Umbilical Cord Blood Transplant for Children With Myeloid Hematological Malignancies

In this study, the investigators will use busulfan and cyclophosphamide (BuCy) backbone with the addition of fludarabine as the preparative Stem Cell Transplant (SCT) regimen. As an attempt to improve engraftment rate and reduce infections, the investigators are going to incorporate fludarabine in the conditioning regimen. The use of a BuCy backbone has been widely used and comparable to total body irradiation and cyclophosphamide (Cy/TBI) regimen. Encouraging data on adding fludarabine to the SCT regimen have been reported. A fludarabine-based, conditioning regimen, with adequate immunosuppressive activity could conceivably allow engraftment of stem cells from alternative donors in hematologic malignancies patients with acceptable engraftment rates and low transplant-related mortality. Regimen-related toxicity is believed to be a major contributing factor to GVHD. Therefore this approach may also lead to reduced GVHD, as some investigators have suggested. In an attempt to decrease the rate of viral infection and reactivation, the investigators will avoid ATG (Thymoglobulin) / Campath (anti-CD52), and instead administer Mycophenolate Mofetil (MMF). The addition of fludarabine should compensate any increase risk of graft failure with the removal of the ATG/Campath. The investigators anticipate that the removal of ATG/Campath will facilitate immune reconstitution more efficiently after receiving a UCBT.