Some background is necessary.
The ban on federal funding of human embryo research became public law in 1997. The ban is transitory in the sense that it is revisited each year when the language of the NIH appropriations bill is considered. Among several criticisms of the NIH embryo panel's position was lack of evidence that embryo research would yield clinical benefits. PSCs are more specialized than the totipotent cells in the human blastocyst, each of which can develop into a total individual. Also, John Gearhart's group at Johns Hopkins derived PSCs from tissue of aborted fetuses at 5 to 9 weeks after fertilization and grew these cells into a wide variety of differentiated cell types.