Immunoevasive Tactics Employed by Myeloid Malignancy After Allogeneic Stem Cell Transplantation

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.