Allogeneic stem cell transplantation is the treatment of choice for many patients with leukemia and other hematologic malignancies. However, a major limitation of this therapy is that for a significant number of patients no fully HLA-matched donor can be found. The application of partially HLA-matched (haploidentical) family donors, who are virtually always available, has some complications. If there is no T-cell add-back it increases the risk for life-threatening infections and disease relapse, while in case of T-cell add-back the risk for graft-versus-host disease is raised.