Non–FcγR-binding anti-CD3 mAbs hOKT3γ1[Ala/Ala]/teplizumab and foralumab are antileukemic in T-ALL. (A) NSG mice infused with 10⁶ pCCL-c-MNDU3c-Luc-muPGK-eGFP–transduced leukemic cells from T-ALL UPNT-420 were monitored for luciferase activity. Once leukemic (27 days postinjection), mice (n = 3 per group) were treated with 4 µg per day of control mIgG2a, OKT3, hOKT3γ1[Ala/Ala], or foralumab for 4 consecutive days, as indicated, and followed over time. Left panel, bioluminescence at day 37. Right panel, bioluminescence quantification over time. (B) Leukemia burden in peripheral blood of NSG mice injected with the indicated human T-ALL primary PDX. At high leukemia burden, mice were treated with either 4 μg per day of control hIgG1 (n = 4), OKT3 (n = 4), or hOKT3γ1[Ala/Ala] (n = 4) for 5 consecutive days. Data show tumor burden in peripheral blood at the time point when control mAb–treated mice reached maximal, tolerable leukemia invasion. (C) Leukemia burden in blood of mice injected with T-ALL M106, UPNT-760, and UPNT-584, treated as in panel B, and followed over time. Dashed lines indicate period of treatment. (D) Kaplan-Meier survival curves of NSG mice receiving transplants of T-ALL M106, UPNT-760, and UPNT-584 and treated as in panel B. **P < .01, ***P < .001.