Research and Therapy Developments 
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therapies for osteogenesis imperfecta .^^ metachromatic leu- 
kodystrophy . and Hurler syndrome . These last two studies 
are of great interest, since allogeneic MSCs were used and no 
serious adverse immune reactions were noted. 
2. Multipotent Adult Progenitor Cells (MAPCs). 
Verfaillie and coworkers recently described the isolation of 
MAPCs from rat, mouse, and human bone marrow [see (3) and 
references cited therein]. Like MSCs, MAPCs can also be dif- 
ferentiated in vitro into cells with the properties of cartilage, 
bone, adipose, and muscle cells. In addition, there is evidence 
for the in vitro differentiation of human MAPCs into functional, 
hepatocvte -like cells, a potential that has not so far been 
shown for MSCs. There is increasing interest in MAPCs, both 
as potential precursors of multiple differentiated tissues and, 
ultimately, for possible autologous transplantation therapy. 
The relationship between human MSCs and the human 
MAPCs described by Verfaillie and coworkers [see (3)] needs 
to be clarified by further research. Both kinds of cells are iso- 
lated from bone marrow aspirates as cells that adhere to plas- 
tic. Each can be differentiated in vitro into cells with cartilage, 
bone, and fat cell properties. They express several of the same 
cell antigens , but are reported to differ in a few others.^ 
MAPCs have to be maintained at specific, low cell densities 
when grown in vitro, otherwise they tend to differentiate into 
MSCs.^ It remains important that the isolation and properties 
of MAPCs be reproduced in additional laboratories. 
3. Human Neural Stem Cells. 
The nervous system is made up of three major types of cells; 
neurons or nerve cells proper, and two kinds of supporting or 
glial cells ( oligodendrocyte . astrocyte ). Stem cells capable of 
differentiating into one or more of these neural cell lineages 
can be isolated from brain tissue (particularly the olfactory 
bulb and lining of the ventricles)^'*'^^ and grown in vitro. In the 
presence of purified growth-factor proteins, the population of 
cells can be expanded by growth in vitro as round clumps of 
cells called neurospheres. However, many neurospheres 
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