The advance is seen as a breakthrough that will enable scientists eventually to use the stem cells to repair diseased or damaged tissue. It likely also will facilitate the use of the cells for studying how diseases originate, which could lead to insights about cures and treatments.

Because embryonic stem cells have the capability to give rise to all the different cell types found in the human body, scientists think they can be harnessed to regenerate specific regions of the body, such as the brain or heart. The trick is determining the precise combination of chemical compounds needed to trigger the stem cells to become a specific cell type.

Now, Emmanuel Baetge of CyThera, in San Diego, and colleagues report in the December issue of Nature Biotechnology they have figured out a key piece of that puzzle and come up with a mix that spurs the stem cells to develop into endoderm -- a layer found in developing embryos that gives rise to the thyroid, thymus, lungs, liver, pancreas and the lining of the respiratory and digestive tracts.

"We have described an approach to produce highly enriched cultures of definitive endoderm from (human embryonic stem cells)," Baetge's team wrote.

The technique is "a critical step in generating scientifically and therapeutically useful cells of the definitive endoderm lineage, such as (liver cells) and pancreatic endocrine cells," the scientists added.

"It basically shows human embryonic stem cells have the capacity to make this lineage and all the resulting cells that come from that that make up all these organs," Baetge told United Press International.

"If you were to use human embryonic stem cells to make products that treat disease, such as diabetes or liver failure, you'd have to go through the endoderm stage to get to it," he added.

Baetge's company, CyThera, is focused on using stem cells to generate an unlimited supply of islet cells, which are found in the pancreas and produce insulin, to treat diabetes.

Outside scientists also hailed the advance.

"Endoderm is one of the most therapeutically important and most difficult to obtain, so this is certainly a very important step," Dr. Robert Lanza, vice president of medical and scientific development at Advanced Cell Technology, told UPI. Advanced Cell, a biotech company based in Worcester, Mass., is seeking to develop medical therapies from stem cells.

Beyond the direct therapeutic applications, the finding also has "massive implications" for developing new drugs and understanding human development, Baetge said.

Pharmaceutical companies could use the technique to generate an unlimited supply of human tissues, such as liver cells, for screening potential new drugs, he said. The cells could also be used to study cancer and "all kinds of aspects of what might go wrong as a human cell is developing," he added.

The scientific consensus is embryonic stem cells hold great potential for generating insights and even treatments for disease, but the research is controversial because it involves the destruction of an embryo, which some, including President Bush, equate with taking a human life.

Bush has limited federal funding of the research to stem-cell lines that already were in existence in 2001. This meant CyThera had to use private funds for its research, because three of the eight stem-cell lines they used were not on the list approved by the administration.

The administration's policy has been criticized for hampering progress in the stem-cell field, and both Congress and the scientific community have begun taking steps to circumvent it.

Meanwhile, scientists recently announced new methods for obtaining stem cells that may avoid some of the ethical hurdles associated with conventional techniques, but it remains unclear if the techniques, which were developed using mice cells, will hold true for human cells. In addition, these techniques are not intended to replace conventional techniques but rather to provide an alternative for those who object to the destruction of embryos.

The House in May passed the Stem Cell Research Enhancement Act, which would relax some of Bush's limitations on stem-cell research and allow federal funding to go towards research involving surplus embryos from fertilization clinics that would otherwise be destroyed. The Senate appears poised to pass the legislation, but a vote on it has been delayed until next year, and Bush has said he will veto it.

Lanza said Baetge's research underscores the limiting impact of Bush's policy. He noted that different stem-cell lines reacted differently to the technique and said Advanced Cell found the same thing with some of their research.

Each stem-cell line is unique and has its own set of characteristics, "so we need access to more and better quality stem-cell lines," Lanza said. "Until that happens, this field is going to hobble along rather than sprint to the goal post," he added.

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