Monalizumab (IPH2201), a monoclonal antibody has a non-depleting and purely blocking activity directed with high affinity and specificity against the CD94/NKG2A receptor expressed by subsets of NK cells, activated αβ CD8+ T cells, γδ-T cells and NK T cells. By suppressing the inhibitory signal transduced by NKG2A, IPH2201 enhances the anti-tumor functions, including cytolytic activity of these immune effector cells.The aim of the study is to determine the safety of IPH2201 after allogenic stem cell transplantation.