Inclusion Criteria:

        Patients who have undergone T cell depleted allogeneic hematopoietic stem cell
        transplantation at MSKCC for:

          -  De novo myelodysplastic syndromes (MDS): IPSS-1 with poor risk cytogenetics or higher
             IPSS.

          -  Acute myelogenous leukemia (AML) in first remission that required more than 1 cycle of
             treatment to achieve remission or with the following cytogenetic abnormalities: FLT3
             mutation, deletion/monosomy of chromosome 5 or 7, MLL gene rearrangement, or more than
             or equal to 3 cytogenetics abnormalities. Also patients in second or greater
             remission.

          -  Patients with Secondary MDS/AML.

          -  Patients will be considered eligible for the study if after transplant they achieved
             hematologic (<5% blasts) and cytogenetic remission.

          -  Patients will be eligible to enter the study between 60-120 days post transplant.

          -  Age: pediatrics and adults patients - 1 year old-75 years old.

          -  Karnofsky performance status >=60% for patients >16yo and Lansky performance status
             >=60% for patients ≤16yo

          -  Stable blood counts (ANC>1000/uL, Hb>8gr/dL, Plt>50,000/ uL) not supported by
             transfusions.

          -  Renal: Serum creatinine <1.5 ULN

          -  Hepatic: <3xULN ALT and <1.5 total serum bilirubin, unless there is congenital benign
             hyperbilirubinemia.

          -  Cardiac: Adequate cardiac function measured by LVEF>50%. If asymptomatic,
             pretransplant echocardiogram is adequate. If symptomatic, echocardiogram needs to be
             repeated.

          -  Each patient must be willing to participate as a research subject and must sign an
             informed consent form.

        Exclusion Criteria:

        Patients will be excluded from the trial if at time of enrollment:

          -  Active uncontrolled bacterial, fungal or viral infection.

          -  Evidence of uncontrolled graft-versus-host disease.

          -  Pulmonary: new onset hypoxia

          -  Known or suspected hypersensitivity to 5'-azacitadine or mannitol.

               -  Evidence of residual disease either by increased blasts count (>5%) or
                  persistence of previous known cytogenetics abnormalities.

          -  Peripheral blood neutrophil chimerism: less than 95% donor.