Stem Cell Transplantation

Definition

Stem cells are basic human cells that reproduce (replicate) easily, providing a continuous source of new, sometimes different types of cells. A stem cell transplant is a procedure that replaces unhealthy stem cells with healthy ones.

Purpose

Physicians use stem cell transplants to treat many diseases that damage or destroy bone marrow, found in the soft fatty tissue inside the bones. Examples of these diseases are leukemia and multiple myeloma. Some patients lack bone marrow because of aggressive cancer treatments or diseases such as aplastic anemia, which causes abnormal blood cell production.

Recent advances in stem cell research have made it a treatment possibility for patients with certain types of lymphomas, genetic disorders, and autoimmune disorders as well. Researchers are hoping to eventually harvest stem cells to treat diseases such as Parkinson's disease, type 1 diabetes, Alzheimer's disease, liver disease, arthritis, and spinal cord injuries.

Precautions

The physician will weigh many factors when determining if a patient is a candidate for stem cell transplantation, including overall health and function of many vital organ systems. Stem cell transplantation is an aggressive treatment and may not be recommended for some patients, including those with heart, kidney, or lung disorders. If the patient has an aggressive cancer that has spread throughout the body, he or she may not be considered for a stem cell transplant. It once was thought that stem cell transplants were not safe in patients over age 60, but new research shows that elderly patients can safely receive stem cells from donors.

Many ethical and legal factors are impacting the research and development into stem cell transplantation. Much debate surrounds scientific advances. For example, human embryos, fetal tissues and umbilical cords are sources of stem cells that may be transplanted or used for disease research. Some people have ethical problems with the use of embryos in fertility clinics for stem cell research or transplantation. Some link stem cell transplantation for disease with cloning and want to stop funding for stem cell research over fear of human cloning. A study released in 2005 stated that 63% of Americans back embryonic stem cell research and 70% support federal legislation to promote more research. Meanwhile, scientists continue to develop new and exciting possibilities for transplanting stem cells into the human body that may one day lead to new treatments for previously incurable diseases. Many do so with private funding.

Description

Stem cell transplants sometimes are called bone marrow transplants. Nearly 100 years ago, physicians tried to give patients with leukemia and anemia bone marrow by mouth. These treatments were not successful, but led to experiments showing healthy bone marrow transfused into the blood stream could restore damaged bone marrow.

Today, two types of stem cell transplants are performed most often. When a patient's own stem cells are collected (harvested) before they are destroyed by high-dose chemotherapy or radiation therapy treatments, then returned to the same patient's body, it is called an autologous transplant. Using stem cells from another person, or a donor, is called allogenic transplant. In many cases, donor cells come from a relative, such as a brother or sister. However, the likelihood that a sibling will match the patient is only about 25%. Stem cells may need to come from a person not related to the recipient.

To find out if a patient could receive stem cells from a donor, physicians developed human leukocyte antigen (HLA) testing to match tissue types. The next challenge became finding donors. Throughout the 1980s and 1990s, private individuals, hospitals, foundations, and states worked to set up a nationwide registry of bone marrow donors. The National Marrow Donor Program (NMDP) now has the largest stem cell donor registry in the world. In July 2003, more than five million volunteer donors and more than 28,000 units of umbilical cord blood were listed on the NMDP registry. More than 16,000 bone marrow transplants have been performed since the NMDP was founded in 1986.

Stem cell transplants normally take place at specialized centers. Donor cells are taken from the donor in an operating room while the patient is unconscious and under general anesthesia. Bone marrow normally is harvested from the top of the hip bone. The marrow usually is filtered, treated, and either transplanted immediately or frozen for later use. Stem cells are transfused through an intravenous (IV) catheter that physicians insert in the patient's neck or chest. Physicians refer to this step as the "rescue process." The stem cells replace old cells. For example, the transplanted cells travel to the bone cavities and begin replacing old bone marrow.

Preparation

Standard preparation involves getting rid of the remaining disease and damaged cells. The exact process depends on the patient. In many cases, the patient will receive chemotherapy. Some also receive radiation therapy. Another goal of preparation is to depress the immune system. This makes it less likely that the patient's body will reject the new stem cells. New advances have been made that allow some of the patient's diseased cells to remain and mix with the new cells. Immediately before transplantation, the treating physician and staff will give the patient special instructions and precautions, depending on his or her disease and exact procedure.

Aftercare

Stem cells take up to three weeks to begin producing new cells or bone marrow, a process called engraftment. Until engraftment is complete, patients may bleed easily and are at risk for infections. They may be required to stay in the hospital at least one week following surgery until blood cell counts reach a safe level. Once home, patients usually must be closely monitored, be careful not to risk infection, and may be anemic and sleep most of the time. They may receive antibiotics to prevent infection and will receive specific instructions for care from the transplant center staff. Most stem cell transplant patients cannot return to work or normal activities for up to six months following the transplant.

Risks

In addition to the risk of a life-threatening infection following a stem cell transplant, patients receiving stem cells from donors risk serious complications from graft-versus-host disease (GVHD). GVHD is caused when the donor's cells react against the patient's (recipient s) tissue. Sometimes, the patient's body simply rejects the new cells. Researchers continue to explore ways to lessen risks of complications following stem cell transplants. For example, recent studies recommend a measles vaccination after stem cell transplantation to prevent measles in recipients, who are at risk because of their low immunity.

KEY TERMS

Catheter— A medical device shaped like a tube that physicians can insert into vessels, canals, or passageways to more easily inject or withdraw fluids.

Embryo— A developing human from the time of conception to the end of the eighth week after conception.

Engraftment— The process of transplanted stem cells reproducing new cells.

Normal results

When bone marrow transplantation is successful, it prolongs the life of a person who might have otherwise died from the disease that caused damage to the bone marrow. People with more siblings have a higher chance of finding a compatible donor, though successful stem cell transplants also occur with donors who are not related to the recipients. Patients usually can return to normal activities within six months to one year after the transplant.

Resources

PERIODICALS

"Allogenic Stem Cell Transplantation Is Safe in Elderly Patients." Immunotherapy Weekly (Sept. 22, 2004):195.

"More Americans Backing Stem Cell Research, Says Study." Pharma Marketletter (Feb. 21, 2005).

"Patients Should Receive Measles Vaccine After Stem Cell Transplantation." Life Science Weekly (Nov. 23, 2004):883.

ORGANIZATIONS

International Myeloma Foundation. 12650 Riverside Drive, Suite 206. North Hollywood, CA 91607-3421. 800-452-CURE. http://www.myeloma.org.

National Marrow Donor Program. Suite 500, 3001 Broadway St. NE, Minneapolis, MN 55413-1753. 800-627-7692. http://www.marrow.org.

OTHER

Advances in Stem Cell Transplants: A Primer for Patients. Web page. National Marrow Donor Program, 2005. http://www.marrow.org/PATIENT/advances_stem_cell_transplants_primer_patients.html.