CD19 and neoplasm: CD107a expression was observed in CAR T‐19, DKO‐CAR T‐19, DKO‐CAR T‐19mBE, and DKO‐CAR T‐19mBG cells after coincubation with the CD19+ cell line Raji (Fig. 3F and Supporting Information Fig. 4), indicating that these cells had specific cytolytic activity against CD19‐positive tumor cells.