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| Cord Blood |
What is a Cord Blood?
Cord blood is easily defined as blood retrieved from the umbilical cord after the birth of the child. The cord blood contains stem cells which are considered the building blocks of blood and immune systems in the body. Stem cells can also be found in the bone marrow and blood that circulates within the body. However, cord blood is the most desirable because they are the youngest and have not endured much aging or damage. If a person's blood stem cells become damaged due to diseases, cancer, or leukemia, the only hope for a cure is a blood stem cell transplant. This replaces the patient's diseased cells with healthy new stem cells. The cells that will be transplanted in must match the patient's cells to reduce the risk of Graft-Versus-Host Disease (GVHD).
In the 1970s medical researchers discovered that human umbilical cord blood contained the same kind of stem cells found in bone marrow. (Stem cells get their name from their ability to develop into three types of blood cells: red blood cells, while blood cells and platelets). Because stem cells from bone marrow had already been used successfully to treat patients with life-threatening blood diseases, such as leukemia and immune system disorders, researchers believed that they could also use stem cells from cord blood to save patients.
In 1988, doctors transplanted human umbilical cord blood into a 5-year old boy suffering from Fanconi's anemia. Ten years after the transplant, the boy is alive and seems to be cured of his disease. Based on this and other successful transplants, doctors and medical researchers began to collect, freeze and store cord blood units (CBUs) at cord banks throughout the world. As of October 1998, there were approximately 22,000 CBUs collected and frozen for use worldwide, and approximately 700 unrelated donor and 150 related (sibling) donor cord blood transplants had been performed.
Although today marrow transplants and cord blood transplants are often referred to by the same name -- stem cell transplants -- there are important differences between the two. This article will explain these differences and also discuss the kinds of decisions doctors and their patients must make to determine the best source of stem cells for transplantation. Before considering these issues, however, it is important to understand the challenges patients face in finding a donor.
Finding a Donor
Unfortunately, 70% of patients who need a stem cell transplant do not have a suitable donor in their family. The National Marrow Donor Program (NMDP) helps identify stem cell donors for patients who do not have a related donor.
Stem cell transplants require matching certain tissue traits of the donor and patient. Because these traits are inherited, a patient's most likely match is someone of the same heritage. American Indian and Alaska Native, Asian, Black and African American, Hispanic and Latino, Native Hawaiian and Other Pacific Islander, and multiple-race patients face a greater challenge in finding a match than White patients.
The collection and storage of cord blood is one way to give patients of all racial and ethnic backgrounds greater access to stem cell transplantation. For that reason, beginning in the early to mid-1990s, medical institutions around the world began making a serious effort to collect and store cord blood units for use in transplantation.
Clinical Results
So far, clinical studies by John E. Wagner and others suggest that unrelated cord blood transplantation is a safe and acceptable alternative to bone marrow transplantation for many patients. However, these studies have also found that, as with bone marrow transplants, patients who receive cord blood from sibling (or related) donors generally have higher survival rates than those who receive cord blood from unrelated donors.
Studies have also found that banked cord blood (from both related and unrelated donors) often contains enough stem cells for transplantation. Physicians need to match the number of stem cells in a cord blood unit with the weight of the patient to be sure the unit is likely to be able to reestablish the patient's immune system. Because there are fewer stem cells in cord blood than in marrow, until recently most cord blood recipients have been children or small adults. There is, therefore, some concern that the number of cells in an average cord blood unit may not be sufficient for engraftment in larger adults. Engraftment occurs when the transplanted stem cells -- the "graft" -- regenerate the blood and marrow and begin to function as the recipient's new immune system.
One positive finding is that cord blood transplant patients appear to suffer less from acute graft-versus-host disease (GVHD) than patients who receive bone marrow transplants. GVHD is a very serious, and sometimes fatal, condition that occurs when the patient's new immune system -- which is made up of stem cells from the donor -- starts attacking the patient's body. GVHD affects the skin and internal organs such as the liver and intestines.
Despite the fact that cord blood recipients appear to suffer less from GVHD, it has not yet been proven that the risk of GVHD is less in all recipients after cord blood transplantation. Because children receive the most cord blood transplants, and because they also experience less GVHD than adults after bone marrow transplants, it may be that the success of cord blood transplants is at least partly attributable to the fact that they are used on more children than adults.
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