Abstract
It is rare that a field of scientific research can simultaneously represent a domain of fundamental discovery in human biology and potentially have major effects on human health and the quality of life. Human embryonic stem cells serve not only as a resource for basic research, but also as the starting material for the development of cell-based therapies. Formidable scientific challenges face those who aim to develop cell-based therapies. It will take the efforts of many scientists and clinicians in a variety of disciplines to bring this endeavor to fruition. Of immediate importance and concern is whether or not we have sufficient starting material for the initial phases of this research.