 Allogeneic cord blood stem cell transplantation is a potentially curative therapy for patients with haematological malignancies. We have extensive experience with the use of Cord Blood Transplantation CBT in patients with advanced myeloid malignancies. In adults however, the 40 Non-Relapse Mortality NRM rate observed after CBT conditioned with a myeloablative conditioning has encouraged the development of CBT with Reduced Intensity Conditioning RIC. Our previous national CBT protocol the Minicord French protocol - NCT00797758 showed that RIC CBT can reduce NRM, but relapse remains the main post-transplant event 30 at one year. Thus, the development of reduced toxicity rather than RIC conditioning for CBT is warranted in order to improve the outcome of such transplants by limiting NRM and reducing relapse rate. The Fludarabine, ATG and intensified doses of IV Busulfan 9.6 mgKg total dose regimen is a well-established preparative regimen for reduced-intensitytoxicity conditioning prior to allogeneic stem cell transplantation using peripheral blood stem cells mobilized with G-CSF ClinicalTrials.gov Identifier: NCT00841724. However, such regimen is likely not sufficient to allow for CB cell engraftment. Thiotepa is an alkylating and radio-mimetic agent with a large anti-tumor activity including leukemic cells, the ability to cross the blood-brain barrier and to improve engraftment of hematopoietic stem cells. This drug has been combined to usual conditioning regimen without increasing the toxicity but improving the engraftment rate and potentially reducing the relapse rate. Thus, in the context of adult CBT for high risk myeloid malignancies, we propose to prospectively evaluate a reduced toxicity conditioning based on the association of Thiotepa, Fludarabine, IV Busulfan and ATG with the objective to achieve acceptable NRM rates, and to allow for improved anti-leukemic control based on the cytotoxic component of the conditioning regimen itself, while waiting for the long term immune-mediated disease control GVL effect. 