Inclusion Criteria:

- Acute myeloid leukemia (AML):

- All AML patients beyond 1st remission;

- Intermediate or high risk AML patients (based on South West Oncology Group
[SWOG] cytogenetic criteria) in 1st complete remission

- Myelodysplastic syndrome (MDS)

- Other myeloid malignancies as chronic myelogenous leukemia (CML), CML accelerated
phase, CML blast crisis, chronic myelomonocytic leukemia (CMML) (to be approved by
patient care conference [PCC])

- With Karnofsky Index or Lansky Play-Performance Scale > 70% on pre-transplant
evaluation

- Able to give informed consent (if > 18 years), or with a legal guardian capable of
giving informed consent (if < 18 years)

- Previous autologous or allogeneic HCT is allowed

- Donors must be:

- Human leukocyte antigen (HLA)-identical related donors or

- Unrelated donors matched for HLA-A, B, C, DRB1, and DQB1 defined by high
resolution deoxyribonucleic acid (DNA) typing or mismatched for one HLA allele,
except for HLA-C where no mismatch is allowed

- Able to undergo peripheral blood stem cell collection or bone marrow harvest

- In good general health, with a Karnofsky or Lansky Play Performance score > 90%

- Able to give informed consent (if > 18 years), or with a legal guardian capable
of giving informed consent (if < 18 years)

- Acute lymphoblastic leukemia (ALL): all ALL patients not eligible for other protocols

Exclusion Criteria:

- Receiving umbilical cord blood

- With impaired cardiac function as evidenced by ejection fraction < 35% or cardiac
insufficiency requiring treatment or symptomatic coronary artery disease

- With impaired pulmonary function as evidenced by partial pressure of oxygen (pO2) <
70 mm Hg and diffusing capacity of the lung for carbon monoxide (DLCO) < 70% of
predicted or pO2 < 80 mm Hg and DLCO < 60% of predicted; or receiving supplementary
continuous oxygen

- With impaired renal function as evidenced by creatinine-clearance < 50% for age,
weight, height or serum creatinine > 2x upper normal limit or dialysis-dependent

- With hepatic dysfunction as evidenced by total bilirubin or aspartate
aminotransferase (AST) or alanine aminotransferase (ALT) > 2.0 x upper normal limit
or evidence of synthetic dysfunction or severe cirrhosis

- With active infectious disease requiring deferral of conditioning, as recommended by
an Infectious Disease specialist

- With human immunodeficiency virus (HIV)-positivity or active infectious hepatitis
because of possible risk of lethal infection when treated with immunosuppressive
therapy

- With central nervous system (CNS) leukemic involvement not clearing with intrathecal
chemotherapy and/or cranial radiation prior to initiating conditioning (day -6)

- With life expectancy severely limited by diseases other than malignancy

- Women who are pregnant or lactating because of possible risk to the fetus or infant

- With known hypersensitivity to treosulfan and/or fludarabine

- Receiving another experimental drug within 4 weeks before initiation of conditioning
(day -6)

- Unable to give informed consent (if > 18 years) or with a legal guardian (if < 18
years) unable to give informed consent

- Ineligible donors will be those:

- Deemed unable to undergo marrow harvesting or PBSC mobilization and
leukapheresis

- Who are HIV-positive

- With active infectious hepatitis

- Females with a positive pregnancy test

- Unable to give informed consent (if > 18 years) or with a legal guardian (if <
18 years) unable to give informed consent