24 February 2010
The official definition of human embryonic stem (HES) cells in US National Institutes of Health (NIH) guidelines is to be broadened from those ‘derived from the inner cell mass of blastocyst stage human embryo’ (ie. from embryos that have reached the blastocyst stage at four or five days old, 70-100 cells), to include also those derived from earlier stage embryos.
Dr Lana Skirboll, director of the Office of Science Policy of the NIH, reportedly said: "We are making what I think is a relatively small technical change to the definition of human embryonic stem cells…This changes none of the ethical requirements in the guidelines" (see Reuters news). This move was prompted by an application from a commercial source to list cell lines derived from eight-cell stage embryos, and will make some commercial and academic research programmes potentially eligible for government funding.
Derivation of HES cells from a cell taken from an eight-cell stage embryo could possibly allow implantation and normal development of the remaining seven-cell embryo. This is what happens in pre-implantation prenatal diagnosis (PGD); one cell is removed for genetic analysis and, if healthy, the seven-cell embryo is implanted and can grow into a normal fetus.