The US National Institutes of Health this week added three more human embryonic stem cell lines to its registry of lines eligible for federal funding. But be sure to read the fine print before you start ordering these cells for your own experiments.

Following the agency’s policy decision to honor any restrictive language included in informed consent forms, NIH director Francis Collins ruled that one of the newly approved cells lines — called H1 — cannot be used for research that mixes the cells with any intact embryos, human or otherwise. The stem cell line also cannot contribute to making whole embryos by any method.

“This goes farther than the current NIH policy,” which restricts mixing human embryonic stem cells with primate embryos but not other animals, Lana Skirboll, director of policy at NIH, said today at a press conference. The two other cell lines were given the go-ahead without any catches.

In December, Collins approved the first 40 lines on the list, but 27 of these also came with the limitation that they could only be used to study diabetes-related pancreatic cells. Now, researchers will have to be especially prudent that they don’t carry out the wrong experiments with the wrong cells.

The H1 cell line, which was derived by the University of Wisconsin–Madison’s James Thomson, is one of the most widely used in the field. It is also the first line to be approved under the NIH’s new guidelines that was also eligible for funding under former President George W. Bush’s administration.

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