Inclusion Criteria:

          -  Matched sibling donor (HLA 8/8), if available, or a unrelated partially HLA matched
             single unit based on the following priority:

               -  1st priority: 4/6 matched unit, cell dose >5 x 10-7 nucleated cells/kg

               -  2nd priority: 5/6 matched unit, cell dose > 4 x 10-7 nucleated cells/kg

               -  3rd priority: 6/6 matched unit, cell dose > 3 x 10-7 nucleated cells/kg

          -  Patients aged ≤ 3 years at diagnosis (not age of transplant) with hematological
             malignancy as detailed below:

               -  Acute myeloid leukemia: high risk CR1 as evidenced by:

                    -  High risk cytogenetics t(4;11) or other MLL rearrangements; chromosome 5, 7,
                       or 19 abnormalities; complex karyotype (>5 distinct changes); ≥ 2 cycles to
                       obtain complete response (CR); CR2 or higher; Preceding myelodysplastic
                       syndrome (MDS); All patients must be in CR or early relapse (i.e., <15%
                       blasts in BM).

                    -  Acute lymphocytic leukemia: high risk CR1 as evidenced by: High-risk
                       cytogenetic: t(4;11) or other MLL rearrangements; hypodiploid; t(9;22); >1
                       cycle to obtain CR; CR2 or higher; All patients must be in CR as defined by
                       hematological recovery, AND <5% blasts by light microscopy within the bone
                       marrow with a cellularity of ≥15%.

               -  Myelodysplasia (MDS) IPSS Int-2 or High risk (i.e. RAEB, RAEBt) or refractory
                  anemia with severe pancytopenia or high risk cytogenetics. Blasts must be < 10%
                  by a representative bone marrow aspirate morphology.

               -  Persistent or rising minimal residual disease (MRD) after standard chemotherapy
                  regimens: Patients with evidence of minimal residual disease at the completion of
                  therapy or evidence of rising MRD while on therapy. MRD will be defined by either
                  flow cytometry (>0.1% residual cells in the blast gate with immune phenotype of
                  original leukemic clone), by molecular techniques (PCR or FISH) or conventional
                  cytogenetics (g-banding).

               -  New Leukemia Subtypes: A major effort in the field of pediatric hematology is to
                  identify patients who are of high risk for treatment failure so that patients can
                  be appropriately stratified to either more (or less) intensive therapy. This
                  effort is continually ongoing and retrospective studies identify new disease
                  features or characteristics that are associated with treatment outcomes.
                  Therefore, if new high risk features are identified after the writing of this
                  protocol, patients can be enrolled with the approval of two members of the study
                  committee.

          -  Recipients must have a Lansky score ≥ 50% and have acceptable organ function defined
             as:

               -  Renal: glomerial filtration rate > 60ml/min/1.73m^2

               -  Hepatic: bilirubin, AST/ALT, ALP < 5 x upper limit of normal,

               -  Pulmonary function: oxygen saturation >92%

               -  Cardiac: left ventricular ejection fraction > 45%.

          -  Voluntary written informed consent before performance of any study-related procedure
             not part of normal medical care.

        Exclusion Criteria:

          -  Active infection at time of transplantation (including active infection with
             Aspergillus or other mold within 30 days).

          -  History of HIV infection or known positive serology

          -  Myeloablative transplant within the last 6 months.

          -  Evidence of active extramedullary disease (including central nervous system leukemia).