Inclusion Criteria:

- Histologically confirmed AML in complete or partial remission or MDS using WHO
classification undergoing alloHSCT

- High resolution typing HLA-matched related or unrelated donor. Donors may be
mismatched at single antigen at HLA-A, -B or -DR locus plus possible single antigen
mismatch at HLA-C according to institution guidelines. Two-antigen mismatch at a
single locus is not allowed.

- Age ≥ 18

- creatinine < 1.5 times the institutional ULN or creatinine clearance (calculated by
the Cockroft and Gault method) ≥ 30 mL/min

- bilirubin < 1.5 times the institutional ULN

- AST, ALT and alkaline phosphatase < 2.5 times the institutional ULN.

Exclusion Criteria:

- History of previous alloHSCT prior to the current alloHSCT.

- Persistent AML or MDS after alloHSCT.

- Positive serology for HIV.

- Pregnancy or nursing.

- Other cancers less than or equal to 2 years prior study entry except: basal cell
carcinoma of the skin, squamous cell carcinoma of the skin, carcinoma in situ of the
cervix, carcinoma in situ of the breast, prostate cancer stage T1a or T1b.

- Uncontrolled active infections requiring intravenous antibiotics. Clinically
significant systemic illness (e.g. serious active infections or significant cardiac,
pulmonary, hepatic or other organ dysfunction), which, in the judgment of the
Principal or Associate Investigator would compromise the patient's ability to
tolerate protocol therapy.

- Known or suspected hypersensitivity to decitabine.

- Patients may not be receiving any other investigational agents.

- General or specific changes in patient's condition that render the patient
unacceptable for further treatment in judgment of the investigators.