The undifferentiated stem cells from the inner cell mass of the blastocyst that are grown in the Petri dish for a period of months are referred to as an embryonic stem cell line.

President Bush in 2001 approved government-funded research on what were believed to be 78 existing embryonic stem cell lines. However, there were far fewer than 78 identified for use. In reality, there are only 11 lines now available on the National Institutes for Health (NIH) website, and their quality is questionable. For example, they were grown on mouse feeder lines and may be contaminated with mouse viruses and proteins. Because there are so few lines, they are not genetically diver