Embryonic stem cells may be the new kids on the block, but their promising attributes are attracting much attention.

http://www.ama-assn.org/sci-pubs/amnews/pick_01/hlsb0813.htm

Aug. 13, 2001
By Susan J. Landers, AMNews staff.

Washington -- Regardless of whether stem-cell research moves forward with embryonic stem cells or adult stem cells, with public or private funding, recent results have sparked enough enthusiasm, controversy and debate to carry the field forward for a long time.

If stem cells live up to their promise, they could dramatically improve physicians' odds of defeating a long list of serious conditions that include diabetes, Parkinson's disease, end-stage kidney disease, liver failure, heart disease, multiple sclerosis, spinal cord injury and stroke.

But, the promise of embryonic stem cells is not only a long way from being realized, it is also tempered by problematic ethical issues.

Meanwhile, the difficulties of working with adult stem cells has dimmed researchers' zeal.

Still, the potential of stem-cell research can be tantalizing.

"Over 3,000 people die every day in the United States from diseases that may someday be treatable as a result of stem-cell research," according to a report by the Progressive Policy Institute, a Washington, D.C.,-based think tank.

While much of the recent interest has been sparked by embryonic stem cells, which were first isolated from embryos only three years ago, the momentum for research on adult stem cells, which has been conducted for many years, has waned a bit.

Much remains unknown. "So far, adult stem cells have proven to be very different from embryonic stem cells," ventures Tony Mazzaschi, associate vice president for research at the American Assn. of Medical Colleges. He notes that the AAMC supports research on both types of stem cells. The AMA also strongly supports all stem-cell research, as do numerous other medical groups.

It isn't hard to find research success stories.

Dramatic findings released in mid-July by Johns Hopkins University researcher John Gearhart, MD, offered videotaped proof that previously paralyzed mice and rats regained some ability to use their legs after being injected with embryonic stem cells.

At about the same time, researchers in London revealed that they had coaxed adult stem cells found in bone marrow to develop as kidney cells.

The National Institutes of Health released a report on July 18 that also cites the promise of both types of stem-cell research.

All stem cells, whether derived from adults, embryos or fetuses, can, under certain conditions, reproduce themselves for long periods of time. They can also give rise to specialized cells that make up the tissues and organs of the body.

Where the similarities end

Embryonic stem cells have certain attributes that, so far at least, have not been found in adult stem cells. For one thing, embryonic stem cells are pluripotent, whereas adult stem cells are believed to have a more limited range.

In addition, "As far as we know, [embryonic stem cells] can replace themselves forever, unlike adult stem cells," said James Thompson, PhD, a developmental biologist at the University of Wisconsin-Madison and one of the first two scientists to isolate stem cells from human embryos. Dr. Thompson spoke at a National Academies of Science workshop in June.

Dr. Thompson derives embryonic stem cells from four- to five-day-old embryos called blastocysts, which are donated by couples undergoing in vitro fertilization. The embryos, which are destroyed in the process of extracting stem cells, are said to be extras and destined to be destroyed in any case.

There appear to be only two sources for human pluripotent stem cells: those isolated and cultured from early human embryos and those cultured from fetal tissue destined to be part of the gonads.

Dr. Gearhart, who takes honors with Dr. Thompson as the other researcher to have isolated human embryonic stem cells, uses the second approach to develop his stem cells, an approach that, so far, seems to have escaped controversy.

However, the destruction of the early stage embryos has sparked a strong debate over whether federal funding should support such research. President George W. Bush was still struggling with the issue at press time.

Congress is also divided on the issue.

But adult stem cells are free of the current debate. And those that oppose the destruction of the blastocyst in order to obtain embryonic stem cells gladly point to the successes of adult stem-cell research and the need to continue.

To date, adult stem cells have been identified in brain, bone marrow, peripheral blood, blood vessels, skeletal muscle, epithelia of the skin and digestive system, cornea, dental pulp of the tooth, retina, liver and pancreas.

Although they are found in many sites, they are rare and difficult to identify, isolate and purify, notes the NIH report.

But David Stevens, MD, executive director of the Christian Medical Assn. and an opponent of embryonic stem-cell research, believes the promise of adult stem-cell research is being unfairly overlooked.

"Adult stem cells have been used in rebuilding ears, tracheas in humans, and even have been used to regenerate heart tissue in mice," he said.

As Dr. Stevens sees the debate, "If we have two paths of promising research and one has ethical issues and the other does not, which one should we pursue? It seems to me we should pursue the one without the ethical problems."

He also points out potential difficulties with embryonic stem cells. "The biggest benefit of embryonic stem cells is that they can differentiate into so many different types of cells. But that's their biggest problem, too. How do you direct them?"

A federal ban on research would mean the NIH, the lead supporter of biomedical research, and an agency currently enjoying an increased funding level, would be prohibited from supporting embryonic stem-cell research. Privately funded research could continue, but outside the sphere of NIH guidelines, leading some to fear that research standards would suffer.

The funding debate has dragged on for many months now. In January, the AMA joined with more than 100 other medical groups in urging the president to release funding. The groups said, "Given the great hope that stem-cell research provides to those who are suffering or dying from devastating illnesses, we urge you to allow this research to move forward with federal support."

Weblink

NIH Stem Cell Information page (http://www.nih.gov/news/stemcell/)

AMA Genetics and Molecular Medicine page (http://www.ama-assn.org/ama/pub/category/1799.html)