One of the major challenges in the field of allo-SCT is to find a balance between the harmful induction of graft-versus-host disease (GVHD) and the beneficial graft-versus-leukemia (GVL) response, both mediated by donor T cells recognizing antigens expressed on cells of the recipient. Complete removal of T cells from the graft results in abrogation of severe GVHD, but is also frequently associated with removal of the immunity against infectious agents and the anti-tumor efficacy (GVT effect), which is reflected by an increased incidence of infectious complications and (early) disease relapses after T cell depleted allo-SCT. The investigators hypothesize that the prophylactic adoptive transfer of donor-derived central memory T cells is a safe and tolerable method to improve overall survival after HSCT.