The detection of minimal residual disease (MRD) after induction therapy and/or consolidation therapy is an independent prognostic factor for poor outcome of adult ALL. No standard treatments are available for patients with MRD-positive B-precursor ALL. Blinatumomab (MT103) is a bispecific single-chain antibody construct designed to link B cells and T cells resulting in T-cell activation and a cytotoxic T-cell response against CD19 expressing cells. The purpose of this study is to confirm whether the bispecific T-cell engager blinatumomab (MT103) is effective, safe and tolerable in the treatment of ALL patients with minimal residual disease.