Humanized VH4vκ1 exhibited efficient antitumor activity against CD19-low tumor in vivo. (A) Schema showing NSG mice engrafted IV with eGFP⁺ ffluc⁺ Raji CD19-low cells followed by murine and humanized CAR T cell treatments. Mock was used as the control group for FMC63 and humanized VH4vκ1- and 4D5-treated groups. (B-D) Representative figure of tumor progression in different groups is shown over time. Tumor progression was monitored using BLI (5-9 technical replicates per group) and log-transformed flux is shown for each treatment over time. Tumor progression was effectively controlled by FMC63 and VH4vκ1 compared with 4D5 (day 6, 13, and 20: P < .001 FMC63 vs 4D5; and P < .001 VH4vκ1 vs 4D5). (D) Survival of mice treated with murine FMC63 compared with the 2 humanized CARs was analyzed using the log-rank test: ∗∗∗P < .001 (n = 5-9 mice per group). Representative data from 2 separate experiments are presented. (E) Percent of CAR T cells in mice blood was analyzed at the end of the experiment (P < .01, untransduced T cells [Mock] vs FMC63, VH4vκ1, and 4D5).