Research and Therapy Developments 
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m. MAJOR EXAMPLES OF HUMAN STEM CELLS 
In this section we discuss major examples of human stem 
cells that meet many of the criteria listed above. Among hu- 
man adult stem cells, we focus on mesenchymal stem cells 
(MSCs),^ multipotent adult progenitor cells (MAPCs),^ and neu- 
ral stem cells, and among human embryonic stem cells, on 
ESC^ and EGC^ cells. For information on the v\hde variety of 
other human stem cell preparations isolated from adult tissues, 
see reference (4) (Appendix K). 
Further research on some of these other adult stem cell 
preparations may demonstrate that they can also be “single 
cell cloned," expanded considerably by growth in vitro with 
retention of normal chromosome structure and number, and 
preserved by freezing and storage at low temperatures. At 
that point, it would be very important to compare the proper- 
ties of these other adult stem cells, and the more differentiated 
cells that can be derived from them, with the already charac- 
terized human embryonic and adult stem cell preparations. 
A. Human Adult Stem Cells 
1. Human Mesenchymal Stem Cells. 
Bone marrow contains at least two major kinds of stem 
cells, hematopoietic stem cells^° that give rise to the red cells 
and white cells of the blood, and mesenchymal stem cells* that 
can be reproducibly isolated and expanded in vitro, and that 
can differentiate in vitro into cells with properties of cartilage , 
bone, adipose (fat), and muscle cells. 
The characteristics (morphology , expressed proteins, and 
biological properties) of these cells have been somewhat diffi- 
cult to specify, because they appear to vary depending upon 
the in vitro culture conditions and the specific cell prepara- 
tion.^^ However, there is a recent report indicating that MSCs, 
if isolated using three somewhat different methods, give rise 
to stem cell preparations whose properties are very similar to 
* The terms "stromal stem cells,” "mesenchymal stem cells," and "mesen- 
chymal progenitor cells” have all been used by different authors to describe 
these cells. 
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