The National Institutes of Health is slightly expanding its definition for what constitutes a human embryonic stem cell. Currently, for purposes of including cells in its stem cell registry, NIH guidelines define the cells as "derived from the inner cell mass of blastocyst stage human embryo." As proposed tomorrow in the Federal Register, the definition will cover "early stage embryos up to and including" the blastocyst stage.
The change has come primarily in response to an application by Advanced Cell Technology (ACT) of Worcester, Massachusetts. "We came to understand recently that there was interest in deriving cells from earlier-stage embryos," says NIH's Lana Skirboll. ACT wants to list on the registry five cell lines derived from the earlier, morula stage. Skirboll says that, in addition, three lines submitted by Harvard Medical School's George Daley were derived from embryos that hadn't reached blastocyst stage. Approval for them has been put on hold pending acceptance of the revised definition.
So far the registry has approved 40 lines. The change is a small one, Skirboll says; There is no change in ethical guidelines for deriving cells.