Multicenter Study of Peritransplantation Immunosuppression for Mismatched Hematopoietic Cell Transplantation After Reduced Intensity Conditioning

Inclusion Criteria: * Patients scheduled for mismatched allogeneic HCT * Unrelated donor with maximal 2 antigen or allelic mismatches in HLA-I or HLA-II * Age \>=75, \>=18 years * Patients Age \<=50 if a HCT-CI score \> 2 \[acc. to Sorror et al., 2005\] * Karnofsky Index \>60% * Patients with: * Acute myeloid leukemia in CR (\<5% blasts) * Acute lymphoblastic leukemia in CR (\< 5% blasts) * Myelodysplastic syndrome with up to 20% blasts * Osteomyelofibrosis * Chronic lymphocytic leukemia * High grade Non-Hodgkin Lymphoma in CR or PR * Low grad Non-Hodgkin Lymphoma in CR or PR * M. Hodgkin in CR or PR * Chronic myeloid leukaemia in chronic phase or CR of blast crisis Exclusion Criteria: * Patients with \>5% blasts in BM at the time of transplantation * Progressive or chemorefractory disease * Less than 3 months after preceding HCT * CNS involvement with disease * 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 * Proteinuria \>800 mg/24 h * Respiratory failure necessitating supplemental oxygen or DLCO \<30% * Allergy against murine antibodies * Known allergy/intolerance against sirolimus or one of it's excipients * 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