Allogeneic bone marrow transplant is a procedure in which healthy stem cells taken from the bone marrow of a suitable donor are placed in place of the patient's own stem cells. In allogeneic stem cell transplantation, the stem cell graft must be cleaned of malignant cells and contain cells that can fight against foreign substances with the immune system. Bone marrow stem cells are usually collected repeatedly from the back of the hip bone until a certain number of cells has been gathered. However, if sufficient cells cannot be obtained there, marrow may also be collected from the front of the hip bone or from the breastbone. The minimum number of marrow cells needed for long-term success in humans is not precisely known, but the amount of marrow cells collected generally varies depending on the diagnosis and the type and intensity of the pre-transplant conditioning.
What Is Allogeneic Bone Marrow Transplant?
Allogeneic bone marrow transplantation is a method used to restore normal blood production and treat diseases such as cancer. Through it, diseased bone marrow is replaced with healthy bone marrow from a donor. After transplantation, the cells travel to the patient's bone marrow and take the place of the patient's own stem cells. They then develop into all parts of the blood and immune system, including red blood cells, white blood cells and platelets. The new cells may be treated in the laboratory before they are transplanted. It is important to undergo chemotherapy and radiation therapy before transplantation. In this way, cancer cells are destroyed and some room is made in the bone marrow for the transplanted stem cells. At the same time, it becomes harder for the immune system to reject the new cells.
Stem cell transplantation can be obtained not only from bone marrow but also from various sources such as peripheral blood and umbilical cord blood. For this reason, the term "hematopoietic stem cell transplantation" has replaced the term "bone marrow transplant". Hematopoietic stem cells are given different names according to their source, that is, according to who they were obtained from. Stem cells obtained from the patient themselves are called autologous; cells taken from an identical twin are called syngeneic; and cells obtained from someone other than the patient or an identical twin are called allogeneic stem cells.
In Which Diseases Is Allogeneic Bone Marrow Transplant Used?
Allogeneic bone marrow transplant is mainly used in patients with cancer, but it is also a procedure used in the treatment of some diseases that cause bone marrow failure. The disorders for which allogeneic bone marrow transplant is preferred are:
Malignant Disorders
Acute myeloid leukemia
Acute lymphoblastic leukemia
Chronic myeloid leukemia
Myelodysplastic syndromes
Myeloproliferative disorders
Non-Hodgkin lymphoma
Hodgkin disease
Chronic lymphocytic leukemia
Multiple myeloma
Juvenile chronic myeloid leukemia
Non-Malignant Disorders
Aplastic anemia
Paroxysmal nocturnal hemoglobinuria
Fanconi anemia
Blackfan-Diamond anemia
Thalassemia major
Sickle cell anemia
Severe combined immunodeficiency
Wiskott-Aldrich syndrome
Inborn errors of metabolism
Who Is Allogeneic Bone Marrow Transplant Performed On?
Allogeneic bone marrow transplant is generally performed on patients who are at high risk and have conditions that require advanced treatment. This treatment is an effective method used in the treatment of many malignant and non-malignant hematologic diseases. Allogeneic bone marrow transplant is also preferred when donor cells need to be given to patients whose immune system is severely suppressed. For this procedure to be carried out, full HLA (human leukocyte antigen) compatibility between donor and recipient is required.
How Is the Donor Selected and What Is the Preparation Process?
Once it has been determined that an allogeneic bone marrow transplant is a necessary treatment for the patient, a search for a suitable donor begins. The donor may be a family member, a relative, or an unrelated person with no genetic similarity. Matching is important to increase the chance of transplant success.
Before the transplant, the patient receives conditioning treatment. This treatment consists of radiation and chemotherapy. Chemotherapy and radiation therapy are started shortly after admission to the hospital. In this way, the remaining cancer cells are destroyed and the immune system is suppressed. The aim is to weaken the immune system to prevent the donor cells from being rejected. This conditioning treatment enables the newly transplanted cells to travel through the bloodstream to the patient's bone marrow and grow there.
How Is the Transplant Procedure Carried Out?
The transplant of stem cells or bone marrow is performed 1-3 days after the last dose of chemotherapy and radiation. Sometimes the cells may be modified in the laboratory before transplantation. When no changes are made to the cells collected from the donor, it is called an unmodified transplant.
The first stage of the transplant procedure is the collection of bone marrow from the donor. Bone marrow is generally collected from the back of the hip area of the donor under anesthesia, by inserting a hollow needle. Pain may be felt in the area for about a week. Then, a transplant procedure similar to a simple blood transfusion is carried out.
What Is the Post-Transplant Process Like?
