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

Participants will receive a bone marrow infusion from a human leukocyte antigen (HLA) mismatched donor through a central venous catheter.

Hydroxyurea is part of the bone marrow transplant preparative regimen. Hydroxyurea will be administered at a dose of 30 mg/kg orally as a single daily dose for 90 days (from day -100 to day-10). Hydroxyurea dosing will be based on adjusted body weight in participants weighing \>125% ideal body weight.

Thiotepa is part of the bone marrow transplant preparative regimen. Thiotepa will be administered at a dose of 10mg/kg intravenously (IV) over 2 hours or per institutional guidelines on day -7. Thiotepa dosing will be based on adjusted body weight in patients weighing \>125% ideal body weight.

Fludarabine is part of the bone marrow transplant preparative regimen. Fludarabine 30 mg/m2/day will be administered from day -7 to day -3 (for a total of 150 mg/m2 over 5 consecutive days) and administered intravenously (IV) over a minimum of 30 minutes. In participants weighing \> 125% ideal body weight, fludarabine will be dose based upon adjusted body weight.

"Cyclophosphamide is part of the bone marrow transplant preparative regimen. Cyclophosphamide will be administered on days -6 and -5 prior to bone marrow infusion at a dose of 14.5 mg/kg intravenously (IV) infused over 1-2 hours.~Post bone marrow infusion cyclophosphamide will be infused on days +3 (between 60 and 72 hours post marrow infusion) and +4 (approximately 24 hours after day +3 dose) at a dose of 50 mg/kg IV infused over 1-2 hours.~For participants weighing more than 125% of their ideal body weight, dosing will be based on adjusted ideal body weight."

Rabbit anti-thymocyte globulin (ATG) is part of the bone marrow transplant preparative regimen. It is an infusion of rabbit-derived antibodies against human T cells used for prevention of acute rejection in organ transplantation. Rabbit ATG will be administered on day -9 at 0.5 mg/kg and on days -8 and -7 at 2 mg/kg (for a total dose 4.5 mg/kg).

Participants will receive 200 cGy of TBI in a single fraction.