Allogeneic hematopoietic stem cell transplantation (allo-HSCT) is still the only treatment available to cure acute myeloid leukemia and high risk myelodysplasia. Allo-HSCT has an anti-tumor effect (called the graft versus leukemia effect= GVL) mediated by donor lymphocytes. This GVL effect is often associated with graft-versus-host disease (GVHD). Several studies have shown that the relapse incidence is lower in patients developing chronic GVHD. These studies confirm the impact of donor immune system on leukemic residual cells. In fact, the relapse incidence increased in patients with no sign of GVHD. The investigators assume that leukemic cells probably use mechanisms to inhibit the allogeneic response. These escape mechanisms to immunosurveillance have been described in other malignancies. Out of context of the allo-HSCT, in acute myeloid leukemias and myelodysplasia, correlations between the severity of the disease and the presence of regulatory T cells (Tregs) or exhausted T cells (PD1 positive) in the bone marrow and in the blood of patients were described at the time of diagnosis or relapse. Myeloid Derived Suppressive Cells (MDSCs) have been described as capable of inducing Tregs and exhausted T cells in the tumor microenvironment.The investigators want to evaluate the role of myeloid suppressive cells in bone marrow after allo HSCT. They hypothesize that their presence in bone marrow and / or blood recipient is correlated to the relapse incidence.

Inclusion Criteria:

• Patients with acute myeloid leukemia in complete cytological remission with intermediate or high risk prognosis according to ELN 2017
• Patients with myelodysplasia according to the WHO 2016 definition, with IPSS ≥1.5 and disease status is : stable or in partial response or complete response according to IWG 2006.
• Patients with indication of first allo-HSCT with a matched related or unrelated donor
• Patients receiving non-myeloablative or reduced toxicity conditioning
• Patients affiliated to a social security scheme
• Patients who have received a complete information on the organization of the research and signed his informed consent

Exclusion Criteria:

• Patients with an alternative donor (HLA 5/10 or unit cord blood)
• Patients with another active cancer or a history of cancer diagnosed in the previous 5 years
• Patients with uncontrolled infection at the time of inclusion, or with positive HIV (1 + 2) or HTLV (1 + 2), Hepatitis C or active hepatitis B
• Patients referred to in Articles L. 1121-5, L. 1121-7 and L1121-8 of the Public Health Code.