Stem Cells, Part 2 – How are they obtained?

Adult Stem Cells

The term “adult stem cells” is somewhat misleading. Adult stem cells do not come exclusively from adults. Human adult stem cells are obtained from a developed person, whether he is a senior citizen, an adult, an adolescent, a child, or even a fetus. Perhaps they should be called “somatic stem cells” because they can be obtained from body tissue. Adult stem cells are cells that have not yet developed into specialized tissue, but are capable of doing so, and are also capable of reproducing themselves indefinitely.

Adult stem cells can be obtained from many places in the body. The most familiar source, because it was the first to be used to treat illness in real persons is from the bone marrow.
Adult stem cells are unspecialized cells that are present in small quantities in already specialized tissue. They are needed by the body because both illness and age destroy tissue cells, and the stem cells can regenerate that damage. Adult stem cells also allow for growth.

Adult stem cells can be used for therapy to treat conditions that involve cell degeneration or even abnormalities. Once again, the flagship example is bone marrow stem cells. A treatment for leukemia, a cancer of the blood, involves taking bone marrow from the patient or a blood relative, extracting the stem cells, treating the extracted material by growing it in a nutritive solution, using drugs or radiation to destroy the patient’s abnormal bone marrow, then reintroducing the extracted material into the patient, where it develops into normally functioning bone marrow. This has been done regularly for more than three decades, and is a well established medical practice.

Researchers have reported finding adult stem cells in bone marrow, muscle tissue, liver tissue, fat, nasal mucus tissue, blood and blood vessels, brain tissue, and skin. Adult stem cells are also richly present in umbilical cord and placenta (“afterbirth”). A thorough summary of the state of research on adult stem cells as of 2003 is located here.

Embryonic Stem Cells

As you will recall from part 1 of this series, what are called embryonic stem cells are really the type of stem cells that are termed “pluripotent”; they are capable of developing into any of the more than 200 types of cells in the human body. This stage of development only exists in nature between conception and a few days later, when the fertilized egg has started to divide, but before the specialization process starts.

There are currently only two ways to obtain embryonic stem cells; the first and most common way is to extract them from a pre-embryo (“blastocyst”), and the other by a process called nuclear transfer, commonly referred to as “therapeutic cloning”.

The only practical source of blastocysts that can be used by scientists is the ones created by them in the laboratory. This process is frequently called “artificial conception” or “in-vitro fertilization”, and is aimed primarily towards assisting women who for one reason or another are unable to conceive in the normal way.

The process involves extracting a large number of eggs from the ovary of a volunteer, combining these ova with the sperm of a volunteer in laboratory conditions, testing the results to determine whether a successful fertilization has occurred, and if so, implanting the fertilized ovum in the uterus of a volunteer. Ideally, the sperm and egg donors are the father and mother, but not always. A woman undergoing this procedure may be unable to ovulate and will need another woman’s ova, or she may ovulate normally but be unable to carry the child, and a surrogate mother will provide the uterus.

This is a very “hit-or-miss” process with a low yield of successfully fertilized eggs. Consequently, because of the difficulty and expense involved, a large number of eggs are extracted and processed in this manner. This leads to a situation where sometimes extra fertilized eggs become available briefly. That is the source of the existing embryonic stem cells that are currently available to the researcher.

The other process, called nuclear transfer, starts with a human ovum also. In the laboratory, the researcher cuts into the ovum, removes the nucleus (the part that carries all the genetic material) and replaces it with the nucleus of an adult cell. If this hybrid cell is nurtured properly, it will develop into a new blastocyst that contains only the genetic information of the person who donated the adult tissue cell from which the nucleus was obtained. Such an individual then will be a clone, with DNA that is identical to the nucleus donor.

In common terminology, this is sometimes called “therapeutic cloning”, but this is also a misnomer. Nothing in the way of therapy can be done with this clone currently (although the research for which it was created may some day do so), so it more precisely should be called “cloning for research”.

A good description of how embryonic stem cells are made can be found here. And this article describes what is involved in Somatic Cell Nuclear Transfer (SCNT).

Next: Stem Cells, Part 3 - How are they handled in research?