Advantages and limitations of (non-)myeloablative allogeneic stem cell transplantation

Allogeneic stem cell transplantation (allo-SCT) is the treatment of choice for a variety of malignant diseases, not only as a method to regain haematopoiesis after myeloablative therapy, but also for its apparent antitumour effect. However, treatment-related morbidity and mortality are considerable. A potential way to overcome this problem is by decreasing the intensity of chemotherapy and/or radiotherapy given prior to transplantation. This reduced-intensity conditioning regimen is the basis of non-myeloablative allo-SCT (also referred to as mini SCT), a new treatment modality that relies more heavily on the antitumour effect exerted by the donor cells than on the antitumour effect of the conditioning therapy. The aim of this article is to place the concept of non-myeloablative SCT in a historical context and to discuss the advantages and disadvantages of regular myeloablative SCT compared with non-myeloablative SCT. Furthermore, human trials regarding non-myeloablative SCT are reviewed, and several experimental techniques are discussed that aim to augment the antitumour effect of an allogeneic graft.