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Monitoring Stem Cell Research 
This paper will not attempt to review the literature related to 
hematopoietic stem cells, i.e., the bone marrow stem cell that is the 
immediate precursor for blood cells, and the formation of typical 
blood cells. Nor will this paper review the substantial literature 
regarding clinical use of bone marrow or bone marrow stem cell 
transplants for hematopoietic conditions such as various cancers and 
anemias, nor the striking clinical results seen for conditions such as 
scleromyxedema, multiple sclerosis, systemic lupus, arthritis, 
Crohn’s disease, etc.^ In these instances, the stem cells are used 
primarily to replace the hematopoietic system of the patient, after 
ablation of the patient’s own bone marrow hematopoietic system. 
Finally, multipotent adult progenitor cells (MAPC’s), a bone marrow 
stem cell that has shown significant abilities at proliferation in 
culture and differentiation into other body tissues,^ have been 
reviewed by Dr. Catherine Verfaillie in a separate paper for the 
President’s Council on Bioethics, and the reader is directed to that 
review for more information. 
Key questions regarding adult stem cells are: (1) their 
identity, (2) their tissue source of origin, (3) their ability to form other 
cell or tissue types, and (4) the mechanisms behind such changes in 
differentiation and effects on tissues and organs. Historically only a 
few stem cells were recognized in humans, such as the 
hematopoietic stem cell which produces all of the blood cell types, 
the gastrointestinal stem cell associated with regeneration of the 
gastrointestinal lining, the stem cell responsible for the epidermal 
layer of skin, and germ cell precursors (in the adult human, the 
spermatogonial stem cell.) These stem cells were considered to have 
very limited repertoires, related to replenishment of cells within their 
tissue of origin. These limitations were considered to be a normal 
part of the developmental paradigm in which cells become more and 
more restricted in their lineage capabilities, leading to defined and 
specific differentiated cells in body tissues. ’Thus, discovery of stem 
cells in other tissues, or with the ability to cross typical lineage 
boundaries, is both exciting and confusing because such evidence 
challenges the canonical developmental paradigm. 
STEM CELL MARKERS 
Identification of cells typically relies on use of cell surface 
markers — cellular differentiation (CD) antigens — ^that denote the 
expression of particular proteins associated vdth genomic activity 
related to a particular differentiation state of the cell. Identification 
PRE -PUBLICATION VERSION 
