Appendix J. 
305 
studies aimed at determining what level of HLA-mismatch will be 
tolerated in transplantations, whether tolerization via hematopoietic 
engraftment from MAPC will be required. As is also the case for 
other extensively cultured cells, we will need to further determine if 
prolonged expansion leads to genetic abnormalities in cells that 
might lead to malignancies when transplanted in vivo. 
As a final remark, MAPC appear to have pluripotent potential 
both in vitro and in vivo. Furthermore, they appear to proliferate 
without obvious senescence when maintained under very stringently 
controlled culture conditions. Because of these reasons, some have 
argued that they might be a viable alternative to ES cells. However, 
at this stage of the research, I feel that such a conclusion is 
premature. Whether MAPC have equal longevity as ES cells, and 
have the ability to create all >200 cell types in the body is still not 
known. Moreover, there appear to be certain cell types that are more 
readily generated from ES cells compared with MAPC, such as for 
instance cardiac myoblasts, whereas it appears for instance more 
easy to generate hepatocyte like cells horn MAPC than ES cells. 
Therefore, I continue to strongly believe that strict comparative 
studies between the two cell populations are needed to determine 
the true potential of the cells, and that the scientific insights gained 
from these studies should be used to determine which of the cells 
will be suitable for use in the clinical setting. 
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