10 
Monitoring Stem Cell Research 
C. Adult (or N on-embryonic) Stem Cells 
Adult stem cells are more differentiated than ES or EG cells, 
but not yet fully differentiated. Like stem cells of embryonic 
origin, they can give rise to lineages of cells that are more spe- 
cialized than themselves. The term “adult" is a bit of a misno- 
mer (“non-embryonic" would be more accurate): these cells 
are found in various tissues in children as well as adults (and 
in fetuses as well), and they have been isolated from umbilical 
cord blood at the time of delivery. Despite its inaccuracy re- 
garding the origin of the cells, the term “adult” helpfully em- 
phasizes that the cells have been partially differentiated. Al- 
though they can give rise to various cell types, these non- 
embryonic stem cells are generally all within the same broad 
type of tissue (for example, muscle stem cells, adipose stem 
cells, neural stem cells). For this reason, it had long been 
thought that they are less flexible than those derived from em- 
bryos or fetal gonads. Yet this presumption has been disputed 
in recent years by those who think that certain forms of adult 
stem cells may be equally or nearly as plastic as non-adult 
stem cells. Indeed, possible exceptions to the generalization 
that adult stem cells give rise only to cell types found within 
their own broad type of tissue have recently been reported 
(though most of these cells may well be shorter-lived than ES 
cells, and, if so, potentially less useful in therapy). This finding 
has ignited a debate about the relative merits of embryonic 
stem cells and adult stem cells: which is more valuable, both 
for research and (especially) for clinical treatment?* 
Research involving adult stem cells raises few difficult ethi- 
cal concerns, beyond the usual need to secure free and fully 
informed consent from donors and recipients, a favorable bene- 
fit-to-risk ratio for all participants in attempts at therapy, and 
protection of privacy. Adult stem cells are less controversial 
* We shall review recent work with both kinds of cells in Chapter 4. Antici- 
pating the implications of that discussion, we may safely say that not 
enough is known to answer this empirical question. Work with both kinds of 
cells seems promising. Some people argue that research with non-embryonic 
stem cells, being a morally unproblematic path, should be given priority. 
Most researchers, meanwhile, support the advancement of work with both 
kinds of cells simultaneously, to explore their potential. 
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