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Monitoring Stem Cell Research 
that will be recognized as “foreign”? Experiments have been 
done to examine human ESC and MSC preparations growing in 
vitro for the expression of surface molecules known to play im- 
portant roles in the immune rejection process. Drukker and 
coworkers^® showed that embryonic stem cells in vitro express 
very low levels of the immimologically crucial major histocom- 
patibility complex class I (MHC-I) proteins on their cell surface. 
The presence of MHC-I proteins increased moderately when 
the ESCs became differentiated, whether in vitro or in vivo. A 
more pronoimced increase in MHC-I antigen expression was 
observed when the ESCs were exposed to gamma-interferon , a 
protein produced in the body during immune reactions. Thus, 
under some circumstances, human ESC-derived cells can ex- 
press cell surface molecules that could lead to immune rejec- 
tion upon allogeneic transplantation. 
Similarly, Majumdar and colleagues showed that human 
mesenchymal stem cells in vitro express multiple proteins on 
their cell surfaces that would enable them to bind to, and in- 
teract with, T-lymphocytes. They also observed that gamma- 
interferon increased expression of both human leukocyte anti- 
gen (HLA) class I and class II molecules on the surface of these 
MSCs."^° These results indicate that it will probably not be pos- 
sible to predict, solely on the basis of in vitro experiments, the 
likelihood that transplanted allogeneic MSCs would trigger 
immune rejection processes in vivo. 
Many further studies in this area are badly needed. At this 
time there is insufficient information to determine which, if 
any, of the approaches to get around the rejection problem will 
eventually prove successful. 
B. Case Study: Stem Cells in the Future Treatment of Type-1 
Diabetes? 
1. The Disease and Its Causes. 
The human body converts the sugar glucose into cell energy 
for heart and brain functioning, and indeed, for all bodily and 
mental activities. Glucose is derived from dietary carbohy- 
drates, is stored as glycogen in the liver, and is released again 
when needed into the bloodstream. A protein hormone called 
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