Haematopoietic stem cell transplantation (cancer treatment)
Blood can do a lot – even heal. Haematopoietic stem cell transplantation is the transplantation of cells into cancer patients that can replace damaged blood cells in their bone marrow and repair their immune system. There are two types: autologous (with the patient’s own blood) and allogeneic (with blood from a matching donor).
Haematopoietic stem cell transplantation restores the cells in the blood after cancer. This is done by donating haematopoietic stem cells, either from the patient or a matching donor. In the process, intact haematopoietic stem cells are removed and transplanted to a recipient. For example, diseased cells - or cells destroyed as a result of chemotherapy - can be replaced, because the stem cells multiply through division and reproduce themselves.
What preparations are made before the treatment?
Before receiving cells from a matching donor, patients need to complete all treatments that could influence the production of healthy haematopoietic stem cells.
The compatibility of donor and recipient is also checked in advance: for the cells to be accepted, the tissue characteristics – called human leukocyte antigen (HLA) characteristics – of both parties must be as identical as possible.
How is the treatment performed?
Haematopoietic stem cells can be removed by two different methods: Peripheral stem cell collection involves taking blood from a vein. Although some haematopoietic stem cells are always present in the blood, the donor receives a stimulating drug in advance to achieve the number required for a donation.
However, the veins are sometimes too thin to achieve the necessary flow rate required to collect enough stem cells from the vein.
Therefore, in 20% of cases, stem cells are removed via a catheter from a vein in the neck. Stem cells very rarely have to be obtained by bone marrow collection. Bone marrow blood is taken from several parts of the pelvis under general anaesthesia. After the procedure, the donor remains in the hospital for a few days for observation. Their bone marrow reforms within about two weeks.
All collection methods can be used for both autologous and allogeneic transplants.
In autologous transplants, the donor is also the recipient. Since chemotherapy destroys not only cancer cells but also vital haematopoietic stem cells, stem cells are removed from the patient’s blood or bone marrow prior to treatment. These stem cells can then be separated and siphoned off by centrifuging the blood. The cells are then frozen so that they can be returned to the patient after completing chemotherapy, and the haematopoietic stem cell population can return to normal. Since all HLA characteristics are identical when this method is used, the risk of rejection is very low.
Two people are involved in allogeneic transplantation; the tissue characteristics of the donor are matched as closely as possible to those of the recipient. Only identical twins have a complete match. In about a quarter of cases, siblings are suitable donors. Increasingly large databases make it easier to find a matching donor.
What is the success rate of the treatment?
The degree of success of the transplant always depends on the individual’s condition, the type of cancer and the progress of the disease. In the case of lymphomas (cancer in the lymphatic system), for example, the cure rate with haematopoietic stem cell transplantation is between 40% and 50%, which is very high. A complete cure for myeloma (bone marrow cancer) is less likely. However, a haematopoietic stem cell transplant can, delay the disease for longer and improve the patient's quality of life.
What are the complications or risks of the treatment?
Before the transplant, the patient is told about possible risks and complications and prepared for the procedure. The body and immune system are weakened by the chemotherapy before the transplant. This makes the recipient more susceptible to infection.
After an autologous transplant, there is also a risk that the patient's own blood could reintroduce diseased cells into the body, which could lead to a relapse. During an allogeneic transplant, the body may react by rejecting the donated blood or immune system. This means: the more matching HLA values, the lower the risk of rejection. Graft-versus-host-disease is also an immune system reaction: The new immune cells attack the body, which can become life-threatening if not treated.
With every haematopoietic stem cell transplant, there is always a residual risk that the donated cells will not “grow”, i.e., that no new haematopoietic stem cells will form.
What happens after the treatment?
It takes about one to two weeks for the body to start forming new haematopoietic stem cells after the transplant. During this time, the patient stays in the hospital so that any risks and complications can be identified and treated early. During the first year after discharge, regular outpatient check-ups are necessary. Drugs protect the immune system and prevent the transplant from being rejected.