Inclusion Criteria:  Group A (adults):  Adult patients affected by acute leukemia (AML, ALL) defined as:  Acute Myeloid Leukemia (AML):  High risk AML in CR1; any adverse genetic abnormality, secondary or therapy related AML excluding good risk genetic abnormalities Chemo-refractory relapse (MRD+) ≥ CR2  Acute Lymphoblastic Leukemia (ALL):  Chemo-refractory relapse (MRD+) High risk in CR1; Philadelphia (like) or any poor risk feature ≥ CR2 Patient eligible for an allogeneic HSCT Age ≥ 21y and clinical condition compatible with allogeneic bone marrow transplantation Karnofsky index ≥ 70% Patients with normal organ function  Group B (pediatrics):  Pediatric patients affected by acute leukemia (AML, ALL) defined as:  Acute Myeloid Leukemia (AML):  High risk AML in CR1; any adverse genetic abnormality, secondary or therapy related AML excluding good risk genetic abnormalities, Chemo-refractory relapse (MRD+) ≥ CR2  Acute Lymphoblastic Leukemia (ALL):  Chemo-refractory relapse (MRD+) High risk in CR1; Philadelphia (like) or any poor risk feature ≥ CR2 Patient eligible for an allogeneic HSCT Age < 21y at the time of inclusion Absence of a matched sibling donor (MSD) Lansky ≥ 70% / Karnofsky ≥ 70% Patients with normal organ function  Exclusion Criteria:  Groups A and B:  Planned use of an HLA matched CB (8/8 allele matched). Prior therapy with allogeneic stem cell transplantation Treatment with another cellular therapy within one month before inclusion