Blinatumomab (MT103) is a bispecific antibody derivative, anti-CD19 x anti-CD3, designed to link B-cells and T-cells resulting in T-cell activation and a cytotoxic T-cell response against CD19+ cells. Data of prior phase I studies show evidence of biological activity in humans. In vitro and ex-vivo data suggest that a longterm presence of the drug in target tissues may provide antitumour activity.