4. What are the obstacles that must be overcome before the potential uses of stem cells will be realized?
One of the first obstacles that must be overcome is the difficulty in identifying stem cells from adult tissues, which contain numerous mixtures of various cells. The process of identifying and growing the right kind of stem cell, usually a very rare cell in the adult tissue, involves painstaking research. Second, once stem cells are identified and isolated, the right conditions must be developed to cause these cells to differentiate into the specialized cells. This too will require a great deal of experimentation.

In general, embryonic and fetal stem cells are believed to be more versatile than adult stem cells. However, scientists are still working on developing proper conditions to differentiate embryonic stem cells into specialized cells. As embryonic stem cells grow very fast, scientists must be very careful in fully differentiating them into specialized cells. Otherwise, any remaining embryonic stem cells can grow uncontrolled and form tumors.

Assuming that the above obstacles can be overcome, new issues arise when the specialized cells (grown from stem cells) are implanted into a person. The cells must be integrated into the patient's own tissues and organs and "learn" to function in concert with the body's natural cells. Cardiac cells that beat in a cell culture, for example, may not beat in rhythm with a patient's own heart cells. And neurons injected into a damaged brain must become "wired into" the brain's intricate network of cells and their connections in order to work properly.
 
Yet another challenge is the phenomenon of tissue rejection. Just as in organ transplants, the body's immune cells will recognize transplanted cells as "foreign," setting off an immune reaction that could cause the transplant to fail and possibly endanger the patient. Cell recipients would have to take drugs to temporarily suppress their immune systems, which in itself could be dangerous.

Thus, research on stem cells and their applications to treat various diseases is still at a preliminary stage. However, results from animal models are very promising and many researchers believe that it is only a matter of time before the same results can be achieved with human stem cells.

5. What is a stem cell line?
A stem cell line is composed of a population of cells that can replicate themselves for long periods of time in vitro, meaning out of the body. These cell lines are grown in incubators with specialized growth factor-containing media, at a temperature and oxygen/carbon dioxide mixture resembling that found in the mammalian body.

Embryonic stem cell lines, both human and mouse, can be grown indefinitely in vitro if the correct conditions are met. Importantly, these cells continue to retain their ability to form different, specialized cell types once they are removed from the special conditions that keep them in an undifferentiated, or unspecialized, state.

A limited number of human embryonic stem cell lines have been approved for use by scientists receiving federal funds in the United States. In August 2001, President Bush mandated that if scientists were using federal funds, research could only be conducted on the cell lines that were already in existence, grown from fertilized eggs that were to be discarded at in vitro fertilization clinics.

This regulation stated that no additional human stem cell lines could be generated from additional blastocysts. In the long term, this will place severe restrictions on the scientific process in this field and will limit the ability of scientists to compare the potential of human embryonic stem cell lines for tissue repair, to that which can be accomplished from other sources, such as adult stem cells.

6. What is an embryonic stem cell?
Embryonic stem cells are derived from the cells that make up the inner cell mass of the blastocyst. Both mouse and human embryonic stem cell lines exist. Mouse embryonic stem cells are capable of generating any and all cells in the body, under the right conditions. Therefore, they are said to be pluripotent and have unlimited potential as far as growth and differentiation. The cells divide continuously in tissue culture dishes in an incubator, but at the same time maintain the ability to generate any cell type when placed into the correct Environment to cause their differentiation.

Human embryonic stem cell lines are currently being studied and several research teams are working to determine whether or not they possess the same properties as mouse embryonic stem cells. Because human embryonic stem cells were isolated relatively recently, and therefore we know less about them, it is currently more difficult to work with human systems than mouse. However, scientists are making remarkable progress that could ultimately lead to therapies to replace or restore damaged tissues using these human cells.

7. What is an adult stem cell?
Adult stem cells are distinct from cells isolated from embryos or fetuses and are found in tissues that have already developed, as in animals or humans after birth. These cells can be isolated from many tissues, including brain. However, the most common place to obtain these cells is from the bone marrow that is located in the center of some bones. The marrow is harvested from human donors at the iliac crest (the back of the upper hip bone).

There are different types of stem cells found in the bone marrow, including hematopoietic stem cells, endothelial stem cells, and mesenchymal stem cells. It has long been known that hematopoietic stem cells form blood, endothelial stem cells form the vascular system (arteries and veins), and mesenchymal stem cells form bone, cartilage, muscle, fat, and fibroblasts.

Recently a theory of "stem cell Plasticity" has been put forth, which suggests that some adult stem cells may have a broader potential to form different cell types than was previously suspected. That means cells from the bone marrow, originally thought to be purely blood-forming cells, may contribute to Regeneration of damaged livers, kidneys, hearts, lungs and other organs.

Although this field is extremely exciting, it is highly controversial in the scientific community and needs additional carefully documented research to understand the full potential of the adult stem cells, and in particular how they compare to embryonic stem cells.

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."