Anti-CAR19 CART cells deplete CAR19⁺ T cells. (A) Model: anti-CAR19 CART (αCAR19-CART) can recognize CAR19-expressing T cells and trigger cytotoxicity. (B) αCAR19-CART H-L (left) or L-H (right) (effectors) were cocultured with control T cells, CART19, or CART22 cells (targets, CellTracker Orange [CTV-positive]) and the percentage of surviving target cells was measured at 48 hours using flow cytometry. CART19 cells were specifically killed by αCAR19-CART. (C) αCAR19-CART H-L (left) or L-H (right) (effectors, carboxyfluorescein succinimidyl ester–positive) were cocultured with control T cells, CART19, or CART22 cells (targets, CTV-positive) at different effector-to-target (E:T) ratios, and changes on the E:T ratios were recorded at 48 hours. For E:T ratios >2, αCAR19-CART killing prevails over CART19. A total of 100 000 events were acquired for each condition. All experiments were repeated twice. Asterisks are used in each figure to represent P values (*P < .05, **P < .01).