Reduced Intensity Conditioning for Umbilical Cord Blood Transplant in Pediatric Patients With Non-Malignant Disorders

Myeloablative doses of chemotherapy and/or radiation therapy are employed with the primary purpose of eradicating malignant cells. Additionally, these regimens exert varying degree of immunosuppression/immunoablation that aids in reducing the likelihood of rejection by host hematopoietic cells. However, myeloablative /immunoablative regimens have also been associated with significant regimen related toxicity (RRT) and regimen related mortality (RRM) that may cause death in up to 20% of patients and significantly higher rate of severe organ dysfunction or failure. While most of these RRT occur typically in the first 100 days \[ e.g. VOD (veno occlusive disease), pulmonary or intracranial hemorrhage, multiorgan failure (MOF)\], there are significant long term toxicities of TBI and/or chemotherapy including growth impairment, gonadal dysfunction/failure, hypothyroidism, cataracts, neurocognitive impairment, and second malignancies. The primary objective is to determine the feasibility of attaining acceptable rates of donor cell engraftment (\>25% donor chimerism at 180 days) following reduced intensity conditioning (RIC) regimens in pediatric patients \< 21 years receiving cord blood transplantation for non-malignant disorders. The secondary objectives are: * To describe the pace of neutrophil and platelet recovery * To evaluate the pace of immune reconstitution. * To determine the treatment related mortality, overall survival and disease free survival by days 100 and 180 post-transplant * To describe incidence of acute Graft Versus Host Disease (GVHD) (II - IV) and chronic extensive GVHD * To describe the incidence of grade 3-4 organ toxicity * To evaluate long-term complications, such as sterility, endocrinopathy, and growth failure * To evaluate the incidence of late graft failures at 2 years post-transplant