Inclusion Criteria:

- Patients with either ALL or AML in CR with an indication for allogeneic HCT according
to the following criteria:

- AML: high risk patients with one or more of the following risk factors:

- FLT-3 mutation

- Complex cytogenetics

- abn(3q), -5/5q-, -7/7q-, abn(12p), abn(17p)

- Late CR > induction I

- Age >60

- Patients in 2.CR

- Secondary AML

- Relapse after a preceding allogeneic HCT from an HLA-identical donor

- ALL: high risk patients with one or more of the following risk factors:

- Pro-B-ALL

- Initial WBC >30.000/µL

- CR after day 46 after Induction II

- Complex cytogenetics, t(9,22), t(4,11)

- Early or mature T-ALL

- Initially refractory patients with late CR

- Rising MRD level

- Patients in 2. CR

- Relapse after a preceding allogeneic HCT from an HLA-identical donor

- No HLA-identical donor (not more than 1 antigen mismatch (9/10-Match) or more
than 2 allelic mismatches by high-resolution typing). Critical cases should be
discussed with the PI.

- Age <=65, >=18 years

- Karnofsky Index >60%

Exclusion Criteria:

- Patients with >5% blasts in BM at the time of transplantation

- Less than 3 months after preceding HCT

- CNS involvement with disease

- History of neurologic impairment such as: seizures, severe peripheral neuropathy,
signs of leukoencephalopathy, CNS infection, multiple intrathecal chemotherapies, CNS
irradiation. In case of heavy pretreatment with irradiation or intrathecal
chemotherapy pretransplant CNS MRI and neurological consultation are mandatory

- Fungal infections with radiological progression after receipt of amphotericin B or
active triazole for greater than 1 month.

- Liver function abnormalities with bilirubin >2 mg/dL and elevation of transaminases
higher 2x upper limit of normal.

- Chronic active viral hepatitis

- Ejection fraction <40 % on echocardiography

- Patients with > grade II hypertension by CTC criteria

- Creatinine clearance <50 ml/min

- Respiratory failure necessitating supplemental oxygen or DLCO <30%

- Allergy against murine antibodies

- HIV-Infection

- Female patients who are pregnant or breast feeding, or adults of reproductive
potential not employing an effective method of birth control during study treatment
and for at least 12 months thereafter. (Women of childbearing potential must have a
negative serum pregnancy test at study entry)

- Concurrent severe and/or uncontrolled medical disease (e.g. uncontrolled diabetes,
congestive heart failure, myocardial infarction within 6 months prior to the study,
unstable and uncontrolled hypertension, chronic renal disease, or active uncontrolled
infection) which could compromise participation in the study

- Patients with a history of psychiatric illness or condition which could interfere
with their ability to understand the requirements of the study (this includes
alcoholism/drug addiction)

- Patients unwilling or unable to comply with the protocol

- Unable to give informed consent

- Enrollment in an other trial interfering with the endpoints of this study