The goal of this prospective study is to assess the overall mortality (whether related to relapse/progression or toxicity - TRM-) at one year after allogeneic stem cell transplantation prepared by a so-called reduced-toxicity "submyeloablative" conditioning regimen in patients with hematological malignancies.

Inclusion Criteria:

• Patients affiliated to a social security reimbursement system
• Adults (men or women) aged between 18 and 65 years
• Negative test for pregnancy
• ECOG 0-1 or Karnofsky Index ≥ 70%
• Availability of an HLA-identical sibling donor, or an HLA-matched unrelated donor (10/10 HLA compatibility in A, B, C, DRB1, DQB1 (a single allelic mismatch at the level of Cw can be accepted)
• Life expectancy > 6 months
• Signed informed consent
• Diagnosis of an hematological malignancy that is considered to be eligible for an allogeneic stem cell transplantation

Exclusion Criteria:

• Pregnant woman or not willing to take effective contraception
• Classical contra-indications to the allogeneic stem cell transplantation procedure
• Any contra-indication to the use of the drugs contained within the conditioning regimen according to the summary of product characteristics
• Patients aged < 50 years and deemed to be eligible for a "standard" or conventional myeloablative conditioning regimen
• An HLA-matched sibling donor who has a contra-indication for stem cell mobilization and collection
• History of uncontrolled psychiatric condition
• Patients who have participated to another trial testing an experimental drug within one month prior to inclusion in this protocol.