The overall purpose of the study is to determine if MEDI-551, when used in combination with salvage chemotherapy, Ifosfamide-carboplatin-etoposide (ICE) or Dexamethasone-cytarabine (DHAP) in patients with relapsed or refractory DLBCL who are eligible for Autologous Stem Cell Transplant (ASCT), has superior efficacy compared to rituximab in the same population.