∗P < .01; ∗∗∗P < .001; ∗∗∗∗P < .0001.