Stem cell transplantation is the removal of stem cells (undifferentiated cells) from a healthy person and their injection into someone who has a serious blood disorder.
(See also Overview of Transplantation.)
Stem cells are unspecialized cells from which other more specialized cells can be derived. Stem cells may be obtained from
Blood removed from a vein
Bone marrow (bone marrow transplantation)
Blood in the umbilical cord of a baby after it is born (donated by the mother)
Blood is preferred to bone marrow as a source because the procedure is less invasive and the number (count) of blood cells returns to normal more quickly. Stem cells from umbilical cords are usually used only in children because umbilical cord blood does not contain enough stem cells to use in adults.
What Are Stem Cells?
Stem cells are undifferentiated cells that have the potential to become one of 200 types of cells in the body, including blood, nerve, muscle, heart, glandular, and skin cells. Some stem cells can be triggered to become any kind of cell in the body. Others are already partially differentiated and can only become, for example, some kinds of nerve cell. Stem cells divide, producing more stem cells, until they are triggered to specialize. Then as they continue to divide, they become more and more specialized until they lose the ability to be anything but one kind of cell. Researchers hope to use stem cells to repair or replace cells or tissues damaged or destroyed by such disorders as Parkinson disease, diabetes, and spinal injuries. By triggering certain genes, researchers may be able to cause the stem cells to specialize and become the cells that need to be replaced. Researchers are so far able to obtain stem cells from the following sources:
Embryos: During in vitro fertilization, sperm from the man and several eggs from the woman are placed in a culture dish. The sperm fertilizes the egg and the resulting cell divides, forming an embryo. Several of the healthiest-looking embryos are placed in the woman’s uterus. The rest are discarded or frozen to be used later if needed. Stem cells can be obtained from the embryos that are not used. Because the embryos then lose the ability to grow into a complete human being, the use of stem cells from embryos is controversial. But researchers think that these stem cells have the most potential for producing different kinds of cells and for surviving after transplantation. Fetuses: After 8 weeks of development, an embryo is called a fetus. Stem cells can be obtained from fetuses that have been miscarried or aborted. Umbilical cord: Stem cells can be obtained from the blood in the umbilical cord or placenta after a baby is born. These stem cells can produce different types of blood cells. Children and adults: The bone marrow and blood of children and adults contain stem cells. These stem cells can produce only blood cells. These stem cells are most often used for transplantation. Induced pluripotent stem cells: Scientists are developing ways of enabling (inducing) other cells (such as a blood or skin cell) to act as stem cells. These cells are taken from adults. One way to induce these cells is to inject them with material that affects their genes, a process called reprogramming. Development and use of induced stem cells is still considered experimental. |
Although stem cells in theory can become any other type of cell, in practice, stem cell transplantation is used mainly as part of the treatment for blood disorders such as leukemia, certain types of lymphoma (including Hodgkin lymphoma), aplastic anemia, thalassemia, sickle cell disease. Sometimes stem cell transplantation is used for congenital metabolic or immunodeficiency disorders (such as chronic granulomatous disease).
Stem cell transplants may also be given to people who have been treated with high doses of chemotherapy or radiation therapy for certain cancers. Such treatments destroy bone marrow, which produces stem cells. Occasionally, stem cell transplants can be used to replace bone marrow cells that are destroyed during treatment of cancers in organs, such as breast cancer or neuroblastoma (a common childhood cancer that develops from nerve tissue). Doctors are studying how to use stem cell transplantation to treat some autoimmune disorders, such as multiple sclerosis.
About 30 to 40% of people who had lymphoma and 20 to 50% of those who had leukemia are cancer-free after treatments, including stem cell transplantation. The procedure prolongs life in people with multiple myeloma. It is less effective for breast cancer.
Procedure for Stem Cell Transplantation
Stem cells may be
The person’s own cells (autologous transplantation)
Those of a donor (allogeneic transplantation)
If people with cancer are being given their own stem cells, the cells are collected before chemotherapy or radiation therapy, which can damage stem cells. The cells are injected back into the body after the treatment.
If the stem cells come from a donor, the recipient is given drugs to suppress the immune system (immunosuppressants) before stem cells are transplanted.
If the stem cells are intended to replace the blood-forming cells in the recipient's bone marrow, the recipient is given a combination of drugs and radiation treatments to eliminate bone marrow cells that would keep the transplanted cells from surviving.
Stem cells from blood
Stem cells from adults can be obtained from blood during an outpatient procedure. First, a few days before stem cells are obtained, the donor is given drugs that cause the bone marrow to release more stem cells into the bloodstream (called colony-stimulating factors). Then blood is removed through a catheter inserted in one arm and is circulated through a machine that removes stem cells. The rest of the blood is returned to the person through a catheter inserted in the other arm. Usually, about six 2- to 4-hour sessions over a period of several days are needed, until enough stem cells are obtained. Stem cells can be preserved for later use by freezing them. Stem cells can also be obtained from the umbilical cord of a baby after delivery and frozen for future use.
Stem cells from bone marrow
For bone marrow transplantation, the donor is given a general or local anesthetic. Doctors then remove marrow from the donor’s hip bone with a syringe. Removal of bone marrow takes about 1 hour.
To recipient
Stem cells are injected into the recipient’s vein over a period of 1 to 2 hours. The injected stem cells migrate to and begin to multiply in the recipient’s bones and produce blood cells.
After the stem cell transplantation
After transplantation, drugs are given to prevent complications (see below).
Recipients of a stem cell transplant usually remain in the hospital for 1 to 2 months.
After discharge from the hospital, follow-up visits are scheduled at regular intervals. Most people need at least 1 year to recover.
Complications of Stem Cell Transplantation
Infections
Stem cell transplantation is risky because the recipient’s white blood cells have been destroyed or reduced in number by chemotherapy or radiation therapy. As a result, the risk of infection is very high for about 2 to 3 weeks—until the donated stem cells can produce enough white blood cells to protect against infections.
The risk of infection can be reduced by keeping the recipient in isolation for a period of time (until the transplanted cells begin to produce white blood cells). During this time, everyone entering the room must wear masks and gowns and wash their hands thoroughly.
The recipient is given
Colony-stimulating factors, which stimulate the production of blood cells (including white blood cells, which help fight infection)
Antimicrobial drugs to help reduce the risk of infection
Graft-versus-host disease
The new bone marrow obtained from another person may produce cells that attack the recipient’s cells, causing graft-versus-host disease. This disease causes death in about 20 to 40% of people who develop it.
So if the bone marrow came from another person, recipients are given immunosuppressants to prevent graft-versus-host disease and rejection.
Recurrence of the original disorder
Whether the original disorder returns depends on
What the original disorder was
How severe it was
What type of transplant was used
The original disorder returns in
40 to 75% of people who are given their own stem cells
10 to 40% of people who are given stem cells from other people
