INTRODUCTIONThe prognosis of adult relapse or refractory B cell acute lymphoblastic leukemia (r/r B-ALL) is dismal, with a complete remission rate of approximately 18%-44% if receiving salvage chemotherapy[1]. In recent years, immunotherapy represented by blinatumomab, inotuzumab ozogamicin (InO) and chimeric antigen T-cell (CART) therapy has demonstrated profound efficacy in r/r B-ALL[3-5]. However, those who have persistent positive measurable residual disease (MRD) still remain a high risk of relapse and poor outcome [2]. So far, only blinatumomab is approved for the treatment of MRD in B-ALL[4]. CD22 is detected to be expressed in more than 90% of B-ALL patients, indicating that CD22 is an ideal therapeutic target for B-ALL [6]. InO is an antibody-drug conjugate comprising a humanized anti-CD22 monoclonal antibody conjugate to calicheamicin. According to the INO-VATE study, significantly higher rate of complete remission was observed in r/r B-ALL patients who received InO monotherapy compared with traditional chemotherapy (73.8% vs 30.9%, P <0.0001) This encouranging data lead to the approvment of InO for the treatment of r/r B-ALL by the US Food and Drug Administration in 2017 [3]. Hitherto, the application of InO in the treatment of MRD has not been reported.