BRUSSELS, Belgium - Human embryonic stem cells could be used to identify factors involved in differentiation and proliferation of committed embryonic progenitor cells. And because they can in principle serve as an unlimited source of any cell type in the body, they could yield highly effective in vitro models for use in drug discovery programs, and provide a renewable source of cells for use in transplantation therapy.

That opinion was offered by Outi Hovatta, of the Karolinska Institute in Stockholm, on Monday at the start of a round table in Brussels on the ethical aspects of human stem cells research and uses.

"These cell lines should be useful in the future studies of human developmental biology, drug discovery, and transplantation medicine," she said.

Her unit has initiated a project to culture human embryonic stem cell lines, characterize them for applications in research, and develop them for possible clinical applications. In April she received ethical authorization to culture cells derived from the inner cell mass of IVF-derived human blastocysts - and questions raised over whether this could be regarded as culturing of the human embryo beyond 14 days have been allayed since the inner cell mass is only part of the embryo.

Upcoming work will include confirming the stem cells nature of the cell lines and culturing them for prolonged periods under good manufacturing practice conditions, because of the potential clinical application at a later stage. In later projects, the ability of these cells to differentiate in a controlled way to stem cells of different organ systems will be studied, in collaboration with groups already using such cells.

Didier Houssin, professor of surgery at the Paris Graft Institute, another enthusiast for stem cell research, acknowledged that there are real questions to be answered in using this technology. "If it were only a question of research efforts, funding and precautions before any clinical use, nothing would distinguish the reflection on future medical uses of human stem cells from the reflection continually conducted on medicines or medical devices. But there is a third party at stake here - not the living or deceased donor that is at stake in transplants, but the use of a human embryo for research carried out in the name of what will certainly be a very distant therapeutic application, with all the ethical questions that raises."

And Alastair Campbell, professor of ethics in medicine at Bath University in the UK, said he hoped for "some meeting of minds on how this area should be legislated for," despite the widely differing views on its future. "It is essential we keep discussing the issue," he said. "I am opposed to too rapid a conclusion about how the valuation is to be made. I do not think we should close off all possibilities of progress in the science by some kind of wholesale ban." He suggested there was a need to develop a "more sophisticated moral vocabulary."

The round table, organized by Noelle Lenoir, the president of the European Commission's advisory group on ethics in science and the new technologies, was part of its preparatory work for an opinion it is developing on stem cell research, due for publication later this year.