Patient education: Allogeneic bone marrow transplant (The Basics)

What is a bone marrow transplant? — A bone marrow transplant is a procedure that replaces abnormal or missing cells in the bone marrow with healthy cells. The bone marrow is the tissue in the center of certain bones. Normally, bone marrow makes blood cells, which the body needs to work normally. There are different types of blood cells, and all of them are made from cells in bone marrow called "hematopoietic stem cells."

If the bone marrow does not work normally, it can't make the blood cells that a person's body needs. To treat this, a doctor can put healthy stem cells, called "donor" cells, into the bone marrow. The donor cells can then make normal blood cells. A bone marrow transplant is also called a "stem cell transplant" or "hematopoietic stem cell transplant."

Why might I have a bone marrow transplant? — You might have a bone marrow transplant to help treat some kinds of cancer, such as leukemia or lymphoma, or another medical condition that affects your bone marrow.

What does "allogeneic" mean? — This means that the healthy stem cells come from another person. ("Allo" means "other.") Doctors use a process called "HLA typing" to find a donor who is a match for you. The donor cells might come from a relative, an unrelated person, or a newborn baby's umbilical cord.

In another type of bone marrow transplant, called "autologous" transplant, the donor cells come from your own body.

The right type of bone marrow transplant for you depends on many different things, including:

●What kind of cancer or other medical problem you have

●Your other health conditions

●Your age

●Your preferences

An advantage of allogeneic transplant is that the donor stem cells are slightly different from your own body's cells. This is true even if the person who donated the cells is found to be a "perfect" HLA match. (The exception is if you have an identical twin who donates stem cells. In this case, the cells would match yours exactly.) Because of the differences, the donor cells can attack your unhealthy cells. This is called the "graft-versus-tumor effect," and is an important part of how well the transplant works. But the donor cells can also sometimes attack your healthy organs, which can lead to problems. This is described more below. (See 'What are the side effects of a bone marrow transplant?' below.)

Your doctor can help you understand the risks and benefits of each type of transplant.

How do I find a stem cell donor? — Your doctors will talk to you about your options. If you have siblings, they might be tested to find out if any of them is a "match" for you. This involves special tests to look at certain proteins on their cells. This is called "HLA typing." HLA type is not the same as blood type (A, B, AB, or O).

There is about a 1 in 4 chance that a brother or sister will be a match for HLA type. If you have a sibling who is a match and is willing to donate stem cells, that is usually the best option. That's because siblings share similar genes, so a brother or sister's stem cells are more likely to work well with your body.

If no sibling is a good match, other options include:

●A donor who is not related to you – Doctors can find a match by searching registries. Registries are lists of people all over the world who have volunteered to donate stem cells.

●A parent or child – Your parents or children might have blood that half matches yours.

●Umbilical cord blood – Some parents choose to donate their baby's umbilical cord blood after birth. This blood contains stem cells that can be used in transplants. Doctors can also search cord blood registries for a match.

Before a person can donate stem cells, they need to:

●Get a physical exam and blood tests

●Answer questions, including about any medical problems they have had, medicines they have taken, and past vaccinations

●Learn about the risks related to donating stem cells

●Sign forms saying that they agree to be a donor

If your sibling or relative is donating stem cells, they will go to the hospital or transplant center for the procedure. Stem cells can be collected from the person's blood or bone marrow. After they donate, their body will create more stem cells to replace the ones that were removed.

What will happen before my transplant? — Your doctor will do an exam and tests. They will talk with you and your family about what to expect during and after the procedure.

Your doctor will put a thin tube into a blood vessel in your upper chest. This tube, called a "central line," will stay in place during your hospital stay. Your doctor will use it to give you treatments, as well as take blood for tests.

Just before your transplant, you will get "conditioning" treatment. This kills cancer cells and prepares your bone marrow to receive the donor stem cells. Conditioning treatment involves chemotherapy, radiation therapy, or both. When given at high doses, it is called "myeloablative conditioning." In some cases, your doctor might suggest a "mini-transplant" instead. This involves lower doses or other types of conditioning treatment. Your doctor will talk to you about the differences between the types of conditioning therapy.

What will happen during my transplant? — Soon after the conditioning treatment, your doctor will put the donor cells into your body through your central line or another vein. The stem cells will find their way to your bone marrow. There, they can start making normal blood cells.

What will happen after my transplant? — Most people need to stay in the hospital for several weeks after an allogeneic bone marrow transplant.

Right after a bone marrow transplant, your body has a higher chance than usual of getting an infection. Because of this, you will need to stay in a special hospital room and get certain medicines.

Your doctor might give you other treatments, depending on your symptoms. They will also do blood tests regularly to check that your bone marrow transplant is working properly.

Once your bone marrow is working normally and you go home, you will need to see your doctor for regular follow-ups.

What are the side effects of a bone marrow transplant? — The side effects depend on where your donor cells came from, as well as which treatments you have before the transplant.

After an allogeneic bone marrow transplant, the most common short-term side effects include:

●Mouth sores and diarrhea

●Nausea and vomiting

●Hair loss

●Lung, liver, or bone problems

●A condition called "graft-versus-host disease" ("GVHD") – In GVHD, the donor cells can attack organs in your body. This can cause a skin rash, diarrhea, and liver problems.

People can also have long-term side effects that include:

●Trouble getting pregnant – If you want to have a baby in the future, talk with your doctor before your bone marrow transplant.

●Other cancers that can happen years later

●Chronic (long-lasting) GVHD

More on this topic

Patient education: Neutropenia and fever in people being treated for cancer (The Basics)
Patient education: Donating bone marrow or blood stem cells (The Basics)
Patient education: Autologous bone marrow transplant (The Basics)

Patient education: Hematopoietic cell transplantation (bone marrow transplantation) (Beyond the Basics)