Graft-versus-host disease (GVHD) is a condition that results from a reaction of transplanted donor T-lymphocytes against the body and organs of the patient receiving the transplanted cells. There are two forms: acute (early) and chronic (late). Acute GVHD may produce skin rashes, liver disease, diarrhea, and an increased risk of infection. Chronic GVHD can appear in patients without prior acute GVHD. Chronic GVHD may also produce skin rashes, liver disease, diarrhea and an increased risk of infection. GVHD can make patients very sick, and have GVHD can make it more likely that patients will not survive their transplant. In this study, the investigators are offering to treat the donor peripheral blood stem cells in the hope that it will make it less likely for the patient who receives them from having GVHD.

Patients on this study are being offered an experimental treatment involving the use of the CliniMACS® Reagent System (Miltenyi Biotec, Germany), a CD34+ selection device to remove T-cells from the peripheral blood stem cell transplant in order to decrease the risk of acute and chronic GVHD. CD34+ stem cells are selected from the donor's peripheral blood stem cells. In doing this, T-cells are also removed. T-cells are the cells which are responsible for graft versus host disease (GVHD). This study is a clinical trial for patients diagnosed with a non-malignant disease who will receive a peripheral blood stem cell transplant. Patients with the following types of non-malignant diseases can participate in this study: Bone marrow failure syndromes (including Severe Aplastic Anemia, Severe Congenital Neutropenia, Amegakaryocytic Thrombocytopenia (Kostmann's Syndrome), Diamond-Blackfan Anemia, Schwachman Diamond Syndrome, Primary Immunodeficiency Syndromes, Acquired Immunodeficiency Syndromes, and Histiocytic Disorders) and Hemoglobinopathies (including Sickle Cell Anemia and Sickle/Beta Thalassemia). Patients on this study will be given standard transplant therapy with either high doses of chemotherapy drugs or lower doses of chemotherapy drugs, depending on their disease. Diseases within each disease group will receive chemotherapy that is standard for that condition.

Some patients on this study will receive an allogeneic stem cell transplant (AlloSCT) from a matched related donor. If a patient does not have a matched related donor, a bone marrow search will be done at all of the bone marrow banks in the world. The patient will then go on to receive an AlloSCT from either a partially matched family member or an unrelated adult stem cell transplant donor. The transplanted cells will allow all the normal parts of the patient's blood system to recover. The experimental portion of this treatment involves the use of a Miltenyi CliniMACS CD34+ selection device to remove T-cells from the peripheral blood stem cell transplant in order to decrease the risk of acute and chronic GVHD. CD34+ stem cell selection AlloSCT has been studied in adults with the malignant and non-malignant disease with successful engraftment and has shown some improvement in GVHD. It is unknown if CD34+ stem cell selection will work to prevent severe GVHD in children and adolescents.