Conditioning Phase (Preparative Regimen)
Before stem cells can be infused a preparative (or conditioning) regimen must be given.
Conditioning consists of high dose chemotherapy but can also include radiation therapy or the use of monoclonal antibodies as immune modifiers.
The purpose of a conditioning regimen is threefold:
- Myelosuppression / Myeloablation
- Creates space in the bone marrow to allow engraftment of stem cells.
- Immunosuppression / Immunoablation
- Prevents residual mature immune cells of the recipient (in the spleen, lymph nodes, thymus) from rejecting the foreign graft.
- Kill residual tumor or leukemia
- use of “megadose” chemotherapy may kill residual solid tumor cells or leukemia cells not sensitive to standard doses of chemotherapy.
Conditioning regimens are typically classified as either:
- Myeloablative (without stem cell engraftment the patient’s bone marrow will remain aplastic and not recover) or
- Reduced-intensity / non-myeloablative (without stem cell engraftment the patient’s autologous stem cells will eventually recover). Reduced-intensity preparative regimens tend to be more immunosuppressive.
Anti–T-cell agents - for example antithymocyte globulin (ATG) can be added to the conditioning regimen to prevent graft rejection.
Conditioning is generally tolerated reasonably well, though antiemetic therapy is used to prevent the significant nausea that can occur.
Examples of common conditioning regimens (not all inclusive and continually changing):
Disease |
Regimen |
Conditioning Type |
Acute Lymphoblastic Leukemia |
1. Total Body Irradiation (1200 cGy in 6 fractions, given twice daily over 3 days is commonly used) 3. Etoposide
|
Myeloablative |
Acute Myelogenous Leukemia |
1. Busulfan 2. Cyclophosphamide |
Myeloablative |
|
Myeloablative |
|
1. Carboplatin 2. Etoposide 3. Cyclophosphamide/Melphalan
|
Myeloablative |
|
Severe Aplastic Anemia |
1. Cyclophosphamide 2. Antithymocyte Globulin 3. Total Body Irradiation (200 cGy)
|
Reduced-Intensity |
Hemophagocytic Lymphohistiocytosis |
1.Campath-IH (immunosuppressive monoclonal antibody) 2. Melphalan 3. Fludarabine
|
Reduced-Intensity |
Conditioning regimen typically lasts 7-10 days. Patient generally stays in hospital. Following conditioning patient will have the transplant.
Many of the early and late complications of HSCT are the direct result of the conditioning regimen (and the previous therapy received).
