A stem cell transplant is sometimes used to treat childhood leukemia. Stem cells are basic cells that develop into different types of cells that have different jobs. For example, we have different types of blood cells and they all develop from blood stem cells.
A stem cell transplant replaces a child’s stem cells. It allows the healthcare team to give very high doses of chemotherapy and radiation therapy to kill leukemia cells, or blasts, and then replace the stem cells with new ones from a donor. These donor stem cells also help fight leukemia because they will have an immune response to the leukemia cells.
At one time, the bone marrow was the most common source of stem cells for transplant. Now blood is used more often as the source of stem cells. Another source of stem cells is umbilical cord blood.
Stem cell transplants may be considered for children with leukemia in the following situations.
Children with subtypes of AML that have a high risk of recurrence (high-risk AML) may be given a stem cell transplant right after they go into remission. Children with other subtypes that have a lower risk of recurrence (low-risk AML) may be given a stem cell transplant only if there is a recurrence after second complete remission.
Stem cell transplant may be used when ALL doesn’t respond well to treatment or has recurred early after it goes into remission. Stem cell transplant may also be given when ALL is in remission but has a high risk of relapsing.
Stem cell transplant may be used after first remission of rarer forms of ALL, such as:
Allogeneic stem cell transplant is the most common type used with childhood leukemia. In this type of transplant, the stem cells are taken from one person (the donor) and are given to another person (the recipient). The donor may be a relative or may be unrelated to the recipient. The donor and recipient are matched through a process called human leukocyte antigen (HLA) typing.
A stem cell transplant is a very risky and complex procedure. For this reason, stem cell transplants are done in specialized transplant centres or hospitals by a team of highly trained healthcare professionals.
The day the stem cells are given is usually referred to as Day 0. The days after transplant are numbered upward (for example, Day 1, Day 2 and so on). This system is useful to describe the timing of events, such as when new blood cells begin to appear (engraftment) or complications of the procedure.
There are 3 stages in a stem cell transplant procedure.
Before the stem cell transplant, some procedures are done to check that the recipient is a good candidate. Once a donor is found that is a good match, stem cells are collected for the transplant (called harvesting).
The stem cell transplant procedure has 2 steps. Conditioning, or intensive, therapy is the first step. High-dose chemotherapy is given alone or with radiation therapy. The chemotherapy is used to “condition” the child’s bone marrow to accept donor stem cells. It also destroys the bone marrow to make room for new stem cells.
The second step is giving the stem cells. The stem cells are given, or infused, to the child through a central venous cathetercentral venous catheterA catheter (flexible tube) that is passed through a vein in the neck, groin or chest into the vena cava (the large vein leading into the heart)., similar to a blood transfusion. They are usually given over 1–2 hours.
A child is watched closely after a stem cell transplant. For the first 3–4 weeks after transplant, the child is at high risk for serious infections and bleeding because of low white blood cell and platelet counts. Blood and platelet transfusions and antibiotics may be given to prevent or treat infections and bleeding problems.
The child is closely followed up for the first year and beyond if there are complications. It may take several months to fully recover after a stem cell transplant.