The Transplant Preparative Regimen The treatment regimen administered to patients immediately preceding transplantation is designed to eradicate the patient's underlying disease and, in the setting of allogeneic transplantation, immunosuppress the patient adequately to prevent rejection of the transplanted marrow. The appropriate regimen therefore depends on the disease setting and source of marrow. For example, when transplantation is performed to treat severe combined immunodeficiency and the donor is a histocompatible sibling, no treatment is required because no host cells require eradication and the patient is already too immunoincompetent to reject the transplanted marrow. For aplastic anemia, there is no large. | Chapter 108. Hematopoietic Cell Transplantation Part 3 The Transplant Preparative Regimen The treatment regimen administered to patients immediately preceding transplantation is designed to eradicate the patient s underlying disease and in the setting of allogeneic transplantation immunosuppress the patient adequately to prevent rejection of the transplanted marrow. The appropriate regimen therefore depends on the disease setting and source of marrow. For example when transplantation is performed to treat severe combined immunodeficiency and the donor is a histocompatible sibling no treatment is required because no host cells require eradication and the patient is already too immunoincompetent to reject the transplanted marrow. For aplastic anemia there is no large population of cells to eradicate and high-dose cyclophosphamide plus antithymocyte globulin are sufficient to immunosuppress the patient adequately to accept the marrow graft. In the setting of thalassemia and sickle cell anemia high-dose busulfan is frequently added to cyclophosphamide in order to eradicate hyperplastic host hematopoiesis. A variety of different regimens have been developed to treat malignant diseases. Most of these regimens include agents that have high activity against the tumor in question at conventional doses and have myelosuppression as their predominant dose-limiting toxicity. Therefore these regimens commonly include busulfan cyclophosphamide melphalan thiotepa carmustine etoposide and total-body irradiation in various combinations. Although high-dose treatment regimens have typically been used in transplantation the understanding that much of the antitumor effect of transplantation derives from an immunologically mediated GVT response has led investigators to ask if less-intensive nonmyeloablative regimens might be effective and more tolerable. Evidence for a GVT effect comes from studies showing that posttransplant relapse rates are lowest in patients who develop acute and .
