The T-cell–engaging anti-CD3 BsAb induces potent T-cell fratricide in vitro. Activated T cells were expanded for 9 days and cultured with 350 pM of the Ab in the presence of IL-2 (30 IU/mL). The number of live CD4 (A) and CD8 cells (B) was calculated using CountBright Absolute Counting Beads (Invitrogen). Dead cells were excluded using annexin-V staining. Area under the curve was compared between groups using analysis of variance (ANOVA) and multiple comparison analysis. n = 3 technical replicates per time point per condition. Experiment was repeated 3 times.