A stem cell transplant may be used to treat chronic myelogenous leukemia (CML).
A stem cell transplant replaces a person's stem cells. It is used to restore bone marrow when it has been damaged by disease or destroyed by high doses of chemotherapy or radiation therapy. A stem cell transplant may also be called a bone marrow transplant.
Stem cells are the basic cells from which all our blood cells develop. They are found in the bone marrow and blood.
At one time, the bone marrow was the most common source of stem cells for transplant (bone marrow transplant). Now blood is being used more often as the source of stem cells (peripheral stem cell transplant).
Stem cell transplants may be considered for people with CML in the following cases:
- as first-line therapy for selected people in the chronic phase
- should be considered for people under the age of 30 years
- in the accelerated and blast phases for younger people
- less successful than when used in the chronic phase, but can produce remission in some people
- during relapse following treatment with imatinib (Gleevec) or interferon alfa (Intron A, Roferon A)
Types of transplants
There are 3 basic types of stem cell transplants. The main type of stem cell transplant used with CML is the allogeneic transplant.
The stem cells are taken from one person (donor) and are given to another person receiving the transplant (recipient). A donor may be a relative or an unrelated person. The donor and recipient are matched through a process called HLA typing.
- Allogeneic stem cell transplant is the only treatment known to cure CML.
- Because targeted therapies now treat CML more effectively, doctors and researchers are not sure when a stem cell transplant should be done and there are no definite guidelines in place at this time.
Reduced-intensity allogeneic transplant
Reduced-intensity allogeneic transplant is also called non-myeloablative transplant and mini-transplant. This approach uses less intense chemotherapy or radiation to prepare for the transplant than a standard allogeneic transplant. Therefore, it may be useful in older people who may not tolerate a standard transplant.
The stem cells are taken from the person's own bone marrow or blood. An autologous transplant is sometimes used to try to return CML to the chronic phase, but it is unlikely to cure the cancer.
The stem cells are taken from a donor who is the identical twin of the recipient. Very few people have an identical twin so this type of transplant is very rare.
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. Stem cells are collected for the transplant (called harvesting).
The stem cell transplant procedure has 2 steps:
- conditioning, or intensive, therapy – High-dose chemotherapy, with or without radiation therapy, is given to:
- "condition" the person's bone marrow to accept donor stem cells (allogeneic transplant)
- remove any remaining cancer cells in the body (autologous transplant)
- destroy the bone marrow and make room for new stem cells
- giving the stem cells – The stem cells are given (infused) to the person over 1–2 hours through a central venous catheter, similar to a blood transfusion
A person is watched closely after a stem cell transplant. They are also carefully followed up for a period of time after leaving the hospital. It may take several months to fully recover after a stem cell transplant.
Donor lymphocyte infusion
A donor lymphocyte infusion (DLI) may be given if CML relapses after an allogeneic stem cell transplant.
- The lymphocytes are usually from the original stem cell donor.
- DLI may cause a more intense immune reaction against the CML cells.
- It brings about long-term remissions in more than half the people who relapse following allogeneic stem cell transplant.
See a list of questions to ask your doctor about stem cell transplant.