Stem cell transplant

A stem cell transplant replaces stem cells. It is used when stem cells or bone marrow have been damaged or destroyed by disease, including some types of cancer, or by high doses of chemotherapy or radiation therapy used to treat cancer.

Bone marrow is the soft, spongy tissue inside your large bones. The bone marrow’s main job is to make blood cells that flow through the body. Stem cells are the most basic cells in the bone marrow, and they develop into different types of blood cells. There are 2 major types of stem cell transplant – allogeneic and autologous. In an allogeneic stem cell transplant, stem cells are removed from another person (a donor) and given to you (the recipient). In an autologous stem cell transplant, you provide your own stem cells. If you receive stem cells from your identical twin, this is called a syngeneic transplant.

A stem cell transplant is also called:

• a bone marrow transplant – when the stem cells are taken from the bone marrow
• a peripheral blood stem cell transplant (PBSCT) – when the stem cells are taken from the blood
• a blood cell transplant (BCT)
• a hematopoietic stem cell transplant (HSCT)
• a high-dose therapy with stem cell rescue

Most stem cells are found in the bone marrow. The stem cells in the bone marrow turn into red blood cells, white blood cells and platelets. When these blood cells mature they move into the peripheral blood (the blood that flows through the body). If the bone marrow is damaged or destroyed, it can’t make normal blood cells. In a stem cell transplant, healthy stem cells are placed in your body to help your bone marrow start to work properly. The new stem cells make healthy blood cells.

A stem cell transplant may be used to treat some cancers such as leukemia, lymphoma, multiple myeloma and neuroblastoma. It may also be used after high-dose radiation and chemotherapy to treat the cancer.

Doctors consider some important factors before deciding to treat cancer with a stem cell transplant, including:

• your age – younger people often cope better with stem cell transplants and have fewer complications. Some transplant centres set upper age limits, but this may depend on your general health and other factors
• your overall health and other medical conditions
• the characteristics of your cancer – such as the type and stage of the cancer, whether you are in remission or have had a relapse, the chance of relapse after transplant and how sensitive the cancer is to chemotherapy

The type of transplant is based on who gives the stem cells.

Autologous transplants use stem cells from your own bone marrow or blood.

A double autologous (tandem) transplant means that you receive 2 autologous transplants. Before each one, you are given high-dose chemotherapy. Your stem cells for both transplants are usually collected before the first course of chemotherapy. The second transplant is usually done between several weeks and 6 months after the first.

Allogeneic transplants use stem cells from someone else. The donor may be a relative or someone who is not related to you.

A mini-transplant means that lower doses of chemotherapy and radiation are given before an allogeneic transplant. This may be useful for older people and those with other health problems who may not be able to handle a standard transplant and the side effects. A mini-transplant is also called a reduced intensity transplant or non-myeloablative transplant.

Syngeneic transplants use stem cells from an identical twin.

The process of collecting or removing stem cells is called harvesting. The stem cells can come from the bone marrow, the peripheral blood or the umbilical cord (from a newborn baby).

For autologous transplants, the stem cells are usually collected when the person is in remission and has recovered from other treatments.

Bone marrow is most often taken from the pelvic bones because they have the most bone marrow and a large supply of stem cells.

Removing stem cells from the bone marrow is usually done using a general anesthetic (you will be asleep) in the operating room. A large needle is put into the back of the hip bone. Bone marrow is pulled out through the needle. This is repeated until enough marrow has been collected for the transplant. It usually takes 1 to 2 hours.

A dressing is put on where the needle went in, and you will recover from the anesthetic in the recovery room. The hip area may be sore for a few days. Medicines can be taken to relieve pain. The body usually replaces the collected stem cells within a few weeks.

The cells are filtered to remove bone fragments and fat particles, stored in special solution bags and frozen until they are needed for the transplant.

Blood does not normally have many stem cells. Growth factors, such as G-CSF or plerixafor, may be given for a few days to stimulate stem cells to grow faster and move into the blood from the bone marrow.

Removing stem cells from the blood is done through an IV (intravenous) line. An IV is placed in a large vein in the donor’s arm. The IV tubing is attached to a machine that separates and collects stem cells from the blood. After the stem cells are removed, the blood is returned to the donor. The process takes several hours and may need to be repeated once a day for a few days to collect enough stem cells for a transplant.

The collected stem cells are filtered, stored in bags and frozen until they are needed for a transplant.

The blood of newborn babies normally has a large number of stem cells. After birth, the blood that’s left behind in the placenta and umbilical cord can be collected. Blood is collected from the umbilical cord shortly after a baby is born. A machine separates and collects stem cells from the cord blood.

The number of stem cells that needs to be collected from an umbilical cord is less than what needs to be taken from adult bone marrow. This is because more blood cells can be formed from each cord blood stem cell than from each adult bone marrow stem cell. The stem cells are filtered, put in bags and frozen.

Some cord blood banks store the stem cells until the family needs them (private use). Other places store cord blood to be used in people who are unrelated (public use).

Healthy parents who are expecting a baby can donate their child’s cord blood. To be eligible to donate, parents usually have to register with the cord blood bank when they are pregnant. Blood screening tests may be done on the mother before collection.

A cord blood donation may not be accepted if there are certain illnesses that run in the family or that have happened during or before the pregnancy that could be transmitted by a cord blood transplant.

Some private cord blood banks may charge collection and storage fees.

To improve the chance of a successful stem cell transplant, the donor’s stem cells need to match the recipient’s as closely as possible. A process called HLA (human leukocyte antigen) testing makes sure that the donor and recipient are closely matched. There are thousands of different combinations of possible HLA tissue types so it can be hard to find an exact match. But a transplant may still be done if the match is less than perfect.

Most matches are between close family members. The search for a donor starts with the recipient’s brothers and sisters because siblings have the greatest chance of being a match. If a match is not found within the family, the search starts for an unrelated donor through the Canadian Blood Services stem cell registry. It might seem unlikely, but it’s possible to find a good match with someone who is not a relative.

If a donor is found to be a good match, a medical exam and blood tests are done to make sure the donor is in good health. The transplant doctor identifies potential matches and arranges donor testing.

Find out more about HLA testing.