Umbilical Cord Stem Cells vs. Embryonic Stem Cells
Umbilical Cord Stem Cells vs. Embryonic Stem Cells
Another reader question: “Dear Anne, Some of my associates are clearly opposed to embryonic stem cell research and are promoting umbilical stem cells as an alternative. Could you do a comparison of the two?”
So I poked around and found out that there are two basic disadvantages to umbilical cord stem cells: one is that there are actually very few of them in cord blood, so they are hard to isolate. The other is that they do not grow well in culture compared to embryonic stem cells. While umbilical cord stem cells appear to have the potential to differentiate into nearly as many kinds of cells as hESCs, they are significantly harder to work with.
Another issue with most kinds of stem cell treatments is immune system response. Stem cells from one’s own umbilical cord blood would not produce an immune system response. Great, for people who have banked their blood. But millions of us are too old to have done so. So we would need umbilical cord stem cells from someone else’s blood, which might provoke an immune system response. (The risk is less than with a straight bone marrow donation or organ transplant, but it is still an issue.) With hESC work, the cells that are produced could be a genetic copy of the patient’s own. This scenario assumes that the cells are specially created for the patient as part of a treatment plan. Getting someone else's hESC cells would presumably also create an immune system response. But the point here is that you can create an exact genetic copy with hESCs, which you can't with umbilical cord stem cells.
There are probably situations in which hESC treatment would not be ideal and it would be better to risk an immune system reponse; for example, what is the risk that the cloned stem cells contain the same conditions leading to cancer or a disease as the patient's original cells? hESC treatment might turn out to be appropriate for injury but not cancer, in which case umbilical cord stem cells could be perfect.
Umbilical cord stem cells certainly have great potential. But until their limitations are overcome, hESCs have more therapeutic advantages. Will this be true 10 years from now? Maybe not. The only way we will know is for research in both to continue.
Below are some sources that I consulted for this. I have highlighted the key points myself but otherwise these are copied directly from the web sites. Please go to those web sites for further information or any citation of the information. Thanks.
From the Stem Cell Research Foundation
Adult stem cells are undifferentiated cells that are found in small numbers in most adult tissues. However, they are also found in children and can be extracted from umbilical cord blood. A more accurate phrase is “somatic stem cells,” although this phrase has yet to be generally adopted. The primary roles of adult stem cells in the body are to maintain and repair the tissues in which they are found. They are usually thought of as multipotent cells, giving rise to a closely related family of cells within the tissue. An example is hematopoietic stem cells, which form all the various cells in the blood. Recent evidence, however, indicates that some adult stem cell types may be pluripotent, or at least able to differentiate into multiple cell types. For example, hematopoietic stem cells can differentiate into neurons, glia, skeletal muscle cells, heart muscle cells, and liver cells. Whether they actually do this ordinarily within the body is unknown. Blood from the placenta and umbilical cord that are left over after birth is a rich source of hematopoietic stem cells. These so-called umbilical cord stem cells have been shown to be able to differentiate into bone cells and neurons, as well as the cells lining the inside of blood vessels. A potential advantage of using adult stem cells from a patient is that the patient’s own cells could be expanded in culture, treated to differentiate into the desired cells, and then reintroduced into the patient. The use of the patient’s own cells would eliminate any possibility that they might be rejected by the immune system. Disadvantages of using adult stem cells are that they are rare in mature tissues and it is more difficult to expand their numbers in cell culture, compared with ESCs.
From the National Institute of Health
Why not use adult stem cells instead of using human embryonic stem cells in research?
Human embryonic stem cells are thought to have much greater developmental potential than adult stem cells. This means that embryonic stem cells may be pluripotent—that is, able to give rise to cells found in all tissues of the embryo except for germ cells rather than being merely multipotent—restricted to specific subpopulations of cell types, as adult stem cells are thought to be.
From the International Society for Stem Cell Research
Umbilical cord blood stem cells can be obtained from the umbilical cord immediately after birth. Like bone marrow, umbilical cord blood is another rich source of hematopoietic stem cells. These hematopoietic stem cells are usually referred to as neonatal stem cells and are less mature than those stem cells found in the bone marrow of adults or children.
The advantages of using cord blood as a source of stem cells are its non-invasive procurement and its vast abundance; thousands of babies are born each day. Until recently, umbilical cord blood was discarded after birth, along with the placenta. Now, in several countries around the world, cord blood is collected and either banked in public banks for general use, or stored by private companies for private use, in private cord blood banks.
Cord blood has recently emerged as an alternative source of hematopoietic stem cells for treatment of leukemia and other blood disorders. In these applications, umbilical cord blood has the notable advantage that despite its high content of immune cells, it does not produce strong graft-versus-host disease, a condition where the graft immune cells attack the patient's body cells. Therefore, cord blood grafts do not need to be as rigorously matched to a recipient as bone marrow grafts.
This expands the available donor pool for hematopoietic stem cell transplants considerably. However, a disadvantage of umbilical cord blood, and an argument against generalized use, is the limited number of stem cells in any given cord. This increases the risk of graft failure once transplanted into an adult.
The use of umbilical cord blood stem cells for other uses, such as organ and tissue repair, is under investigation. However, the stem cells themselves would be recognized as foreign and rejected the same way as a transplanted organ, unless the patient's immune system is strongly suppressed, or has been ablated before transplantation, such as is the case prior to bone marrow transplantations.
Also from the ISSCR:
8. What is unique about stem cells from baby teeth or umbilical cords? Stem cells from umbilical cord blood or the pulp under baby teeth are "younger" stem cells than those obtained from adults. They are able to divide for longer times in cell cultures than most adult stem cells, and may give rise to different tissues. Their potential to form many different cell types is currently being explored.
Umbilical cord blood stem cells are used for stem cell transplantation to reconstitute blood cell formation (the hematopoietic system) in patients that have been irradiated or treated with specific drugs for cancer or leukemia. Also, in some genetic diseases, where patients have a problem forming normal blood cells, a transplantation of matched umbilical cord blood cells can give them a new blood-forming system.
The new cells are infused into the vein of the patient and then they are able to find their way into the bone marrow, in a process called "stem cell homing."
And here is an article discussing the issue:
The Science Correspondent for the on-line magazine Reason wrote about umbilical cord stem cells a year ago. He wrote, “For example, one current problem with stem cells from umbilical cord blood is that they do not continually renew in culture without differentiating like human embryonic stem cells do.” His conclusion was one that I have also come to as I have read about stem cell cells, and in fact is very similar to the point I made above and in a previous post (Americans Support Stem Cell Research, 10/24/05):
However, only more research will tell whether the promise of adult umbilical cord and embryonic stem cells will be fulfilled. Various lines of research should be pursued simultaneously to insure the best chance of discovering effective future treatments. It may well turn out that adult stem cells are good treatments for certain diseases, umbilical ord stem cells work best for others, and embryonic stem cells are better at curing still different maladies. Contrary to the claims of ioconservatives, it is not either adult and umbilical cord stem cells or embryonic ones; for the sake of millions of suffering patients, it's necessary to forge ahead on all three fronts.Here is the link to his full article: