Single vs Double Umbilical Cord Blood Transplants in Children With High Risk Leukemia and Myelodysplasia (BMT CTN 0501)

BACKGROUND: In nearly every large single center or registry analysis of outcomes after UCB transplantation, cell dose is identified as an important factor influencing the incidence and rate of hematopoietic recovery, risk of transplant-related mortality, and probability of survival. Pilot data suggest that infusion of two partially human leukocyte antigen (HLA)-matched UCB units, which always augments the graft cell dose, is safe and may improve neutrophil recovery and survival. To determine whether the infusion of two UCB units enhances survival, a multi-center, open-label, randomized trial is proposed. As adequate single UCB units can be identified for more than 80% of pediatric recipients (in contrast to less than 30% for adults), this study will be open only to pediatric patients. The population will be restricted to patients with high-risk hematologic malignancy, the most common indication of UCB transplantation in children. DESIGN NARRATIVE: Participants will include patients 1 to 21 years of age with a diagnosis of hematological malignancy and with two partially HLA-matched UCB units. Units must be HLA-matched at 3 of 6 HLA-A and B (intermediate resolution molecular typing) and DRB1 (high resolution molecular typing) with each other and 4 of 6 with the recipient. Two appropriately HLA-matched units must be available such that one unit delivers a pre-cryopreserved, nucleated cell dose of at least 2.5 x 10\^7 per kilogram and the second unit delivers at least 1.5 x 10\^7 per kilogram. Patients will be randomized no more than 14 days prior to initiation of conditioning. UCB units will be shipped prior to initiation of conditioning. The preparative regimen will consist of the following: * Fludarabine: 25 mg/m2/day IV on Days -10, -9, and -8. * Total Body Irradiation (TBI): 165 cGy twice daily on Days -7, -6, -5, and -4. * Cyclophosphamide: 60 mg/kg/day x 2 on Days -3 and -2. * Day 0 will be the day of the UCB transplant. The Graft-vs-Host-Disease (GVHD) prophylaxis regimen will be mycophenolate mofetil (MMF) 15 mg/kg IV BID on Day -3 to Day + 45 and cyclosporine A (CSA) to maintain level 200-400 ng/mL beginning on Day -3. Patients will be followed for at least 24 months post-transplant.