Transplantation for Patients With Sickle Cell Disease From Mismatched Family Donors of Bone Marrow

Inclusion Criteria: 1. Disease severity: Participants with SCD who have 1 or more of the following (i-v). * Clinically significant neurologic event (stroke) or any neurological deficit lasting \> 24 hours; * History of two or more episodes of acute chest syndrome (ACS) in the 2-year period preceding enrollment despite the institution of supportive care measures (i.e. asthma therapy and/or hydroxyurea); * History of three or more severe pain crises per year in the 2-year period preceding enrollment despite the institution of supportive care measures (i.e. a pain management plan and/or treatment with hydroxyurea); * Administration of regular red blood cell (RBC) transfusion therapy, defined as receiving 8 or more transfusions per year for ≥ 1 year to prevent vaso-occlusive clinical complications (i.e. pain, stroke, and ACS). Patients on chronic transfusion who have to discontinue transfusion because of allo-sensitization will be eligible. * An echocardiographic finding of tricuspid valve regurgitant jet (TRJ) velocity ≥ 2.7 m/sec. Patients under the age of 18 years must have cardiac catheterization proven pulmonary arterial hypertension to qualify on this eligibility criterion. 2. Age: Patients must be 15 - 40 years of age inclusive OR if younger than 15 years must be pubertal 3. Adequate physical function as measured by: * Karnofsky/Lansky performance score ≥ 60 * Cardiac function: Left ventricular ejection fraction (LVEF) \> 40% or LV shortening fraction \> 26% by cardiac echocardiogram or by MUGA scan. * Pulmonary function: Pulse oximetry with a baseline O2 saturation of ≥ 85% and DLCO \> 40% (corrected for hemoglobin). * Renal function: Serum creatinine ≤ 1.5 x the upper limit of normal for age as per local laboratory and 24 hour urine creatinine clearance \> 70 mL/min/1.73 m2 or GFR \> 70 mL/min/1.73 m2 by radionuclide GFR. * Hepatic function: Serum conjugated (direct) bilirubin \< 2 x upper limit of normal for age as per local laboratory and ALT and AST \< 5 x upper limit of normal as per local laboratory. Patients with hyperbilirubinemia as a consequence of hyperhemolysis, or who experience a sudden, profound change in the serum hemoglobin after a RBC transfusion, are not excluded. * For participants with a suitable donor who meet eligibility criteria and are willing to proceed to HCT, if they have received chronic transfusion therapy for ≥ 1 year and have clinical evidence of iron overload by serum ferritin or MRI, an evaluation by liver biopsy is required. Histological examination of the liver must document the absence of cirrhosis, bridging fibrosis, and active hepatitis. The absence of bridging fibrosis will be determined using the histological grading and staging scale 4. Suitable Donor: To undergo transplantation on this study, participants must have an adult first degree relative who shares at least 1 human leukocyte antigen (HLA) haplotype with the participant, does not have SCD or other hemoglobinopathy, and is in good health; if these criteria are met, they will be allowed to serve as donors. Relatives with sickle cell trait are not excluded as donors. When more than 1 donor is available, the donor with the fewest HLA allele mismatches will be chosen, unless the patient had donor anti-HLA antibodies or there was a medical reason to exclude the donor. If donor anti-HLA antibodies are detected, the next best related match will be chosen. Umbilical cord blood or peripheral blood stem cell donors will not be accepted. Exclusion Criteria: * Availability of HLA matched sibling or 8 of 8 HLA-A, B, C and DRB1 matched unrelated donor * Presence of donor specific antibodies in the patient * Histological examination of the liver must document the absence of cirrhosis, bridging fibrosis and active hepatitis. The absence of bridging fibrosis will be determined using the histological grading and staging scale as described by Ishak and colleagues (1995). The presence of bridging fibrosis will be an exclusion criterion. * Uncontrolled bacterial, viral or fungal infection in the 6 weeks before enrollment * Seropositivity for HIV * Previous hematopoietic cell transplantation (HCT) * Participation in a clinical trial in which the patient received an investigational drug or device or off-label use of a drug or device within 3 months of enrollment * Demonstrated lack of compliance with prior medical care * Unwilling to use approved contraception for at least 6 months after transplant * A history of substance abuse in the last 5 years that interferes with care * Pregnant or breast-feeding females at the time of consideration for HCT Donor Selection Criteria: Preference will be given to related marrow donors who are 2-4 (out of 8) HLA antigen mismatched and towards whom the recipient does not have donor specific antibodies. Donors will sign an informed consent disclosing that the marrow donation will be used by a patient participating in this study. The donor must be matched with the recipient for at least 4 of 8 HLA alleles (HLA -A, -B, -C and -DRB1 by allele-level DNA methodology). The target total nucleated cell count (TNC) is 3.5-8.0 x 108/kg of recipient weight. Marrow will be collected without mobilization. Mobilized peripheral blood stem cell (HPC-A) collections will not be permitted. Donors must undergo hemoglobinopathy screening by electrophoresis; donors who have a hemoglobinopathy will be excluded but trait condition is acceptable.