Transplantation of donor stem cells is carried out in a similar way to autologous transplantation. Allogeneic stem cell transplantation has two advantages, but also one major disadvantage.
One advantage is that certain immune cells are transplanted along with the donated stem cells, and these can help to fight any remaining cancer cells in the recipient’s body. This beneficial effect is called "graft-versus-disease effect." Another advantage is that no cancer cells will be transmitted because the stem cells were taken from a healthy person.
The disadvantage of this kind of transplantation is that the donor's immune cells might start to attack tissue cells in the recipient's body. This kind of reaction is called a "graft-versus-host effect."
It mostly affects the skin, the intestines and the liver. Acute graft-versus-host disease has four degrees of severity. A mild reaction (stage 1) can cause rashes, but will not affect the success of the transplantation. But more severe reactions (stages 2 to 4) can lead to more serious, sometimes life-threatening problems that need intensive treatment.
Sometimes rejection reactions last a long time, or only start after a few months. This is called chronic graft-versus-host disease. It is an immune response that is similar to an inflammation, affecting tissue in the recipient’s body.
Although it does not affect the production of new blood cells, it can cause several serious and debilitating problems, such as breathing difficulties, joint ache, diarrhea and problems with the mucous membranes, skin or eyes. It can also affect other organs such as the liver. People with a chronic rejection reaction might have to take long-term medication.
To try to prevent a severe transplant rejection, it is important to find a stem cell donor whose tissue type matches the recipient’s tissue type as closely as possible. The ideal donor would be an identical twin whose tissue type is exactly the same as the recipient’s. But this is only very rarely the case.
Stem cells from close relatives are a good alternative. If there is no suitable related donor, unrelated persons can also donate blood stem cells. Here, too, the donor’s tissue type should be as similar as possible to the recipient’s tissue type.
A number of national and international databases have been set up to find suitable stem cell donors. People who would like to donate stem cells can register with a database. There are currently 29 databases responsible for registering donors in Germany. Their contact details can be found on the German National Bone Marrow Donor Registry (ZKRD) website. This central registry collects all data from the different donor databases and also coordinates cooperation with various international databases.