Inclusion Criteria:

- Patients must be greater than or equal to 1 and less than or equal to 21 years of age
at the of study entry.

- Patients must have a diagnosis of ALL or AML.

- ALL patients must be in clinical remission defined as BM morphology <5% blasts and
CNS 1 status.

- AML patients must be in M1 (<5% blasts) or M2 (<20% blasts) marrow status with CNS 1
status.

- Patient must have an ANC greater than or equal to 750/ul.

- Patient must have one of the appropriate donor types as described below:

1. HLA identical sibling donor.

2. Complete matched unrelated donor, (matched at A, B, C, DR B1 and DQ, B1 at the
allelic level based on high resolution typing for Class I and II antigens, 10/10
match).

3. 1 allelic mis-matched unrelated donor (antigen mis-matches are not allowed).

- The stem cell source from the donor must be one of the following:

1. Bone Marrow or Peripheral blood stem cells (PBSC) from a matched related donor.

2. PBSC from an unrelated donor. (Bone marrow is not acceptable for unrelated
donors)

- Karnofsky > 50% for patients > 10 years of age and Lansky > 50% for patients less
than or equal to 10 years of age.

- Female patients of childbearing potential must have a negative serum pregnancy test
confirmed within 2 weeks prior to enrollment.

- Female patients with infants must agree not to breastfeed their infants while on this
study.

- Male and female patients of child-bearing potential must agree to use an effective
method of contraception approved by the investigator during the study.

- Patients must have a calculated creatinine clearance ≥ 70mL/min/m2 as calculated by
the Schwartz formula for estimated glomerular filtration rate (GFR) where GFR
(ml/min/1.73 m2) = k * Height (cm)/serum creatinine (mg/dl). K is a proportionality
constant which varies with age and is a function of urinary creatinine excretion per
unit of body size; 0.45 up to 12 months of age; 0.55 children and adolescent girls;
and 0.70 adolescent boys.

- Total serum bilirubin < 2 mg/dL.

- Aspartate transaminase (AST) and alanine transaminase (ALT) less than or equal to 5 ×
ULN.

- Patient must have a shortening fraction (SF) > 25%. If the SF is <25%, patient must
have an ejection fraction (EF) by MUGA of >30%.

- Patient must have pulmonary function as defined below:

1. DLCO >30%

2. FVC/TLC >30%

3. FEV1 > 30% of predicted

4. Patient is not on continuous oxygen If patient is not old enough or unable to
comply with pulmonary function tests, they must have a pulse ox >92% in room air
and not be on continuous oxygen.

- Patient must have signed informed consent

Exclusion Criteria:

- Patients will be excluded if they have evidence of an active, progressive invasive
infection. All patients with existing infections at the time study entry should be
discussed with the study chair.

- Patients may have stable invasive infections and still be eligible.

- Patients with infections that are responsive to medical or surgical treatment as
shown by radiographic and or microbial assessment may still be eligible.

- Patients will be excluded if they have an active, uncontrolled systemic fungal,
bacterial, viral or other infection. All patients with existing infections at the
time of study entry should be discussed with the study chair.

•An active uncontrolled infection is defined as exhibiting ongoing signs and symptoms
related to the infection (fevers, positive blood cultures, chills, tachycardia, etc)
despite appropriate antibiotics or other treatment.

- Patient has a diagnosis of CML or MDS.

- Patient has CNS 2 or CNS 3 status.

- Patient is HIV positive.

- Current or planned treatment with chemotherapy, radiation therapy, or immunotherapy
other than as specified in the protocol.

- Use of investigational agents within 30 days or any anticancer therapy within 2 weeks
before study entry.

- Have any other severe concurrent disease, or have a history of serious organ
dysfunction or disease involving the heart, kidney (including dialysis patients),
liver, or other organ system that may place the patient at undue risk to undergo
treatment.

- Patients with a systemic fungal, bacterial, viral, or other infection not controlled
(defined as exhibiting ongoing signs/symptoms related to the infection and without
improvement, despite appropriate antibiotics or other treatment).

- Any significant concurrent disease, illness, psychiatric disorder or social issue
that would compromise patient safety or compliance, study participation, follow up,
or interpretation of study results.