The present invention relates, generally, to methods and compositions for allogeneic transplantation. More particularly, the invention relates to the use of alloreactive natural killer cells in order to enhance the efficacy and/or safety of allogeneic grafts in human subjects. The invention allows to increase the engraftment of an allogeneic grafts, even in myelo-reductive conditioning, to protect against GVHD and/or to eradicate malignant cells. The invention is particularly suited in allogeneic hematopoietic transplantations, particularly bone marrow transplantations.