What is Bone Marrow Transplant
Bone marrow transplant is a type of treatment for some diseases that affect the blood cells, such as leukemias and lymphomas. Additionally, it is used in other conditions unrelated to cancer, such as severe aplastic anemia (characterized by a lack of blood cell production in the bone marrow), Fanconi anemia, and sickle cell anemia.
This process involves replacing diseased or deficient bone marrow with normal bone marrow cells. The goal is to reconstitute the marrow, making it healthy and functional again.
What is bone marrow?
Bone marrow is a liquid-gelatinous tissue that occupies the interior of bones. It plays a central role in the development of blood cells, as it contains hematopoietic stem cells that produce the components of blood: white blood cells (leukocytes), red blood cells (erythrocytes), and platelets.
White blood cells are the most important agents of the immune system, protecting against infections. Red blood cells transport oxygen from the lungs to cells throughout the body and carry carbon dioxide from the cells back to the lungs to be exhaled. Finally, platelets are involved in the blood clotting system.
Types of Bone Marrow Transplants
Autologous or Autogeneic Transplant: The bone marrow precursor cells (bone marrow or peripheral blood cells) are from the individual being transplanted (recipient). They are collected and frozen for later use.
This type of transplant is usually chosen for the treatment of diseases that do not affect the quality of the bone marrow (i.e., those that do not originate directly in the marrow) or when the disease has already diminished to the point of no longer being detected (remission state).
Some examples include:
- Acute Myeloid Leukemia;
- Non-Hodgkin Lymphoma;
- Chemotherapy-sensitive Hodgkin’s Disease;
- Multiple Myeloma;
- Germ Cell Tumor; and
- Neuroblastoma.
The bone marrow precursor cells come from another individual (donor), according to the level of compatibility of the blood material.
Allogeneic transplant
The first option is always for the marrow of a sibling. If the recipient (patient) does not have a sibling or if the sibling is not a match, compatibility is checked with the mother and father. If there is no related donor with compatibility, a compatible unrelated donor is sought in bone marrow registries.
The marrow precursor cells come from another individual (donor), according to the level of compatibility of the blood material. The first option is the marrow of a donor who is a blood relative, preferably a sibling.
In the absence of a compatible sibling or if compatibility cannot be found, the investigation extends to the parents, seeking compatibility with the recipient’s (patient’s) mother and father.
Still, if there is no availability of a related donor with compatibility, the search is directed to bone marrow registry records in search of a compatible unrelated donor.
The indications for an allogeneic related bone marrow transplant are:
- Acute myeloid leukemia;
- Acute lymphoid leukemia / lymphoblastic lymphoma;
- Ph+ acute lymphoid leukemia;
- Chronic myeloid leukemia;
- Acquired or constitutional severe aplastic anemia;
- Myelodysplastic syndrome, including chronic myelomonocytic leukemia;
- Primary cell immunodeficiency;
- Thalassemia;
- Evolutionary-phase primary myelofibrosis;
- Chronic lymphocytic leukemia;
- Multiple myeloma;
- Indolent non-Hodgkin lymphoma; and
- Chemotherapy-sensitive Hodgkin’s disease.
Allogeneic related peripheral blood stem cell transplant:
- Acute myeloid leukemia;
- Acute lymphoblastic leukemia / lymphoblastic lymphoma;
- Ph+ acute lymphoblastic leukemia;
- Chronic myeloid leukemia;
- Myelodysplastic syndrome, including chronic myelomonocytic leukemia;
- Thalassemia;
- Evolutionary phase of primary myelofibrosis;
- Chronic lymphocytic leukemia;
- Multiple myeloma;
- Indolent non-Hodgkin lymphoma; and
- Chemotherapy-sensitive Hodgkin’s disease.
Transplant of bone marrow precursor cells obtained from umbilical cord blood.
Umbilical cord stem cells are used. The main advantage is that the cells are immediately available, meaning there is no need to locate the donor and undergo bone marrow extraction. Additionally, complete compatibility between the cord blood and the patient is not required.
However, there are also drawbacks. The main one is the dose limitation, as the donation occurs in a single collection (with no possibility of a second collection) shortly after birth, and the volume is limited – hence, the number of stem cells may be restricted.
Therefore, there is a weight limit for the patient based on the amount of stem cells collected from the cord blood: the patient must weigh between 50kg and 60kg. The good news is that it is currently possible to use a technique to combine two cords for the same patient, allowing for use in adults with higher weight.
The main indications for this type of transplant are:
- Acute myeloid leukemia;
- Acute lymphoblastic leukemia / lymphoblastic lymphoma;
- Ph+ acute lymphoblastic leukemia;
- Chronic myeloid leukemia;
- Myelodysplastic syndrome, including chronic myelomonocytic leukemia;
- Thalassemia;
- Evolutionary phase of primary myelofibrosis;
- Chronic lymphocytic leukemia;
- Multiple myeloma;
- Indolent non-Hodgkin lymphoma; and
- Chemotherapy-sensitive Hodgkin’s disease.
How bone marrow transplantation is performed
Firstly, specific compatibility tests are conducted. Samples of the recipient’s and donor’s blood are analyzed to verify if there is complete compatibility between them, which minimizes the risk of the marrow being rejected by the recipient.
When there is compatibility, the donor undergoes a procedure in the operating room, under anesthesia, lasting approximately two hours. It involves multiple needle punctures into the posterior bones of the pelvis and aspiration of the marrow. There is no harm or compromise to the donor’s health.
As for the recipient, before receiving the transplant, they need to undergo a treatment that attacks the diseased cells and destroys their own marrow. Once this is done, they will receive the healthy marrow in a relatively simple process, similar to a blood transfusion. As the cells from the new marrow circulate through the bloodstream, they lodge in the bone marrow, where they develop.
How to identify the effectiveness of bone marrow transplant?
- The patient’s blood count is normal. This means that the count of red blood cells, white blood cells, and platelets is within the expected values for a healthy individual. It is important to note that, shortly after the transplant (two weeks later), it is expected that these values will drop to very low levels, affecting the immune system and making the patient more prone to opportunistic infections, bleeding, and fatigue.
To avoid these complications, the medical team may choose to administer blood and platelet transfusions, as well as antibiotics. As the new stem cells begin to multiply, more red blood cells are formed. As a result, the blood count normalizes, indicating that the transplant was successful; and
- The cancer is under control. The cure of cancer is usually the primary goal of a bone marrow transplant. And it can be possible in some cases, such as certain types of leukemia or lymphoma. For other diseases, cancer remission may be the best achievable outcome. This means not having any signs or symptoms of neoplasia.
Possible side effects and complications
The main risks for the patient are related to infections and the chemotherapy used during treatment. As the marrow recovers, its new cells grow with a new “memory.”
Since these are defense cells of the body, they may recognize some organs of the individual as foreign. This complication, called graft-versus-host disease, is relatively common, of varying intensity, and can be controlled with appropriate medication.
In bone marrow transplantation, rejection is relatively rare but can occur. That is why the analysis and selection of the donor and the prior preparation of the patient are so important.
The risks for those who donate bone marrow are minimal. A few weeks after the aspiration procedure, the bone marrow will be fully recovered.
The symptoms that may occur after donation are local pain, asthenia (temporary weakness), and headache. In general, these are temporary symptoms and easily controlled with simple medications, such as painkillers.
