Some people have health conditions that would make it more risky to wipe out all of their bone marrow before a transplant. For those people, doctors can use a type of allogeneic transplant that’s sometimes called a mini-transplant . Compared with a standard allogeneic transplant, this one uses less chemo and/or radiation to get the patient ready for the transplant. Your doctor may refer to it as a non-myeloablative transplant or mention reduced-intensity conditioning (RIC) . The idea here is to kill some of the cancer cells, some of the bone marrow, and suppress the immune system just enough to allow donor stem cells to settle in the bone marrow.
Unlike the standard allogeneic transplant, cells from both the donor and the patient exist together in the patient’s body for some time after a mini-transplant. But slowly, over the course of months, the donor cells take over the bone marrow and replace the patient’s own bone marrow cells. These new cells can then develop an immune response to the cancer and help kill off the patient’s cancer cells — the graft-versus-cancer effect.
One advantage of a mini-transplant is the lower doses of chemo and/or radiation. And because the stem cells aren’t all killed, blood cell counts don’t drop as low while waiting for the new stem cells to start making normal blood cells. This makes it especially useful in older patients and those with other health problems who aren’t strong enough for a standard allogeneic stem cell transplant. It may rarely be used in patients who have already had a transplant.
Mini-transplants treat some diseases better than others. They may not work well for patients with a lot of cancer in their body or those with fast-growing cancers. Also, the lowered immune response can still lead to graft-versus-host disease.
This procedure has only been used since the late 1990s and long-term patient outcomes are not yet clear. There are lower risks of complications, but the cancer may be more likely to relapse (come back). Ways to improve outcomes are still being studied.
Another future possibility is autologous transplant followed by an allogeneic mini-transplant. This is being tested in certain types of cancer, such as multiple myeloma. The autologous transplant can help decrease the amount of cancer present so that the lower doses of chemo given before the mini- transplant can work better. And the recipient still gets the benefit of the graft-versus-cancer effect of the allogeneic transplant.
Syngeneic stem cell transplant
This is a special kind of allogeneic transplant that can only be done when the recipient has an identical twin or identical triplet donor — someone who will always have the same tissue type. An advantage of syngeneic stem cell transplant is that graft-versus-host disease will not be a problem. There are no cancer cells in the transplant, either, as there would be in an autologous transplant. A disadvantage is that this type of transplant won’t help destroy any remaining cancer cells because the new immune system is so much like the recipient’s immune system. Every effort must be made to destroy all the cancer cells before the transplant is done to help keep the cancer from relapsing