Inclusion Criteria:

- Diagnosis of ALL or AML.

- Prior therapy Patients must have fully recovered from the acute toxic effects of all
prior chemotherapy, immunotherapy, or radiotherapy prior to entering this study.

- ALL patients must have had two or more prior therapeutic attempts defined as

- Persistent (BM blast>5%) initial disease after two induction attempts, or

- Persistent (BM blast>5%) after re-induction attempt for first relapse or

- Relapse after one re-induction attempt (2nd relapse)

- AML patients must have one or more prior therapeutic attempts defined as

- Refractory (BM blast>20%) initial disease after one induction attempts, or

- Persistent (BM blast>5%) initial disease after two induction attempts, or

- Relapse after one induction attempt (1st relapse)

- Relapse after stem cell transplant: Patients are eligible 12 weeks after
allogeneic stem cell transplant as long as patients are not actively being
treated for GvHD and have recovered from transplant-related toxicities. Patients
are eligible 8 weeks from the day of stem cell infusion for myeloablative
autologous stem cell transplant, if hematological and all other eligibility
criteria are met.

- Age: ≤ 21 years.

- Performance status: ECOG 0-2.

- Patients must be free of significant functional deficits in major organs, but the
following eligibility criteria may be modified in individual cases.

1. Heart: a shortening fraction ≥ 28%

2. Liver: total bilirubin < 2 × upper limit of normal; ALT < 3 × upper limit of
normal.

3. Kidney: creatinine <2 × normal or a creatinine clearance (GFR) > 60
ml/min/1.73m2.

- Patients must lack any active viral infections or active fungal infection.

- Patients (or one of parents if patients age < 19) should sign informed

Exclusion Criteria:

1. Pregnant or nursing women.

2. Malignant (except acute leukemia) or nonmalignant illness that is uncontrolled or
whose control may be jeopardized by complications of study therapy.

3. Psychiatric disorder that would preclude compliance.

4. Patients who, in the opinion of the investigator, may not be able to comply with the
safety monitoring requirements of the study.