Despite an improved understanding of disease biology and the use of multi-agent chemotherapy, the long-term survival of adults with B-cell acute lymphoblastic leukemia (B-ALL) ranges from 35% to 50%. Management of patients with relapsed B-ALL, a group characterized by dismal outcomes, poses a clinical challenge. To address this unmet need, novel therapeutics are being investigated in the setting of relapsed B-ALL with encouraging results. CD22 is an important B-cell antigen expressed in 80-90% of B-ALL cases. CD22 undergoes constitutive endocytosis with antibody ligation, making it an attractive biologic target for immunoconjugates. Inotuzumab ozogamicin (IO), a CD22-targeted antibody-drug conjugate demonstrated impressive single agent activity even among heavily pretreated relapsed B-ALL patients. A recent randomized phase III clinical trial demonstrates superiority of IO over standard of care chemotherapy as first- or second-line salvage therapy for relapsed B-ALL. In this review, we summarize the preclinical and clinical data available to date using IO in relapsed B-ALL.