Effective Treatment of Relapsed/refractory CD19-positive B/T-type Mixed-phenotype Acute Leukemia with Blinatumomab: A Case Report

A 26-year-old man was diagnosed with B/T-type mixed-phenotype acute leukemia (MPAL-B/T) based on blasts being positive for CD19, cytoplasmic CD3, and cyCD79a, but negative for myeloperoxidase. Acute lymphoblastic leukemia-based chemotherapy was started, but the leukemia was refractory. He underwent cord blood transplantation with the conditioning regimen of total body irradiation plus cyclophosphamide and cytarabine with granulocyte-colony stimulating factor priming. Prophylaxis for graft versus host disease was performed with short-term methotrexate and cyclosporin. The leukemia relapsed in bone marrow 20 months later. At that time, he was treated with inotuzumab ozogamicin because the blasts expressed CD22 (75.4%), but this was ineffective. He was next administered blinatumomab with dexamethasone pretreatment, resulting in a complete remission (CR). He subsequently underwent human leukocyte antigen-haploidentical peripheral blood stem cell transplantation. He has still maintained a CR for 12 months. Blinatumomab might be a promising treatment and a bridge to stem cell transplantation even in relapsed/refractory CD19-expressing MPAL-B/T.