What are stem cells?

Generally speaking, the term "stem cells" refers to rudimentary cells which give rise to many different types of cells in the body, such as organ, skin, neural, or blood cells. Essentially, a stem cell can become another type of cell and is capable of replicating to produce these differentiated cells as well as more stem cells. They are the means by which cells in the body can be replenished. A unique and important feature of stem cells is their ability to replicate many, many more times than a cell of any one type.

There are two main types of stem cells: adult (also called somatic) stem cells and embryonic stem cells.Embryonic stem cells are inherently more flexible than adult stem cells because they can easily become any other kind of cell, whereas adult stem cells typically form different types of cells within a range, though recent research suggests that with coaxing an adult stem cell can also demonstrate great flexibility, or plasticity.

What does stem cell research hope to accomplish?

Many scientists are hopeful that stem cell research, along with general research about the root causes of diseases, will yield therapies for diseases.

One potential benefit that has been highlighted in the national media is stem cell therapy for spinal cord injuries. Since adult brain and other neural tissues don't reproduce, spinal cord injuries can lead to permanent paralysis. If scientists were able to guide stem cells into becoming nerve cells, these cells could be implanted to help regenerate spinal cord tissue, reversing the damage.

The phenomena might also help treat Parkinson"s disease, multiple sclerosis, diabetes, heart disease, Alzheimer"s disease, and even cancers.

Why is stem cell research controversial?

Much of the controversy surrounding stem cell research deals not with its application, but with its harvesting.

Since embryonic stem cells offer more options for research, the issue is the source of the cells. Currently, embryonic stem cells are most often gleaned from blastocysts (embryos in their fourth or fifth day of development) donated by couples who have undergone invitro fertilization. Scientists penetrate the outer layer of cells to harvest the stem cells inside, which they usually grow on an artificial medium or on genetically modified mouse skin cells that provide nutrients to the stem cells. The blastocyst is usually destroyed in the process. Many groups and religious institutions feel that this is highly unethical because they believe that stem cell research results in the willful destruction of one life for the possible benefit of another.

Such groups also worry that allowing stem cell research might lead to the creation of embryos solely for the purpose of research, which is possible with current technology.

People on the other side of the issue argue that most of the blastocysts used are already slated for disposal by fertility clinics, and thus stem cell research at least provides an avenue for long-term benefit to humanity.

The debate is complicated by the fact that embryonic cells are easier to harvest, and are totipotent; that is, they can give rise to all different types of cells.

Adult stem cells have been harder to find, identify, and coax beyond their typical capacities, though recent experiments to do so have increased the hope for success among scientists.

In the United States, President Bush has proposed a limit on funding for stem cell research. Bush suggests that federal funding only be granted to scientists working with existing embryonic stem cell lines; under his plan, no new embryos will be created or used for research purposes.

Interestingly, though much has been made of this proposal in the media, few realize that this does not prohibit research on new embryonic stem cell lines; it only limits the projects which will receive federal funding. Private research projects can use new lines of embryos if they are independently financed.

Many groups that oppose embryonic stem cell research find the Bush compromise unacceptable and contradictory to his stance on the abortion issue. They point out that the benefits of adult stem cell therapies have been suppressed in the debate, and that recent successes with adult stem cells indicate that embryonic cell research is not necessary.

What are the benefits of using embryonic stem cells?

As mentioned above, the biggest reason scientists tout the use of embryonic stem cells is their ability to transform, easily, into all types of tissues. Historically, scientists have only had success with adult stem cells in producing a few of the body"s 220 types of cells (though that may be changing.) Many argue that in order to produce therapies and treatments for the wide array of currently incurable diseases, a flexible stem cell is absolutely crucial. Embryonic stem cells are also easier to gather, and more importantly, offer a longer research life expectancy than adult stem cells. Eventually, the lines of cells degrade and become scientifically useless, so proponents of embryonic stem cell research stress the need for a continued source of embryo cell lines.

What are the disadvantages of using embryonic stem cells?

An obvious downside of embryonic stem cell research is the ethical issues it raises. Additionally, it is possible that the use of embryonic stem cell therapy in an adult could cause rejection by the adult's immune system, but the research on this has not yet been done.

What are the benefits of using adult stem cells?

One major potential advantage to using adult stem cells is that they can be drawn from the individual in need, grown and transformed in a laboratory, and reintroduced to the body without risk of rejection. Organ and tissue transplants from other sources require the use of immunosuppressant drugs to prevent rejection by the body"s immune system. It also protects the individual from any viruses or other antigens that may be present in another person"s cells.

Another benefit unique to adult stem cell research is the ability to produce cells that release insulin, which impacts diabetes treatment research. In fact, scientists who were hopeful that embryonic stem cells could help cure Type I diabetes found that, in one instance, they actually formed tumors instead.

What are the disadvantages of using adult stem cells?

It is difficult to isolate and extract adult stem cells, and their reproductive capacity is somewhat more limited than that of embryonic stem cells. Additionally, they are much harder to grow and reproduce on a medium outside the body.

An extension of this problem is that obtaining a pure, uniform sample of adult stem cells is highly challenging. This presents a big problem for scientists who rely on constants for experiments, which must be completed and repeated before conclusions may be drawn. It is much more difficult to procure identical adult stem cells, which may severely limit their usefulness to scientists.

Finally, only a few of the 220 types of cells have been produced using adult stem cells. Though evidence of greater plasticity has recently been put forth, the problems mentioned above may prevent the wide application currently available with embryonic stem cells.

The future of stem cell research

The debate about stem cell research is not limited to the United States. Several European countries and China have banned embryonic stem cell research, but other developed nations such as Britain, Israel, and Japan have passed legislation allowing it. Observers on both sides of the argument generally agree that the issue is not likely to fade away, and that future advancements in the areas of stem cell and cloning research will inevitably raise as many questions as answers in years to come.