Embryonic stem cells in science and medicine: an invitation for dialogue.

Embryonic stem cells hold tremendous promise both medically and commercially. Researchers anticipate stem cell therapeutics to have an impact on conditions ranging from diabetes to Parkinson's disease. As with many medical therapies based on donated tissues, the shortage of donated egg cells or embryos required to produce the stem cell lines significantly limits the advance of research. A number of factors affect the supply of donated material, including federal and state issues and perceived ethical constraints. Furthermore, similar to the donation of other living tissue, donation of raw material is not without risk and inconvenience, particularly for the egg donor. The first article of this 2-part series provides an overview of stem cells and the current regulatory regime in the United States regarding pluripotent stem cells. In the second article, we examine the similarities and differences compared with other medical therapies that require donated human material, such as biologics (plasma and other blood-derived products) and organs, as well as the current state of the art and certain ethical considerations, such as origin of the cells and risk to the donor.