Inclusion Criteria:

- Diagnosis of acute lymphoblastic leukemia (ALL), acute myeloid leukemia (AML) or
myelodysplastic syndrome (MDS) and current in complete remission meeting one of the
following:

- <45 years of age who are at least 6 months after initial hematopoietic stem cell
transplant (HSCT)

- <45 years of age and have received sufficient radiation treatment to be
ineligible for total body irradiation (TBI) containing preparative therapy

- Karnofsky performance status >70% or if <16 years of age, a Lansky play score >50

- Adequate major organ function including:

- cardiac: left ventricular ejection fraction >45% by echocardiogram (ECHO/MUGA)

- renal: creatinine clearance >40 mL/min/1.73m^2

- hepatic: no clinical evidence of hepatic failure (e.g., coagulopathy, ascites)

- An acceptable source of stem cells according to current University of Minnesota Bone
Marrow Transplant program guidelines. Acceptable stem cell sources include:

- HLA-matched related or unrelated donor bone marrow (6/6 or 5/6 antigen match)

- HLA-matched related or unrelated donor peripheral blood stem cells

- related or single or double unrelated donor umbilical cord blood (6/6, 5/6 or
4/6 match)

- Women of childbearing age must have a negative pregnancy test and all sexually active
participants must agree to use effective contraception during study treatment

- Written consent (adult or parent/guardian)

Exclusion Criteria:

- eligible for TBI containing preparative regimen

- active uncontrolled infection within one week of study enrollment

- pregnant or lactating female