Four months after an executive order from US President Barack Obama, stem cell funding guidelines issued by the US National Institutes of Health (NIH) trulyended the 2001 restriction limiting federal funding to research involving just 21 usable human embryonic stem cell lines.

The rules, which went into effect on 7 July, call for a registry of fundable lines. Human embryonic stem cell lines created going forward will be allowed if they are derived from unused embryos created through in vitro fertilization and given by donors who have undergone a thorough informed consent process.

Many of the nearly 700 lines that have already been created with private funding will be reviewed by an advisory committee. If they meet guidelines held by institutions such as the International Society for Stem Cell Research, the lines will be grandfathered in and allowed, even if they don't fulfill all of the current NIH regulations.

The guidelines also open funding to disease-specific lines, but they do not permit lines that were created by somatic cell nuclear transfer or parthenogenesis—techniques that could be used for cloning human cells.

“Now, we have to hope for two things,” says Geoff Lomax, a lead member of the Interstate Alliance on Stem Cell Research. “The first is that this review process works in an expedient way. The second is that, down the road, we can incorporate intelligent guidelines for techniques that, while scary if misunderstood, are important avenues of research.”