Chronic Graft-versus-host Disease (cGvHD) Prophylaxis With or Without ATG Prior to Stem Cell Transplantation (SCT) From HLA-identical Siblings in Patients With Acute Leukemia

Inclusion Criteria: * Acute myeloid leukemia in first or subsequent complete remission (de-novo or secondary AML) * Acute lymphoblastic leukemia in first or subsequent complete remission * Patient's age: 18 - 65 years * Myeloablative standard conditioning * HLA-identical sibling (HLA-A, HLA-B, HLA-DRB1 and HLA-DQB1) * No major organ dysfunctions * Patient's written consent Exclusion Criteria: * No complete remission at time of randomization * Severe irreversible renal, hepatic, pulmonary or cardiac disease, such as * Total bilirubin, SGPT or SGOT 5 times upper the normal level * left ventricular ejection fraction \<30% * Creatinine clearance \<30 ml/min * DLCO \<35% and/or receiving supplementary continuous oxygen * Positive serology for HIV * Pregnant or lactating women * Serious psychiatric or psychological disorders * Progressive invasive fungal infection at time of registration