First, cells from a fully HLA-matched donor are used whenever possible to reduce the risk of rejection. Low-dose radiation, with or without chemotherapy, is used before the transplant to suppress, rather than destroy the patient's immune system. Immunosuppressant drugs are then used to maintain the immune suppression at the proper level. Carefully controlling the level of immunosuppression allows the donor stem cells to take hold and begin producing a full range of blood and immune system cells in the patient. For more information, go to:
Chimerism is a condition where cells in an organism come from two different individuals. The end result of a blood or marrow transplant is that blood and marrow cells come the donor, while all other types of cells come from the patient. The term "full" chimerism means that all blood and marrow cells in the patient came from the donor. The term "mixed" chimerism means that some cells came from the donor and some came from the patient. After a transplant, the change from patient blood and marrow cells to donor cells does not occur all at once. This change occurs more slowly after a mini or non-myeloablative stem-cell transplant as compared to a myeloablative transplant. With both types of transplant, the immune cells of the donor help this change to occur. For more information, go to:
Unfortunately, mini or non-myeloablative transplants can't be used in every situation. This type of treatment works best for treatment of certain diseases and is not effective for other diseases, depending on whether immune cells of the donor can eliminate malignant cells in the recipient. Immune cells of the donor are most effective when the patient has a low number of malignant cells. In order to have a successful outcome, the patient's disease might have to be in remission before a non-myeloablative transplant. Clinical trials are in progress to find out whether mini or non-myeloablative transplants can be successful for patients who do not have a fully HLA-matched donor. Further research is needed to determine whether mini-transplant is a safe and effective treatment for all types of disease that are treated by stem-cell transplant. For more information, go to:
Because the first mini-transplants were performed less than 10 years ago, it's difficult to say whether the long-term effects will be similar to those that occur after a myeloablative transplant. The number of patients with long-term effects due to radiation will likely be lower after a non-myeloablative transplant. For example, the risk of skin cancer will likely be lower after a non-myeloablative transplant, since higher levels of radiation have been associated with an increased risk of skin cancer. Long-term effects related to immunosuppressive medications would depend on the dose and duration of treatment. Analysis of data on long-term survivors of non-myeloablative transplants will be needed to determine whether there are any differences between the two types of transplant.