Doctors associate two main goals with allogeneic stem cell transplants :
- Firstly, healthy hematopoietic cells can be transferred to a person with blood cancer (leukemia). The cells replace the damaged or dead bone marrow after aggressive chemotherapy or radiation.
- On the other hand, the newly formed immune cells attack the patient's remaining tumor cells.
Doctors also refer to allogeneic stem cell transplantation as the graft versus leukemia reaction (graft versus leukemia).
Leukemia means "white blood" and refers to a variety of blood cancers that originate from the white blood cells (leukocytes) @ kalsoom /AdobeStock
For leukemia patients or people with rare brain tumors, doctors kill cancer cells with chemotherapy or radiation therapy.
However, both the leukemia and the intensive treatment destroy the bone marrow. As a result, patients no longer have their own blood formation and immune system.
The patient therefore requires a stem cell transplant following cancer therapy. The new stem cells form a new bone marrow and new blood cells.
Specialists speak of autologous stem cell transplantation when:
- The blood stem cells come from the patient themselves
- Doctors remove them before chemotherapy, purify them and then give them back
In this procedure, the donor and recipient are therefore one and the same person.
Allogeneic stem cell transplantation, on the other hand, is when
- The cancer patient (recipient) receives stem cells from another person (donor)
In most cases, this person is from the patient's own family. However, unrelated people can also be considered as donors.
Human bone marrow is the most important blood-forming organ in humans @ 7activestudio /AdobeStock
Since the donor and recipient are different people, the donor must have similar immune cell surface markers.
These human leukocyte antigens (HLA) are present on all cells in the body. They signal to the immune system that it is "at home" and that everything is in order.
This is ultimately one of the reasons why our immune system does not turn against our own body. Foreign surface markers, on the other hand, are foreign, which is why our immune system usually attacks them.
In allogeneic stem cell transplantation, doctors transfer a "foreign" hematopoietic system into a recipient. The resulting immune system corresponds to that of the donor. It would therefore classify the recipient's cells as foreign and attack them (graft-versus-host reaction).
To prevent this from happening, however, doctors must find a suitable donor before the allogeneic stem cell transplant. This is done on the basis of the HLA pattern.
This means that the bone marrow should form blood and immune cells from the donor cells that are similar to those of the recipient. This significantly reduces the risk of a rejection reaction.
If there is an HLA-compatible donor (e.g. within the family), the donor's blood or bone marrow stem cells can be collected.
Doctors then prepare the recipient (usually a leukemia patient) for the transplant using high-dose chemotherapy or radiotherapy.
The chemotherapy or radiotherapy eradicates the body's own bone marrow with the cancer cells. As a result, the patient has no hematopoiesis and no immune system after the treatment.
The recipient then receives the donor cells by means of a blood transfusion. The allogeneic stem cells migrate into the bone marrow cavities and form a new bone marrow there.
After around three weeks, the new bone marrow has grown from the stem cells and the recipient's blood values normalize.
Once hematopoiesis begins, a new immune system develops. If no more tumor cells can be detected, the patient is cured.
Around six months after the stem cell transplant, the patient has the blood group of the stem cell donor @ Elnur /AdobeStock
An allogeneic stem cell transplant is the only chance of recovery for most patients. However, the therapy method is not completely risk-free.
This is because there is a risk that the "donor bone marrow" will not grow.
The much greater risk with an allogeneic stem cell transplant is that the newly formed immune system attacks the recipient's body, which doctors also call graft-versus-host disease. To prevent this, it is particularly important to achieve the highest possible HLA match in advance.
After stem cell transplantation, medication can suppress the immune response. However, this increases the risk of infection.
The high-dose chemotherapy and whole-body radiotherapy damage the germ cells of men and women. They can therefore become infertile as a result of the therapy.
You should therefore talk to your doctor about the possibility of cryopreserving ("freezing") sperm and/or eggs before the therapy. In this way, it may still be possible to have children at a young age.
Another late consequence can be secondary tumors caused by high-dose chemotherapy or radiation. Nevertheless, allogeneic stem cell transplantation is often the only option for many patients.
Most patients who are eligible for an allogeneic stem cell transplant suffer from malignant blood diseases (leukemias). Leukemias belong in the hands of specialists in the fields of hematology and oncology. These fields are part of internal medicine.
You should make sure to seek advice from specialized tumor centers. These are, for example, centers for haemato-oncology or stem cell transplantation centers. These can now be found at numerous university hospitals throughout Germany. An overview of experienced specialists for allogeneic stem cell transplants and specialized tumor centers can be found above.