CD19 and leukemia: In patient 5, circulating leukemia cells were present on day 1, and dramatic CAR T cell expansion was observed on day 14, consistent with the elimination of normal B cells and malignant blasts, followed by the disappearance of CD19/CD22 CAR T cells by day 100 with the reconstitution of normal B cells but continued absence of blasts (Fig. 3c).