Reduced-intensity allogeneic transplantation (sometimes called “mini-transplant” or “nonmyeloablative transplant”) uses lower, less toxic doses of chemotherapy and radiation than the conditioning regimen that is given before standard allogeneic transplantations. This type of transplant may be an option for certain patients who are older, who have organ complications or who are otherwise not healthy or strong enough to undergo standard allogeneic transplantation. With a reducedintensity conditioning regimen, the patient’s blood counts may not fall as low as they would with high-dose chemotherapy. Additionally, the less toxic regimens put less strain on the patient’s major organs, making this regimen more tolerable and safer. Sufficient numbers of reduced-intensity allogeneic stem cell transplants have been performed to conclude that it may be an appropriate treatment for certain older, sicker patients who cannot tolerate a high-dose conditioning regimen.

The success of reduced-intensity transplantation depends on the graft-versustumor (GVT) effect of the donor stem cells, rather than on high-dose treatments to kill the cancer cells. The goal is to have the donor stem cells take up residence in the recipient’s marrow and produce lymphocytes (white blood cells, part of the immune system) that will attack the patient’s remaining blood-cancer cells. The conditioning regimen for a reduced-intensity allogeneic transplantation does not destroy as many cancer cells as the regimen for a standard allogeneic transplantation. But this conditioning regimen—along with potent drugs to suppress the patient’s immune system—should weaken the patient’s immune system enough so that it cannot attack and reject the donor cells, allowing the donor cells to take over the bone marrow and produce a new immune system to fight the cancer. 

In some instances, blood cells from both the donor and the patient may exist in the patient’s bone marrow for some time after transplantation. When the donor’s immune system does not completely replace that of the patient (a state called “mixed chimerism”), the patient may be given an injection of the donor’s lymphocytes (white blood cells) to improve engraftment and possibly the immune system’s antitumor effects. This procedure is called a “donor lymphocyte infusion” (DLI).

Potential Complications

Reduced-intensity allogeneic transplantations carry many of the same risks as standard allogeneic transplantations. One risk is that the patient’s body may reject the donated stem cells before they are able to engraft in the bone marrow. The patient’s immune cells may see the donor’s cells as foreign and destroy them before engraftment can begin. Another risk is that the immune cells from the donor (the graft) may attack healthy cells in the patient’s body (host). This is called “graft-versus-host disease” (GVHD). 

Related Links

• Download or order The Leukemia & Lymphoma Society's free booklet, Blood and Marrow Stem Cell Transplantation.