Inclusion Criteria:

   1. Aged ≤ 21 years.

   2. Acute myeloid leukemia (AML) OR acute leukemia of ambiguous lineage (acute
   undifferentiated leukemia or mixed phenotype acute leukemia), specified as either
   refractory (persistent leukemia after at least 2 courses of induction chemotherapy) or
   relapsed, and further defined as any one of the criteria below:

      1. Bone marrow specimen ≥ 5% leukemic blasts by flow, as assessed by Hematologics
      Inc.

      2. A single bone marrow specimen with at least 2 tests demonstrates ≥ 1% leukemic
      blasts by flow cytometry (as assessed by Hematologics Inc), AND at least one of
      the following:

         - Karyotypic abnormality with at least 1 metaphase similar or identical to
         diagnosis

         - FISH abnormality identical to one present at diagnosis

         - PCR or NGS-based demonstration of leukemogenic lesion identical to diagnosis

      3. Rising MRD > 0.1% by flow cytometry on ≥ 2 serial samples, as assessed by
      Hematologics Inc.

      4. If an adequate bone marrow sample is not obtained, subjects may be enrolled if
      there is unequivocal evidence of leukemia based on ≥ 5% blasts in the peripheral
      blood

   3. > 60 days has passed since hematopoietic stem cell transplant.

   4. Patients who have undergone previous allogeneic stem cell transplantation who are
   otherwise eligible must also be without evidence of any active graft versus host
   disease (GVHD), and off calcineurin inhibitors for at least 28 days (four weeks) prior
   to therapy. A physiologic dose of prednisone up to 3 mg/m2 (and a maximum of 7.5 mg)
   or equivalent other steroid dose is allowable.

   5. A minimum of 14 days has passed since completion of myelosuppressive therapy or
   gemtuzumab ozogamicin and all nonhematologic toxicities have resolved to Grade 0 or 1.

   6. A minimum of 24 hours has elapsed since the patient has completed any low-dose or
   non-myelosuppressive therapy (e.g., hydroxyurea or low-dose cytarabine (up to 100
   mg/m2).

   7. Lansky (subjects ≤ 16 years old) or Karnofsky (subjects > 16 years old) score ≥ 50.

   8. WBC ≤ 50,000/uL. This may be achieved using cytoreductive therapy such as hydroxyurea
   or low-dose cytarabine (up to 100 mg/m2/dose)

   9. Total bilirubin ≤ 2.0 x institutional upper limit of normal (ULN) for age.

10. AST/ALT ≤ 5 x ULN for age

11. Left ventricular ejection fraction ≥ 40% or ECHO shortening fraction ≥ 25%.

12. Estimated serum creatinine ≥ 60 mL/min/1.73m2

Exclusion Criteria:

   1. Patients receiving or planning to receive ANY concurrent cancer therapy, including
   chemotherapy, radiation therapy, immunotherapy or biologic therapy.

   2. Patients with down syndrome.

   3. Patients with Acute Promyelocytic leukemia (APL) or Juvenile Myelomonocytic Leukemia
   (JMML).

   4. Patients with Bone Marrow Failure Syndrome.

   5. Pregnant subjects or those unwilling to use an effective method of birth control.

   6. Female subjects with infants who do NOT agree to abstain from breastfeeding.

   7. Inability or unwillingness of legal guardian/representative to give written informed
   consent.

   8. Patients with uncontrolled systemic fungal, bacterial, viral or other infection.