Stem cells from adults and embryos both show enormous promise for treating an array of diseases but at this early stage, cells from days-old embryos appear to offer certain key advantages, according to a National Institutes of Health study being released today. Embryonic stem cells are more plentiful and therefore easier to extract, can be grown and made to multiply in the laboratory more easily and appear to have the uncanny ability to develop into a much wider array of tissues, the report concludes.

Stressing that the work remains very preliminary, the report states that the only way to address the many uncertainties around stem cells -- including how well any cells might work for treating diseases and which ones might work best -- is to conduct more research on both types.

As President Bush struggles to decide whether to permit federal funding of the research, the eagerly awaited report could undercut two possible compromises -- funding only work on adult cells or only work with the handful of existing embryonic cell lines. The report states that the only way to explore the cells' full potential is by examining many different cell lines and both types of cells.

"To date it is impossible to predict which stem cells -- those derived from the embryo, the fetus, or the adult -- or which methods for manipulating the cells, will best meet the needs of basic research and clinical applications. The answers clearly lie in conducting more research," according to a 12-page summary of the report.

The 200-page report, requested by Health and Human Services Secretary Tommy G. Thompson, is the result of an exhaustive review of the scientific literature on the subject and represents the most authoritative assessment to date of the therapeutic potential and equally large uncertainties surrounding the rapidly changing field.

The report comes as the debate over the research continues to intensify. Absent a presidential decision, lawmakers and advocates on both sides have aggressively joined the fight.

Proponents argue that federal funding is necessary to fully explore whether the cells could provide treatments for many diseases. Opponents object to the research because it requires destroying what they consider potential human life. The cells are primarily obtained from surplus embryos from fertility clinics.

The NIH report is due to be released at a Senate hearing today being convened by two of the most ardent proponents of federally funded research on all types of stem cells: Sen. Tom Harkin (D-Iowa) and Arlen Specter (R-Pa.).

Also at the hearing, Sen. Bill Frist (R-Tenn.) is expected to declare his position on stem cell research. Yesterday, Capitol Hill buzzed with speculation over what his position will be because Bush aides have signaled the president is looking to the heart surgeon for guidance -- and perhaps some political cover.

"I feel very encouraged about Bill's position," said Sen. Gordon Smith (R-Ore.) who spoke in favor of embryonic stem cell research despite his opposition to abortion.

"This is about giving life to compassionate conservatism," he said. "Life does not begin in a petri dish; it begins with a mother. Being pro-life means helping the living as well."

Under guidelines developed by the Clinton administration, government scientists would be permitted to conduct experiments on embryonic cells as long as the researchers did not participate in destroying embryos. Researchers would only have access to the cells after couples decided they did not want the embryos themselves and did not want to donate them to another couple.

Although Thompson supports embryonic stem cell research, the report by his agency "does not make recommendations pertaining to the policies governing federal funding of such research," the authors wrote. It also makes no effort to analyze the ethical issues raised by the research.

The NIH report does detail apparent shortcomings in adult stem cells, notably that those cells -- commonly taken from an individual's blood or bone marrow or skin -- do not have the flexibility to develop into all types of tissue."

Current evidence indicates that the capability of adult stem cells to give rise to many different specialized cell types of more limited than that of embryonic stem cells," the report states. Adult stem cells are rare, difficult to identify and there may be "insufficient numbers of cells available for transplantation."

The report notes, however, that there are possible limitations with embryonic cells as well. For example, there is some evidence that the cells could form tumors. "It is not known whether similar results are observed with adult stem cells," the report states.

The best way to fully understand the potential of different types of cells is to develop many different cell lines."

There have been very few studies that compare various stem cells' lines with each other. It may be that one source proves better for certain applications, and a different cell source proves better for others," the report states.

At the first of two dueling congressional hearings this week, parents of children born from surplus embryos that had been "adopted" from fertility clinics testified against funding the research. Mark and Luke Borden, both 9 months old, would not be alive today if scientists had the opportunity to experiment on their embryos, their parents said.

As he stood holding the two squirming toddlers, John Borden equated embryonic stem cell research to the killing of a burgeoning life. "Which one of my children would you kill?" he asked. "Which one would you choose to take?"

Nearly three hours later, 12-year-old twins Mollie and Jackie Singer spoke in support of the research. Describing her eight years with juvenile diabetes -- "21,000 shots, 28,000 finger pricks and open heart surgery" -- Mollie implored the policymakers to do everything in their power to pursue treatments and cures of illnesses such as hers.

"I don't want Jackie or anyone to go through what I've been through," she said.




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