 This is a pilot study of a novel HSCT protocol for patients with high-grade andor recurrent neuro-epithelial and other solid tumors. To determine the feasibility of allogeneic HSCT following thiotepa-based marrow ablative chemotherapy MAC for children with high-grade andor recurrent neuro-epithelial and other solid tumors. The primary end-point for this study is to determine progression-free survival PFS at six months post-HSCT. Secondary end-points include: a overall survival OS at one year b transplant related mortality TRM at Day 100 c engraftment d regimen related toxicity: the frequency and severity of acute and chronic graft-versus-host disease GVHD, sinusoidal obstructive syndrome and infections will be assessed e time to immune reconstitution following HSCT. Exploratory Aims include: 1 To assess the feasibility of the Taqman Low Density Arrays TLDA assay as a technology for MRD detection among a subset of patients with high-grade andor recurrent neuro-epithelial and other solid tumors. Minimal residual disease MRD when applicable in bone marrow pre- and post-HSCT, will be assessed using TLDA. Currently, for solid malignancies there is no routinely established method to detect minimal residual disease, the first indicator of therapy failure andor recurrence of disease. 2 In an effort to minimize morbidity related to graft-versus-host disease, alemtuzumab forms an important component of the proposed MAC regimen for recipients of unrelated or related mismatched allogeneic grafts. As an exploratory aim, an alemtuzumab assay will be performed at specified intervals to explore time to drug clearance. This may provide important information regarding lymphodepletion for future trials regarding immunotherapy administered during recovery from HSCT therapy. 