Unrelated Hematopoietic Stem Cell Transplantation(HSCT) for Genetic Diseases of Blood Cells

This is a pilot clinical trial of hematopoietic stem cell transplantation for patients with the diagnosis of a genetic disease of blood cells that do not have an HLA-matched sibling donor. The stem cells will be derived from a 1) matched unrelated donor (MUD) or 2) unrelated umbilical cord blood (UCB). Patients will receive a novel conditioning regimen with Busulfan, Cytoxan and Fludarabine (Bu/Cy/Flu) and either Alemtuzumab (Campath 1H) for recipients of a MUD or rabbit Antithymocyte Globulin (rATG) for recipients of unrelated UCB prior to hematopoietic stem cell transplant (HSCT). It is hypothesized that reduced dosages of Cytoxan will decrease the acute toxicities associated with the standard chemotherapies of Busulfan and Cytoxan (i.e. sinusoidal obstructive syndrome (SOS), hemorrhagic cystitis and mucositis). And the addition of fludarabine to a conditioning regimen with myeloablative doses of Busulfan and reduced dosages of Cytoxan prior to HSCT will overcome the engraftment barrier posed by an intact immune system, which is seen in patients with a genetic disease.