 This is a Phase 2 study designed to assess safety, feasibility and clinical activity of pre-HCT moxetumomab pasudotox for patients with ALL in morphologic CR but with MRD. It is hypothesized that subjects in a morphologic complete remission with proven minimal residual disease MRD after chemotherapy for ALL planned for allogeneic HCT who receive a course of moxetumomab pasudotox prior to the start of conditioning will show a marked reduction or elimination of detectable MRD after moxetumomab pasudotox treatment without adverse impact on the feasibility or safety of allogeneic HCT. 