Tumorablative Allogeneic Hematopoietic Stem Cell Transplantation in the Treatment of High-Risk and Refractory Leukemia — New Concepts and Clinical Practice

The substance of bone marrow transplantation is the organ transplantation. Accurately, it is the grafting of hematopoietic and immunologic system. Comparing to the transplantation of solid organ, in the hematopoietic stem cell transplantation (HSCT), the ill organ, id est. hem‐ atopoietic and immunology system, is ablated by high-dose chemotherapy and total body irradiation(TBI) (conditioning regime). Thus, the normal hematopoietic stem cells could be engrafted and normal function of hematopoietic and immune system could be reconstituted. The standard myeloablative conditioning regimen would be reasonable or enough for the non-malignances of marrow, which needed by replacing therapy, such as marrow failure. However, for treatment of hematopoietic malignances, it maybe not cure the malignance diseases to ablate the normal hematopoietic, immune system and reconstitute the normal function of allogeneic hematopoietic and immune system of patients. Because the leukemic stem cells (LSC) are not only existence in the bone marrow, it might be occurrence in any site of body. For instance, the traditional myeloablative conditioning regimen to treat leuke‐ mia could have striking killing effects of leukemic cells, and residual leukemic cells further eradicated by effect of the graft versus leukemia (GVL), but the malignant cells are not al‐ ways removed at all in the all patients, therefore, relapse post transplantation could be oc‐ curred in the some patients. In fact, the traditional allogeneic myeloablative HSCT could cure or improve outcome of acute leukemic patients with standard risk, however, the dis‐ ease relapse after transplant for acute leukemia with high risk and refractory is 40% to 80% [1-4]. Moreover, the leukemic cells in the majority of relapsed cases originate from inceptive