Conditioning regimens are also known as preparative regimens. These combinations of chemotherapy or radiation therapy help prepare the patient’s body to receive the donor’s bone marrow.
The purpose of the conditioning regimen varies according to the type of stem cell transplant:
- For autologous transplants, increasing doses of chemotherapy with or without irradiation are given to destroy more malignant cells.
- For allogeneic transplants, the regimen not only destroys remaining malignant cells, but also helps prevent the patient’s body from rejecting the donor’s stem cells.
Historically, the most common types of conditioning regimens for patients receiving allogeneic stem cell transplants have been cyclophosphamide with total body irradiation (TBI) or busulfan and cyclophosphamide. The conditioning regimens for those receiving autologous stem cell transplants vary among centers and by tumor type.
For patients receiving allogeneic transplants, cyclophosphamide, cytarabine (Ara-C) and etoposide (VP-16) are now used in conditioning regimens. TBI is also commonly used. Sometimes busulfan is used instead of TBI when patients cannot receive more radiation therapy. In some cases, antibodies such as OKT3 or anti-thymocyte globulin (ATG) are given to prevent graft rejection. These antibody preparations are designed to recognize T-cells, which are part of the immune system, and destroy them so that they cannot cause graft rejection.
For patients receiving autologous stem cell transplants, the regimens may consist of cyclophosphamide, etoposide (VP-16), carmustine (BCNU), cytarabine (Ara-C), melphalan, cisplatin, carboplatin and busulfan. In many cases, TBI is not given before transplant; instead, radiation to localized sites of disease is given after the autologous transplant. This approach allows higher doses of radiation to be given to specific sites where most tumor cells were found before the transplant. As part of conditioning regimens, chemo is usually given in doses that are 3 to 8 times higher than standard doses given without stem cell support. The increases in doses are permissible because the initial toxicity (destruction of the patient’s marrow) will be overcome by the transplantation of stem cells.
The side effects resulting from a conditioning regimen vary and depend on the chemo drugs used, and whether radiation therapy is given.