Appendix I. 
Current Progress in 
Human Embryonic Stem Cell Research 
TENNEILLE E. LUDWIG, PH.D. and 
JAMES A. THOMSON, PH.D 
Wisconsin National Primate Research Center, University of 
Wisconsin-Madison 
The immortality and potentially unlimited developmental 
capacity of human embryonic stem (ES) [1] cells ignite the 
imagination. After months or years of growth in culture dishes, these 
cells retain the ability to form cell types ranging from heart muscle to 
nerve to blood — possibly any cell in the body. Because of their 
unique developmental potential, human ES cells have widespread 
implications for human developmental biology, drug discovery, drug 
testing, and transplantation medicine. Indeed, human ES cells 
promise an essentially unlimited supply of specific cell types for in 
vitro experimental studies and for transplantation therapies for 
diseases such as heart disease, Parkinson's disease, leukemia, and 
diabetes. 
The derivation of a human ES cell line destroys a human 
embryo. Thus, the derivation of human ES cells resurrected a fierce 
controversy over human embryo research in the United States, a 
controversy originally created by the development of human in vitro 
fertilization decades ago, but never completely resolved. In 
particular, the derivation of human ES cells led to a re-examination of 
the role of federal funding of human embryo research. In response to 
the intense public interest. President George W. Bush reviewed the 
potential of human ES cell research to improve the health of 
Americans. In his national address on August 9, 2001, he stated 
“Federal dollars help attract the best and brightest scientists. They 
ensure new discoveries are widely shared at the largest number of 
research facilities, and the research is directed toward the greatest 
public good." On that basis, he directed federal funding to "explore 
the promise and potential of stem cell research," including, for the 
first time, human ES cell research. However, the President went on 
to restrict federal funding to research that used only those human ES 
cell lines derived prior to his address on August 9, 2001. This paper 
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