The new bone marrow does not recover immediately after it is transplanted. The stem cells of the new marrow travel to the bones and go through a growth process. After the transplant, the patient's treatment and follow-up must continue for at least 1 year.
What Are the Possible Complications After Transplant?
Some important complications that may be encountered after transplant are:
Rejection and Graft Failure: The transplanted cells may be destroyed by the patient's immune system, or the bone marrow cells may not function sufficiently. This generally occurs within the first 60 days after transplant, but it can also occur later.
Infections: Because of the immunosuppressive drugs used after transplant, patients are more vulnerable to infections. In particular, the risk of fungal and viral infections increases. Infection prevention measures are taken for this purpose.
Genitourinary Toxicities: High-dose chemotherapy before transplant can cause some urinary tract problems, especially hemorrhagic cystitis. This complication can be brought under control with appropriate medications and fluid therapy.
Liver Toxicities: Damage that occurs in the blood vessels of the liver after transplant may manifest with symptoms such as weight gain, abdominal pain and fluid accumulation. This condition is managed with appropriate treatment and certain medications.
Acute Graft-Versus-Host Disease (GVHD): Graft-Versus-Host disease occurs in about half of patients. This disease represents the most important barrier to allogeneic bone marrow transplant. Graft-Versus-Host disease is acute and generally appears within the first 100 days after transplant. The new cells may attack the patient's tissues. This disease can affect the skin, the gastrointestinal system and the liver. Its severity may vary, and it may need to be treated.
These complications are managed through pre-transplant risk assessments and careful care and follow-up after transplant.
Frequently Asked Questions
In autologous bone marrow transplant, the stem cells are taken from the patient who will receive the transplant. In other words, the patient is their own donor. Allogeneic transplantation, on the other hand, involves taking stem cells from a donor other than the patient. This donor may be a relative or an unrelated person. When selecting a donor for allogeneic bone marrow transplant, factors such as the type of disease, its condition and the urgency of finding a donor are taken into account. One of the most important considerations in donor selection is close tissue matching between the recipient and the donor in order to prevent graft rejection. Graft rejection occurs when the patient's immune system perceives the donor's cells as foreign and tries to destroy them. When the donor and recipient match well, graft rejection is rare. If a good match exists, the donor is informed about the transplant process. If, after being informed, the donor decides to donate, a consent form is signed; the donor is never forced, and the decision belongs entirely to them. Afterwards, examinations and some tests are carried out to make sure the donor's health is good.
To prepare the patient's body before transplant, conditioning treatment consisting of chemotherapy and radiation therapy is carried out. The purpose of this treatment is to kill the cancer cells remaining in the body and to make room for donor cells in the bone marrow spaces. The transplant process is also psychologically difficult for many patients, so the patient is prepared emotionally. An HLA blood test, bone marrow biopsy, full physical examination, computed tomography, electrocardiogram and other blood tests, complete blood count, and screening tests for viruses such as hepatitis B and HIV are performed.
After transplantation, there are very few risks for donors, and no serious complications are seen. Problems such as sore throat or nausea caused by anesthesia may occur. However, some complications and toxicities may appear in the first week. There is a possibility that the cancer may return. For this reason, post-transplant care and follow-up are important. During the transplant procedure, the patient is awake; this is not a painful procedure. Donor cells are given to the patient when they are ready. After the patient is discharged, they enter a recovery period lasting about a year. Weakness may be felt during the first few weeks. In allogeneic bone marrow transplants, graft-versus-host disease (GVHD) is a common complication. When the donor's immune cells perceive the patient's body as foreign, they may attack certain organs, usually the skin and liver. This condition increases the likelihood of infection. The disease is divided into acute and chronic types. The acute type begins immediately after transplantation and lasts a short time. The chronic type begins later and lasts a long time. Graft-versus-host disease is prevented by giving the patient drugs that suppress the immune system. Because immunosuppressive drugs are used after transplant, patients who undergo allogeneic stem cell transplantation are at greater risk of bacterial, fungal and viral infections than patients who undergo autologous stem cell transplantation. Prophylaxis is given routinely to prevent infections. Long-term follow-up and care after allogeneic bone marrow transplant require constant communication and coordination between the patient and the healthcare team. It is critically important for maintaining the patient's health and preventing complications. Because the patient needs to be examined by specialist doctors at regular intervals and certain tests need to be done, it is important not to miss routine check-ups. Attention should be paid to personal hygiene and to keeping the patient's home clean. Raw fruits and vegetables should be avoided, and foods should be washed carefully. To manage your recovery in the best way, it is important to have your health checks done regularly. If you experience any problem or have concerns after the transplant, it is recommended that you consult a specialist immediately.
