What Goes into a Stem Cell Transplant?
Stem cells have a remarkable capability to divide persistently and differentiate into different types of cells present in our body. From red blood cells, white blood cells and platelets to bone, cartilage, fibrous connective tissue, and fat, stem cells have the ability to form each and every type of cell present in the body. Although stem cells can be produced in other ways, in adults, bone marrow is the primary source of stem cells.
At times, certain cancers, diseases or disorders can cause bone marrow to stop performing thir normal functions. As a result, adequate numbers of healthy stem cells are not released into the body thereby preventing the formation and production of new and healthy blood cells. With the loss of healthy blood cells comes the body’s inability to protect itself from various types of infections and diseases. In such a scenario, a stem cell transplant becomes essential.
What is Stem Cell Transplant?
Stem cell transplant is an intricate procedure in which healthy stem cells are infused into the body to replace damaged stem cells. Before introducing the healthy stem cells, the patient is given high dose chemotherapy to destroy all the diseased, as well as normal blood-producing, stem cells in the bone marrow.
When the new stem cells are introduced into the body of the patient, they travel all the way to the bone marrow via the blood stream and replace the destroyed stem cells. Gradually, these new stem cells start dividing and differentiating into different types of body cells, helping to rebuild a healthy immune system.
Where Do the Stem Cells for Stem Cell Transplant Come From?
Stem cells for stem cell transplant come from four primary sources:
- Umbilical Cord Blood: Until recently, the umbilical cord was considered to be waste material and was discarded soon after birth. Nowadays, many parents choose to drain their newborns umbilical cord blood in order to preserve the valuable cord blood stem cells that are contained within this blood.
Obtaining stem cells from the umbilical cord poses no risk either to the child or the mother. When a parent decides to bank her child’s cord blood, she generally has two options: to preserve the stem cells at a private bank for the family’s own use or to donate the cord blood stem cells to a public bank, where the stem cells may be used for research or given to a patient who requires it urgently.
- Bone Marrow: For harvesting the stem cells from the bone marrow, the donor is given anaesthesia (general or local) and the marrow is drawn out of the hipbone or breastbone through a needle. The entire process takes about one hour. However, it does require that the donor be hospitalized for a few days.
There are no major risks associated with bone marrow donation except the common uncertainties related to anaesthesia. There may be some stiffness or soreness in the area from where the bone marrow has been extracted. For a few weeks the donor may feel tired. The recovery period varies from a few days to three to four weeks.
- Peripheral Blood: For retrieval of stem cells from the peripheral blood, the donor is first administered medications for about four to five days to increase the number of stem cells in his blood. Next, a process known as apheresis, whereby blood is drained from a vein in the arm, is performed. The withdrawn blood goes into a machine where the stem cells are removed. The blood then flows back into the donor minus the removed stem cells. Apheresis requires one to three session, lasting approximately four to six hours each, in order to collect enough stem cells.
For the extraction of stem cells from the peripheral blood, no anaesthesia is given to the donor, therefore the donor is not exposed to any risks arising from anaesthesia. However the medications given to increase the number of stem cells may produce side effects including nausea, headache, fatigue, muscle and bone pain, and difficulties sleeping. These automatically disappear within two to three days of the last dose of medication.
- Embryo: The fourth source of stem cells is the embryo. For the extraction of these stem cells, an egg is fertilized in vitro. When the fertilized egg has developed for four to five days (the blastocyst stage), the stem cells are retrieved.
Although stem cells derived from embryos have a greater capacity than any other type of stem cell to differentiate into other types of body cells, due to ethical reasons, this source of stem cells is seldom used.
What are the Different Types of Stem Cell Transplant?
Stem cell transplant can be divided into three types:
- Autologous stem cell transplant, in which healthy stem cells are retrieved from the individual’s body and given back to him.
- Allogeneic stem cell transplant, where stem cells given to the patient are either donated by an immediate family member or an unrelated person.
- Syngeneic stem cell transplant, whereby stem cells come from the identical twin of the patient.
