The aim of the study is to investigate the feasibility and toxicity of allogeneic haploidentical or unrelated transplantation with CD3/CD19 depleted stem cells associated with a reduced or a standard conditioning regimen in pediatric patients with malignant and non-malignant high-risk diseases, for whom allogeneic stem cell transplantation represents the only possible therapy option and no human leukocyte antigen (HLA) compatible related donors are available.