Inclusion Criteria:

- Diagnosis of hematologic cancer or other disease, including any of the following:

- Chronic myelogenous leukemia in first or second chronic phase

- Acute lymphoblastic leukemia (ALL), meeting any of the following criteria:

- Relapsed ALL enrolled on a Children's Oncology Group (COG) relapse clinical
trial OR received ≥ 1 round of reinduction therapy (4-6 weeks) and 1 round
of intensive consolidation chemotherapy (3-6 weeks)

- ALL in second complete remission (CR)* after a bone marrow, extramedullary,
or combined bone marrow and extramedullary relapse

- Very high-risk ALL in first CR, defined as any of the following:

- Philadelphia chromosome-positive ALL

- Hypodiploidy (< 44 chromosomes)

- Mixed lineage leukemia rearrangement

- Induction failure

- Acute myeloid leukemia in first or second CR

- Induction therapy must be completed

- Juvenile myelomonocytic leukemia

- Myelodysplastic syndromes

- No clinically evident CNS or extramedullary disease

- No blasts seen on cerebrospinal fluid cytospin

- Post-relapse reinduction therapy must be completed

- Not planning to receive reduced-intensity conditioning regimen

- Not planning to receive a graft that has undergone T-cell depletion

- No Down syndrome

- Matched sibling donor must be available and must be enrolled on ASCT0631D companion
study

- Karnofsky performance status (PS) 60-100% (patients > 16 years of age) OR Lansky PS
60-100% (patients ≤ 16 years of age)

- AST or ALT < 5 times upper limit of normal for age

- Bilirubin < 2.5 mg/dL (unless due to Gilbert's syndrome)

- Creatinine clearance or radioisotope glomerular filtration rate ≥ 70 mL/min OR serum
creatinine base on age and/or gender as follows:

- 0.4 mg/dL (1 month to < 6 months of age)

- 0.5 mg/dL (6 months to < 1 year of age)

- 0.6 mg/dL (1 to 2 years of age)

- 0.8 mg/dL (2 to < 6 years of age)

- 1.0 mg/dL (6 to < 10 years of age)

- 1.2 mg/dL (10 to < 13 years of age)

- 1.5 mg/dL (male) or 1.4 mg/dL (female) (13 to < 16 years of age)

- 1.7 mg/dL (male) or 1.4 mg/dL (female) (≥ 16 years of age)

- Shortening fraction ≥ 27% by echocardiogram OR LVEF ≥ 50% by radionuclide angiogram

- FEV_1, FVC, and DLCO ≥ 60% OR meets the following criteria (for patients unable to
cooperate for pulmonary function tests):

- No evidence of dyspnea at rest

- No exercise intolerance

- No requirement for supplemental oxygen therapy

- Not pregnant or nursing

- No known HIV

- No known uncontrolled fungal, bacterial, or viral infections

- Patients acquiring fungal disease during induction therapy may proceed if they
have a significant response to antifungal therapy with no or minimal evidence of
disease remaining by CT scan

- No prior allogeneic or autologous stem cell transplantation