Research and Therapy Developments 
131 
A, Will Stem Cell-Based Therapies Be Limited by Immune 
Rejection? 
Much of the impetus for human stem cell research comes 
from the hope that stem cells (or more likely, differentiated 
cells derived from them) will one day prove useful in cell 
transplantation therapies for a variety of human diseases. Such 
cell transplantation would augment the current practice of 
whole organ transplantation. To the extent that the healing 
process works with in vitro derived cells, the need for organ 
donors and long waiting lists for organ donation might be re- 
duced or even eliminated. 
Will the recipient (patient) accept or reject the transplanted 
human cells? In principle, the problem might seem avoidable 
altogether: adult stem cells could be obtained from each indi- 
vidual patient needing treatment. They could then be grown or 
modified to produce the desired ( autologous and hence rejec- 
tion-proof) transplantable cells. But the logistical difficulties in 
processing separate and unique materials for each patient 
suggest that this approach may not be practical. The cost and 
time required to produce sufficient numbers of well- 
characterized cells suitable for therapy suggest that it v\hll be 
cells derived from one or another unique stem cell line that will 
be used to treat many (genetically different) individual pa- 
tients ( allogeneic cell transplantation ). 
When allogeneic organ or tissue transplantation is currently 
done using, for example, bone marrow, kidney, or heart, pow- 
erful immimosuppressive drugs — carrying undesirable side 
effects — ^must be used to prevent immunological rejection of 
the transplanted tissue.® Without such immunosuppression, 
the patient’s T-lvmphocvtes and natural killer (NK) cells recog- 
nize surface molecules on the transplanted cells as “foreign” 
and attack and destroy the cells. Also, in whole organ trans- 
plantation donor T-lymphocytes and NK cells, entering the re- 
cipient with the transplanted organ, can also destroy the tis- 
sues of the transplant recipient (called “graft versus host" dis- 
ease). 
Are the differentiated derivatives of human stem cells as 
likely to incite immune rejection, when transplanted, as are 
solid organs? Do their surfaces carry those protein antigens 
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