Stem Cell FAQ

What are stem cells, and what might they mean for medicine and the rest of the world?
Stem cells are tiny, but they draw big-time attention from scientists, patients, lawmakers, celebrities, and people of every other background.

Stem cell headlines are a hive of buzzwords — “embryonic” this and “adult” that — as well as controversy.

But you needn’t be a PhD to understand the basics of stem cells.

If you think of your body as a car, so far doctors have had the ability only to repair a defective part or, at best, take a part out of another car and put it into you (organ transplantation). Stem cells can theoretically grow and develop into any spare part you need, so it is as if the doctor can just call the car manufacturer and get the original replacement part. As you can imagine, this could have the potential to cure a tremendous number of diseases.

The main reason there is a big debate over the use of stem cells is that these cells can come from an embryo. To many people, an embryo is a living human being and destroying an embryo for any reason is morally unacceptable. People on the other side of the debate say that embryonic stem cells have the potential to cure many diseases and the embryos used would have been discarded by fertility clinics anyway.

Leaving the ethical debate behind, here is what we know – and what we don’t know — about stem cells. Just the medical facts, ma’am.

Q: What are stem cells?

A: All of us start from a single cell formed at conception, when a sperm cell joins with an egg. This cell then starts dividing and forms a ball of cells. About four days after conception, this ball of stem cells starts changing its shape, and individual cells in that ball start changing and becoming different from their neighbors. At this time, the ball of cells is smaller than a pinpoint. This process, called differentiation, allows some cells to become liver cells and other cells to become nerve cells or skin cells and so on.

This process is similar to the way in which a plant grows. In the beginning, a stem grows out of the seed you planted, which then has branches, and eventually leaves, fruits, and flowers grow on those branches.

These earliest “stem” cells in the embryo give rise to all the different cells in the body.

Adult Stem Cells vs. Embryonic Stem Cells

Q: What’s the difference between adult stem cells and stem cells taken from an embryo?

A: Embryonic stem cells are stem cells that you take from an embryo, and adult stem cells are stem cells you take from a person (adult or child) or from the umbilical cord.

Scientists have found that a few stem cells persist even after we are born. It seems that these adult cells are a kind of backup, so if a particular kind of cell needs replacing, the adult stem cells can differentiate and form those cells. Most adult stem cells can form a limited number of cell types.

Q: Why not just do research on adult stem cells?

A: Adult stem cells definitely have some advantages over embryonic stem cells. First, most people have no ethical problem with using them.

Second, these are cells from your own body, so your immune system will probably not try to reject them. If you use cells that are not part of your body, your body’s immune system may see them as intruders and try to kill them.

But scientists have found three main disadvantages to using adult stem cells.

  • First, these are more mature stem cells. They can form several types of cells — for example, experiments with animals showed that stem cells from the blood can form skin cells, liver cells, and others — but they do not have the ability to form all types of cells. So these cells may be able to cure a limited number of diseases. In comparison, stem cells from embryos can generate any kind of cell and have the potential to cure many more diseases.
  • Second, adult stem cells are hard to identify. There are billions of cells in the body, and to identify these stem cells is worse than looking for the proverbial needle in a haystack. Even when they are found, they are present in very small amounts. Embryonic stem cells are very easy to identify because all cells in a young embryo can be coaxed into developing into any type of cell. These cells can also be made to divide indefinitely, so you can generate a virtually limitless supply of these cells.
  • Finally, adult stem cells take a long time to grow. So far, experiments on adult stem cells from animals have shown that even if you find them, it can take months for them to grow into the particular type of cell that you need. These cells may not be able to grow fast enough to help someone who is very sick. Embryonic stem cells, on the other hand, could be made to grow into several different cell types and stored, so that when a sick person came in the doctor could just thaw the cells and use them.

Finding Embryonic Stem Cells

Q: Where do scientists get the embryos they use?

A: Couples who have difficulty having a baby often use a technique called in vitro fertilization (IVF). Doctors collect eggs from the mother and sperm from the father, and put them together in the laboratory. When the eggs have been fertilized, the doctors implant one or more of the embryos in the mother. The rest are frozen and stored, in case the first embryo implanted doesn’t grow into a baby.

If the mother becomes pregnant and has a baby, she may not want to use the remaining frozen embryos. Then she and her husband can give doctors permission to throw them away, or give them to scientists to use for stem cell research.

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