Allogeneic Stem Cell Transplantation Followed By Targeted Immune Therapy In Average Risk Leukemia

Inclusion Criteria: Disease Status * AML 1st complete remission (CR) with a matched family donor (excluding Downs Syndrome, acute promyelocytic leukaemia (APL), poor cytogenetics (12p, 5q, -7 and FMS-like tyrosine kinase 3 (FLT3) mutations or duplication t(9;11) and others)) and patients consented to and registered on an upfront AML COG study with a matched family donor) * AML 1st CR (excluding Downs Syndrome, APL, and chromosome translocation (8;21) or inversion (16) or poor cytogenetics (12p, 5q, -7, FLT3 mutation or duplication t(9;11) and others)) with unrelated donor * AML 2nd CR * Myelodysplastic Syndrome (MDS) and ≤ 5% bone marrow myeloblasts at diagnosis (de novo patients only) * Juvenile Myelomonocytic Leukemia (JMML) and ≤ 5% bone marrow myeloblasts at diagnosis In regards to disease immunophenotype, disease must express a minimum of ≥10% Cell Differential 33 (CD33) positivity for patients with AML Organ Function: Patients must have adequate organ function as defined below: Adequate renal function defined as: * Serum creatinine \< 1.5 x normal, or * Creatinine clearance or radioisotope glomerular filtration rate (GFR) 40 ml/min/m2 or \> 60 ml/min/1.73 m2 or an equivalent GFR as determined by the institutional normal range Adequate liver function defined as total bilirubin 2.0 x upper limit of normal (ULN), or serum glutamic-oxaloacetic transaminase (SGOT)(aspartate aminotransferase (AST)) or serum glutamic-pyruvic transaminase (SGPT)(alanine aminotransferase (ALT)) \< 5.0 x ULN Adequate cardiac function defined as: * Shortening fraction of ≥ 25% by echocardiogram, or * Ejection fraction of ≥ 45% by radionuclide angiogram or echocardiogram Adequate pulmonary function defined as: * Diffusion capacity of the lung for carbon monoxide (DLCO) ≥ 40% by pulmonary function tests (PFT) (Uncorrected) * For children who are uncooperative, no evidence of dyspnea at rest, no exercise intolerance, and a pulse oximetry \> 94% on room air Exclusion Criteria: * Patients with active central nervous system (CNS) AML/JMML disease at time of preparative regimen * Secondary MDS * Poor cytogenetics (12p, 5q, -7, FLT3 mutation or duplication) * Female patients who are pregnant (positive human chorionic gonadotropin(hCG)) * Karnofsky \<70% or Lansky \<50% if 10 years or less * Age \>30 years * Seropositive for Human Immunodeficiency Virus (HIV) * Patients consented to and registered on an upfront Children's Oncology Group (COG) AML study with a matched family donor