Bone Marrow and Stem-Cell Transplants
Bone marrow is the spongy tissue inside the large bones of the body that is responsible for all blood cell production: red blood cells, white blood cells and platelets. These cells are all developed from precursor (initiating) cells called stem cells, which can be found in the bone marrow and the circulating blood.
How do stem-cell transplants work?
As stem cells divide rapidly they are susceptible to chemotherapy and radiation therapy. Therefore, the doses of chemotherapy and radiation therapy used to treat lymphoma are limited due to the risk of damaging these stem cells. However, people with lymphomas that are difficult to treat or resistant to standard therapy may benefit from chemotherapy or radiation therapy given in very high doses (myeloablative therapy), but this can potentially destroy all the stem-cells in the bone marrow and leave the person at very high risk for infection.
To combat this problem, a person may receive a bone marrow transplant or a stem-cell transplant. This means that they receive stem cells (either their own stem cells that were stored prior to myeloablative therapy or stem cells from a donor) to replenish the bone marrow which has been destroyed by the high-dose therapy.
What is the difference between a bone marrow transplant and a stem-cell transplant?
There are two different types of transplants: bone marrow transplants (BMTs) and peripheral blood stem-cell transplants (PBSCTs). The difference between the two is where the stem cells are taken from. In BMTs, the stem cells are taken from the bone marrow; in PBSCTs, the stem cells are taken from the circulating blood.
PBSCTs are now performed more often than BMTs as the procedure is easier and the body is able to regenerate new stem cells faster.
Where do the transplanted stem cells come from?
Stem cells are transplanted into a person after myeloablative therapy (chemotherapy or radiation therapy that destroys the stem cells in the bone marrow).
The transplanted stem cells can come from two sources:
- Autologous stem cell transplant: the person themselves provides the stem cells before they receive the myeloablative (high dose) treatment
- Allogeneic stem cell transplant: the stem cells are provided by a compatible donor, such as a sibling
Autologous stem cell transplants are more commonly performed in the management of lymphoma as they are better tolerated by the person with cancer.
How are transplants performed?
Four steps are involved in a stem cell transplant (BMT or PBSCT):
1. Harvesting stem cells or bone marrow
- Harvesting is the procedure by which the bone marrow or stem cells are obtained in preparation for the transplant. In a BMT, the stem cells are withdrawn from the bone marrow by inserting a needle into a bone in the pelvic region (hip). The bone marrow is then filtered and stored until the day of the transplant.
- In a PBSCT, stem cells are taken from the bloodstream, a far easier and more commonly used option. The stem cells are separated from other components of the blood in a process called apheresis, and the rest of the blood is returned to the patient.
2. Processing/preserving the stem cells or bone marrow
- Stem cells or bone marrow harvested from the person (autologous transplant) are usually stored in a freezer until ready for use. Stem cells or bone marrow derived from a donor (allogeneic transplant) are usually collected immediately before use and not stored for any length of time.
3. Administering myeloablative therapy
- High-dose chemotherapy, with or without myeloablative radiation therapy, is then administered to the person to destroy the cancerous cells, as well as the healthy cells in the bone marrow.
4. Reinfusing harvested stem cells or bone marrow
- The harvested stem cells or bone marrow (obtained from either the person's own healthy cells or from a donor) are then transplanted intravenously into the person's bloodstream. The stem cells travel through the body to the bone marrow where they settle and begin to produce new, healthy blood cells.
- Eventually, they will produce enough healthy cells to repopulate the whole bone marrow, replenishing all blood and immune cells. In the period of time between the myeloablative therapy and the transplanted stem cells beginning to make new blood cells, the person is at an increased risk of infection and bleeding complications, and must be closely monitored.
Patient receiving stem cell transplant
What are the side effects of transplants?
Transplants are very strenuous procedures and take weeks or months to complete. They also take a large toll on the body. As such, they are not an option for everyone. Various factors, including age, medical history, type of lymphoma and response to previous therapies are considered.
A major risk associated with transplants is infection, due to the loss of immune function from the myeloablative therapy. Excessive bleeding is also a concern due to the loss of platelets (necessary for effective blood clotting). Both of these side effects are treatable, with antibiotics given to prevent infection and platelet transfusions to prevent bleeding. Transfusions of red blood cells may also be required to treat anaemia.
Some side effects of stem cell transplant are similar to those seen with chemotherapy and radiation therapy, such as nausea, vomiting, fatigue, loss of appetite, mouth sores, hair loss and skin reactions. These are mainly due to the side effects of the myeloablative therapy. Some long-term side effects of myeloablative therapy can include infertility (the inability to have children), cataracts (a clouding of the lens of the eye that can result in decreased vision), and damage to various organs including the liver, kidneys, lungs and heart, and the potential for a new cancer to develop.
A complication called graft-versus-host disease (GVHD) can occur with allogeneic transplants. The immune cells from the donated tissue (called the graft) can react against the cells of the person who received the transplant (the host) and attack them. This can cause damage to the person's organs, including skin, liver and digestive tract. This reaction can occur within a few weeks of the transplant procedure (called acute GVHD), or much later (called chronic GVHD). GVHD can be serious and difficult to treat. Doctors commonly try to prevent it ahead of time using medications and specific procedures that can reduce the immune reaction of the donor and the recipient.
What happens after treatment?
When your treatment is completed you will continue to have follow-up appointments with your specialist doctor. Usually these are quite regular (monthly) to start with but, if remission continues, they will decrease in frequency to 6 monthly appointments and then once a year.
Follow-up appointments can be difficult due to the worry of the disease relapsing but these appointments are an important part of your care - it allows the doctor to assess your progress and it gives you the opportunity to talk about any concerns you may have. If you are worried about anything or experience any change in how you are feeling in between these appointments, you should call your doctor and bring your appointment forward.'
It is also important to have regular contact with your general practitioner (GP) as he or she can offer support and advice on a more regular basis, if needed. Monitoring your general health and staying fit and well should be an ongoing commitment for everyone - it is our most precious asset!
From The DVD - "Your Journey of Lymphoma Treatments"
Related video: Chapter 7 - Stem Cell Harvest
From The DVD - "Your Journey of Lymphoma Treatments"
Related video : Chapter 8 - Stem Cell Transplant