2 
Monitoring Stem Cell Research 
both the policy and the research are still in their infancy, the 
Council is now ready to give the President and the public an 
update on this important and dynamic area of research. 
This report is very much an “update." It summarizes some 
of the more interesting and significant recent developments, 
both in the basic science and medical applications of stem cell 
research and in the related ethical, legal, and policy discus- 
sions. It does not attempt to be a definitive or comprehensive 
study of the whole topic. It contains no proposed guidelines 
and regulations, nor indeed any specific recommendations for 
policy change. Rather, it seeks to shed light on where we are 
now — ethically, legally, scientifically, and medically — in order 
that the President, the Congress, and the nation may be better 
informed as they consider where we should go in the future. 
I. WHAT ARE STEM CELLS, AND WHY IS THERE 
CONTENTION ABOUT THEM? 
The term “stem cells" refers to a diverse group of remark- 
able multipotent cells. Themselves relatively undifferentiated 
and unspecialized, they can and do give rise to the differenti- 
ated and specialized cells of the body (for example, liver cells, 
kidney cells, brain cells). All specialized cells arise originally 
from stem cells, and ultimately from a small number of embry- 
onic cells that appear during the first few days of develop- 
ment.* As befits their being and functioning as progenitor 
cells, all stem cells share two characteristic properties: (1) the 
capacity for unlimited or prolonged self-renewal (that is, the 
capability to maintain a pool of similarly undifferentiated stem 
cells), and (2) the potential to produce differentiated descen- 
dant cell types. As stem cells within a developing human em- 
bryo differentiate in vivo, their capacity to diversify generally 
becomes more limited and their ability to generate many dif- 
ferentiated cell types generally becomes more restricted. 
* These cells are grouped together as the “inner cell mass” of the embryo, at 
the blastocyst stage of its development. Readers should consult the Glossary 
for definitions of technical terms and Appendix A for an illustrated guide to 
the embryonic developments referred to in this report. 
PRE -PUBLICATION VERSION 
