An embryonic stem cells — made to be born? Credit: DAVID SCHARF/SCIENCE FACTION/CORBIS

US stem-cell researchers are applauding draft guidelines released by the National Institutes of Health (NIH) last week to govern federally funded research on human embryonic stem-cell lines. Some, however, say the provisional rules are still too restrictive because they would exclude lines derived from embryos created for research purposes.

The provisional rules come 39 days after President Barack Obama signed an executive order freeing up federal money for such research. They would limit federal funding to work on stem-cell lines derived from embryos created by in vitro fertilization (IVF) solely for reproductive purposes, and no longer needed for that purpose. Researchers would have to document that parents had voluntarily donated the embryos, without inducements and without researcher influence.

Disappointingly for some researchers, the guidelines explicitly disqualify from funding any stem-cell lines derived from embryos created for research purposes, whether by standard IVF methods or by somatic-cell nuclear transfer. The draft guidelines also forbid funding for lines derived through parthenogenesis, a form of asexual reproduction in which an unfertilized egg is developed into an embryo.

The guidelines, if adopted as issued last week, could create an immediate problem for researchers already working on the score of lines approved for federal funding in August 2001 by former president George W. Bush. Of those lines, "not all are likely to be eligible for continued federal funding" under the new draft guidelines, says Thomas Murray, president of the Hastings Center, a bioethics think tank in Garrison, New York. "I would counsel the NIH to consider creating an exception for these cell lines if they continue to have very significant scientific value," he says.

Others go further. The agency's informed consent requirements are "fine going forwards. But I think they are going to have to loosen those expectations a little bit for [all] pre-existing lines," says Sean Morrison, director of the University of Michigan Center for Stem Cell Biology in Ann Arbor.

The NIH is publishing its proposed guidelines this week in the Federal Register, kicking off a 30-day public comment period. It has until 7 July to finalize the guidelines.

"This represents a great expansion in opportunity for scientists doing research in this field," says Raynard Kington, acting director of the agency based in Bethesda, Maryland. Defending its decision to exclude lines derived from embryos created for research purposes, he says: "We don't believe that there is yet even consensus within the scientific community that would warrant going to the next step."

Once the guidelines are finalized, the agency will periodically revisit them to see if adjustments are needed to reflect evolving science.

The NIH estimates that more than 760 human embryonic-stem-cell lines exist, and Kington says he expects "many" will meet the final eligibility standards.

Review and funding of current applications for stem-cell research proposals will be deferred until the final guidelines are issued. At that point, researchers will have the opportunity to modify their applications to comply with the guidelines before funding decisions are made.

Mark Kay, a geneticist and stem-cell researcher at Stanford University School of Medicine in California, says he would have liked to see the guidelines embrace stem cells derived outside the reproductive context. Still, he says, the draft effort "is a step in the right direction".

Meri Firpo, who uses stem cells in diabetes research at the University of Minnesota in Minneapolis, says that "there are issues that probably need clarifying". Among them, she says, is whether lines derived from embryos created from donated sperm or ova would qualify. They do not under guidelines adopted in the past by the US National Academies.