STEM CELL THERAPY > INFORMATION > SHEET 6

What Are the Alternatives?

"We see the possible cloning of human embryos in this way as an aid to research rather than as a routine way of creating stem cells for every patient. Very few human eggs are available as surplus to requirements from IVF clinics in the UK whereas the numbers of potential patients for cell therapy runs into hundreds of thousands. On practical grounds alone it will, therefore, be essential to find ways of avoiding the use of human eggs if stem cell therapy is to achieve its true potential."
Dr Harry Griffin, Assistant Director, Roslin Institute

In June this year scientists at the Karolinska Institute in Stockholm discovered that it was technically possible for the stem cells found in the adult brain to develop into almost any of the specialised cells of the body.

The study showed that when the brain cells of adult mice are placed alongside embryonic cells, they can be reprogrammed to develop into quite different cell-types.

However, as yet, the scientists involved do not know why this happens. One theory is that the embryo could be sending out chemical signals that take control of the adult stem cells although the scientists have not been able to isolate these signals.

But many scientists maintain that working with embryos offers far greater potential advantages than adult stem cells.

The following article explains the position in May 2000 with regard to the use of adult stem cells. This research is constantly changing so for an update try the following websites:

National Institutes of Health: http://www.nih.gov/news
Roslin Institute: http://www.ri.bbsrc.ac.uk
New Scientist: http://www.newscientist.com

Do adult stem cells have the same potential as pluripotent stem cells?

Until recently, there was little evidence in mammals that multipotent cells such as blood stem cells could change course and produce skin cells, liver cells or any cell other than a blood stem cell or a specific type of blood cell; however, research in animals is leading scientists to question this view.

In animals it has been shown that some adult stem cells previously thought to be committed to the development of one line of specialised cells are able to develop into other types of specialised cells. For example, recent experiments in mice suggest that when neural stem cells were placed into the bone marrow, they appeared to produce a variety of blood cell types.

In addition, studies with rats have indicated that stem cells found in the bone marrow were able to produce liver cells. These exciting findings suggest that even after a stem cell has begun to specialise, the stem cell may, under certain conditions, be more flexible than first thought.

Why not just pursue research with adult stem cells?

Research on human adult stem cells suggests that these multipotent cells have great potential for use in both research and in the development of cell therapies.

For example, there would be many advantages to using adult stem cells for transplantation. If we could isolate the adult stem cells from a patient, coax them to divide and direct their specialisation and then transplant them back into the patient, it is unlikely that such cells would be rejected.

The use of adult stem cells for such cell therapies would certainly reduce or even avoid the practice of using stem cells that were derived from human embryos or human fetal tissue, sources that trouble many people on ethical grounds.

While adult stem cells hold real promise, there are some significant limitations to what we may or may not be able to accomplish with them. First of all, stem cells from adults have not been isolated for all tissues of the body.

Although many different kinds of multipotent stem cells have been identified, adult stem cells for all cell and tissue types have not yet been found in the adult human. For example, we have not located adult cardiac stem cells or adult pancreatic islet cells.

Secondly, adult stem cells are often present in only minute quantities, are difficult to isolate and purify, and their numbers may decrease with age. For example, brain cells from adults that may be neuronal stem cells have only been obtained by removing a portion of the brain of epileptics, not a trivial procedure.

Any attempt to use stem cells from a patient's own body for treatment would require that stem cells would first have to be isolated from the patient and then grown in culture in sufficient numbers to obtain adequate quantities for treatment.

For some acute disorders, there may not be enough time to grow enough cells to use for treatment. In other disorders, caused by a genetic defect, the genetic error would likely be present in the patient's stem cells. Cells from such a patient may not be appropriate for transplantation.

Research on the early stages of cell specialisation may not be possible with adult stem cells since they appear to be further along the specialisation pathway than pluripotent stem cells. In addition, one adult stem cell line may be able to form several, perhaps 3 or 4, tissue types, but there is no clear evidence that stem cells from adults, human or animal, are pluripotent. In fact, there is no evidence that adult stem cells have the broad potential characteristic of pluripotent stem cells. In order to determine the very best source of many of the specialised cells and tissues of the body for new treatments and even cures, it will be vitally important to study the developmental potential of adult stem cells and compare it to that of pluripotent stem cells.

National Institutes of Health, May 2000