Besides these three basic types of stem cell transplant, two other types of stem cell transplant exist. However, they are still in the clinical trail stage.
- Tandem autologous transplant, where the patient undergoes two autologous stem cell transplant within a span of six months.
- Mini allogeneic (nonmyeloablative) stem cell transplant, in which the patient undergoes a less intense conditioning process before an allogenic stem cell transplant.
Additionally, adults receiving an allogeneic cord blood stem cell transplant have the unique option of using stem cells from two different donors. While this method is not widely practiced, it has been used successfully in a handful of stem cell transplants.
Can Stem Cells from any Donor be Given to a Patient?
On the surface of our body cells, there are special sets of proteins called human leukocyte associated antigen or HLA-antigen. The more closely the HLA-antigens on the donor’s stem cells match with those on the recipient stem cells, the higher the probability of an allogeneic stem cell transplant being successful. However, if the HLA-antigens are not properly matched, then the recipient’s body may reject the donor’s stem cells. The result of the rejection is the development of graft vs. host disease or GVHD.
There are three different pairs of HLA-antigens that a patient needs to be matched on for a total of six antigens. Patients receiving a bone marrow transplant will need to find a donor that is a perfect match, that is a 6/6 HLA match. On occasion, a transplant may be done even if the recipient is a 5/6 HLA match. Individuals receiving a cord blood transplant, though, can use stem cells from someone that is only a 4/6 HLA match. This is because cord blood stem cells are more immature than bone marrow stem cells and therefore less likely to cause GVHD.
However, GVHD is not an issue with regards to autologous or syngeneic stem cell transplant. In the case of the former, the stem cells used for transplantation are derived from the patient himself, while in the case of the latter the stem cells are derived from the identical twin of the patient who has the same genes and the same HLA-antigens.
How is a Patient Prepared for a Stem Cell Transplant?
Before a stem cell transplant, several tests are performed to assess the overall health and condition of the patient. In addition to these tests, an intravenous catheter may be surgically inserted into a main vein in your chest, up towards your neck. During the duration of the treatment, this catheter will be used for chemotherapy, to infuse the stem cells, for any blood transfusions and even for providing nutrition.
Once the tests have been performed and the intravenous catheter has been inserted, the conditioning session begins. This involves high-dose chemotherapy and total body irradiation (TBI), which are performed in order to destroy the damaged stem cells and suppress the immune system (so as to reduce the chances of stem cell rejection).
The type of conditioning process administered to the patient generally depends upon her overall health, type of disease and the type of stem cell transplant therapy selected for her. Irrespective of the type, the conditioning process is typically associated with numerous side effects, including:
- Nausea and vomiting
- Hair loss
- Mouth ulcers
- Increased risk of organ failure
- Premature menopause
- Development of secondary cancer
What Happens After the Stem Cells Have Been Infused in the Patient?
Upon entering into the blood stream, the stem cells reach the bone marrow and, after a short time, begin producing new blood cells. This process is known as engraftment, which may take about two to four weeks. However, the immune system takes approximately one to two years to recover completely.
Depending upon the treatment procedure, the patient may be required to stay in the hospital for at least three to five weeks or until her blood count becomes normal. Sometimes patients who have undergone stem cell transplant are asked to stay close to the hospital for the next three to four months for close monitoring.
For several weeks following a stem cell transplant, doctors perform different tests to determine whether the newly implanted stem cells are producing new blood cells or not. During this phase, bone marrow aspiration (where a small amount of bone marrow is withdrawn with the aid of a needle and examined under a microscope) may also be performed by doctors to ascertain how well the new bone marrow is functioning.
Although stem cell transplant is associated with many complications in addition to long-term and short-term side effects, it has the potential to cure a large number of congenital as well as acquired diseases. While it is beneficial to evaluate the pros and cons of a stem cell transplant before opting for it, it is important to remember that, after a successful stem cell transplant, the chances of reoccurrence of disease is greatly minimized. The majority of people who have undergone a stem cell transplant are able to lead a completely normal life afterwards.