Unfortunately, mortality after MAB conditioning is still considerable, mainly due to therapy related mortality, graft-versus-host disease, infections, or relapse. Currently, the NMA conditioning is used more frequently, which is far less toxic. Nonmyeloablative regimens have relied on the immunological anti-leukemia effect (graft-versus-leukemia), to prevent relapsing disease. This anti-leukemia effect, however, needs time to develop, which makes it necessary to be in control over the disease pre-transplantation as much as possible. This extends the time the immune system of the donor has to develop an adequate anti-leukemia effect, which is especially important in the (very) poor risk group patients since they have the highest chance of relapse.