CD19 and leukemia: Both untreated mice and tEGFR-CAR-treated mice rapidly experienced a leukemia event (defined as >20% total nucleated cells in peripheral blood expressing human CD19) at a median of 35 and 55 days, respectively, while median event-free survival was not reached in mice treated with either SPB CAR19 or PBat CAR19 (Figure 7B; p < 0.01).