The main purpose of this project is to cure patients with high risk Sickle cell disease and other red cell disorders including thalassemia and diamond-blackfan anemia by bone marrow transplantation. The patients enrolled in this study will be those who lack matched sibling donors and therefore have no other option but to undergo bone marrow transplantation using matched but unrelated bone marrow or umbilical cord blood from the national marrow donor program registry. Since bone marrow transplantation for these disorders using matched unrelated donors has two major problems i.e. engraftment, or , the process of new marrow being accepted and allowed to grow in the the patient; and graft-versus-host disease, or the process where the new marrow "rejects" the host or the patient, this study has been devised with methods to overcome these two problems and thus make transplantation from unrelated donors both successful in terms of engraftment and safe in terms of side effects, both acute and long term.