This study is an extension to younger patients of the currently ongoing national, multicenter, open-label, randomized phase III HAPLOMUDELDERLY which evaluates elderly patients with hematological malignancies, justifying an allo-HSCT from an alternative donor when a MRD has not been identified. It will extend the investigation of these two modalities of allo-HSCT to younger patients which are eligible to RIC.

Inclusion Criteria:

• Patients with hematological malignancy
• Age<55 years
• HCT-CI score ≥ 3 or non-eligible for myeloablative regimen
• Patients without a matched related donor
• Patients eligible for an allogeneic HSCT from an alternative donor
• Able to comply with the protocol
• Written informed consent
• Patient affiliated to the national "Social Security" regimen or beneficiary of this regimen

Exclusion Criteria:

• Clinical or biological contraindication to allogeneic HSCT
• Pregnant or breast-feeding women.
• Patient considered socially or psychologically unable to comply with the treatment and the required medical follow-up.
• Severe concomitant disease