If you or a loved one will be having a bone marrow transplant or donating stem cells, what does it entail? What are the different types of bone marrow transplants and what is the experience like for both the donor and recipient?

A bone marrow transplant is a procedure in which when special cells (called stem cells) are removed from the bone marrow or peripheral blood, filtered and given back either to the same person or to another person.

Since we now derive most stem cells needed from the blood rather than the bone marrow, a bone marrow transplant is now more commonly referred to as stem cell transplant.

Bone marrow is found in larger bones in the body such as the pelvic bones. This bone marrow is the manufacturing site for stem cells. Stem cells are "pluripotential" meaning that the cells are the precursor cells which can evolve into the different types of blood cells, such as white blood cells, red blood cells, and platelets.

If something is wrong with the bone marrow or the production of blood cells is decreased, a person can become very ill or die. In conditions such as aplastic anemia, the bone marrow stops producing blood cells needed for the body. In diseases such as leukemia, the bone marrow produces abnormal blood cells.

The purpose of a bone marrow transplant is thus to replace cells not being produced or replace unhealthy stem cells with healthy ones.

This can be used to treat or even cure the disease.

In addition for leukemias, lymphomas, and aplastic anemia, stem cell transplants are being evaluated for many disorders, ranging from solid tumors to other non-malignant disorders of the bone marrow, to multiple sclerosis.

There are two primary types of bone marrow transplants, autologous and allogeneic transplants.

The Greek prefix "auto" means "self." In an autologous transplant, the donor is the person who will also receive the transplant. This procedure, also known as a "rescue transplant" involves removing your stem cells and freezing them. You then receive high dose chemotherapy followed by infusion of the thawed out frozen stem cells. It may be used to treat leukemias, lymphomas, or multiple myeloma.

The Greek prefix "allo" means "different" or "other." In an allogeneic bone marrow transplant, the donor is another person who has a genetic tissue type similar to the person needing the transplant. Because tissue types are inherited, similar to hair color or eye color, it is more likely that you will find a suitable donor in a family member, especially a sibling. Unfortunately, this occurs only 25 to 30 percent of the time.

If a family member does not match the recipient, the National Marrow Donor Program Registry database can be searched for an unrelated individual whose tissue type is a close match. It is more likely that a donor who comes from the same racial or ethnic group as the recipient will have the same tissue traits.

Learn more about finding a donor for a stem cell transplant.

Bone marrow cells can be obtained in three primary ways. These include:

The majority of stem cell transplants are done using PBSC collected by apheresis (peripheral blood stem cell transplants.) This method appears to provide better results for both the donor and recipient. There still may be situations in which a traditional bone marrow harvest is done.

Donating stem cells or bone marrow is fairly easy. In most cases, a donation is made using circulating stem cells (PBSC) collected by apheresis. First, the donor receives injections of a medication for several days that causes stem cells to move out of the bone marrow and into the blood. For the stem cell collection, the donor is connected to a machine by a needle inserted in the vein (like for donating blood.) Blood is taken from the vein, filtered by the machine to collect the stem cells, then returned back to the donor through a needle in the other arm. There is almost no need for a recovery time with this procedure.

If stem cells are collected by bone marrow harvest (much less likely,) the donor will go to the operating room and while asleep under anesthesia, a needle will be inserted into either the hip or the breastbone to take out some bone marrow. After awakening, there may be some pain where the needle was inserted.

A bone marrow transplant can be a very challenging procedure for the recipient.

The first step is usually receiving high doses of chemotherapy and/or radiation to eliminate whatever bone marrow is present. For example, with leukemia, it is first important to remove all of the abnormal bone marrow cells.

Once a person's original bone marrow is destroyed, the new stem cells are injected intravenously, similar to a blood transfusion. The stem cells then find their way to the bone and start to grow and produce more cells (called engraftment.)

There are many potential complications. The most critical time is usually when the bone marrow is destroyed so that few blood cells remain. Destruction of the bone marrow results in greatly reduced numbers of all of the types of blood cells (pancytopenia.) Without white blood cells there is a serious risk of infection, and infection precautions are used in the hospital (isolation.) Low levels of red blood cells (anemia) often require blood transfusions while waiting for the new stem cells to begin growing. Low levels of platelets (thrombocytopenia) in the blood can lead to internal bleeding.

A common complication affecting 40 to 80 percent of recipients is graft versus host disease. This occurs when white blood cells (T cells) in the donated cells (graft) attack tissues in the recipient (the host,) and can be life-threatening.

An alternative approach referred to as a non-myeloablative bone marrow transplant or "mini-bone marrow transplant" is somewhat different. In this procedure, lower doses of chemotherapy are given that do not completely wipe out or "ablate" the bone marrow as in a typical bone marrow transplant. This approach may be used for someone who is older or otherwise might not tolerate the traditional procedure. In this case, the transplant works differently to treat the disease as well. Instead of replacing the bone marrow, the donated marrow can attack cancerous cells left in the body in a process referred to as "graft versus malignancy."

If you'd like to become a volunteer donor, the process is straightforward and simple. Anyone between the ages of 18 and 60 and in good health can become a donor. There is a form to fill out and a blood sample to give; you can find all the information you need at the National Marrow Donor Program Web site. You can join a donor drive in your area or go to a local Donor Center to have the blood test done.

When a person volunteers to be a donor, his or her particular blood tissue traits, as determined by a special blood test (histocompatibility antigen test,) are recorded in the Registry. This "tissue typing" is different from a person's A, B, or O blood type. The Registry record also contains contact information for the donor, should a tissue type match be made.

Bone marrow transplants can be either autologous (from yourself) or allogeneic (from another person.) Stem cells are obtained either from peripheral blood, a bone marrow harvest or from cord blood that is saved at birth.

For a donor, the process is relatively easy. For the recipient, it can be a long and difficult process, especially when high doses of chemotherapy are needed to eliminate bone marrow. Complications are common and can include infections, bleeding, and graft versus host disease among others.

That said, bone marrow transplants can treat and even cure some diseases which had previously been almost uniformly fatal. While finding a donor was more challenging in the past, the National Marrow Donor Program has expanded such that many people without a compatible family member are now able to have a bone marrow/stem cell transplant.

Sources:

American Society of Clinical Oncology. Cancer.Net. What is a Stem Cell Transplant (Bone Marrow Transplant)? Updated 01/16. http://www.cancer.net/navigating-cancer-care/how-cancer-treated/bone-marrowstem-cell-transplantation/what-stem-cell-transplant-bone-marrow-transplant

U.S. National Library of Medicine. MedlinePlus. Bone Marrow Transplant. Updated 10/03/17. https://medlineplus.gov/ency/article/003009.htm

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