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Monitoring Stem Cell Research 
cells and their potential fates and possible uses.^® They in- 
clude the following: 
• What is the most effective way to isolate and grow 
ESCs? 
• How is the self-renewal of ESCs regulated? 
• Are all ESC lines the same? 
• How can ESCs be genetically altered? 
• What controls the processes of ESC differentiation? 
• What new tools are needed to measure ESC differentia- 
tion in vitro and in vivo? 
V. HUMAN STEM CELLS AND THE TREATMENT OF 
DISEASE 
A major goal of stem cell research is to provide healthy dif- 
ferentiated cells that, once transplanted, could repair or re- 
place a patient's diseased or destroyed tissues. In pursuit of 
this goal, one likely approach would start by isolating stem 
cells that could be expanded substantially in vitro. A large 
number of the cultivated stem cells could then be stored in the 
frozen state, extensively tested for safety and efficacy as out- 
lined above, and used as reproducible starting material from 
which to prepare differentiated cell preparations that will ex- 
press the needed beneficial properties when they are trans- 
planted into patients with specific diseases or deficiencies. 
To make more concrete both the potential of this approach 
and the obstacles it faces, we will summarize, as a case study 
example, some current information on the properties of cells 
derived from human stem cell populations that have been used 
in an animal model of Type-1 diaibetes. But before doing so, we 
discuss an obstacle to any successful program of stem cell- 
based transplantation therapy: the problem of immune rejec- 
tion of the transplanted cells. 
PRE -PUBLICATION VERSION 
