398 
Monitoring Stem Cell Research 
or genetic ablation allowed the ntES cells to efficiently populate the 
myeloid and to a lesser degree the lymphoid lineages of these mice. 
Functional B and T cells that had undergone proper rearrangements 
of their immunoglobulin and T cell receptor alleles as well as serum 
immunoglobulins were detected in the transplanted mutants. 
Hence, important cellular components of the immune system were 
restored in mice that previously were unable to produce these cells. 
This experiment demonstrated that embryonic stem (ES) cells 
derived by NT from somatic cells of a genetically afflicted individual 
can be combined with gene therapy to treat the underlying genetic 
disorder. Because Rag2 deficiency causes an increase in NK activity 
and necessitated the elimination of NK cells prior to transplantation 
in the above-described experiments, some have concluded that "The 
experiment failed to show success with therapeutic cloning” 
(Coalition and Ethics, 2003) and that "This indicates that the only 
successful therapy using cloned embryos would be through 
'reproductive' cloning, to produce bom clones who can serve as 
tissue donors for patients" (Prentice, 2002). This is a troubling 
misinterpretation of the data, (i) It has been shown that ES cell- 
derived hematopoietic cells can successfully engraft and rescue 
lethally irradiated mice indicating that increased NK activity is a 
peculiarity of Rag2-deficiency (Kyba et al., 2002). Therefore, it would 
seem that for most diseases, no anti-NK treatment would be required 
to assure engraftment of ES cell-derived somatic cells, (ii) It is correct 
that treatment of a human patient v\hth Omenn syndrome, which is 
equivalent to Rag2 deficiency, by SCNT may also require anti-NK 
treatment to transiently reduce NK activity. This would allow the 
transplanted cells to engraft as in the mouse experiment. Once these 
cells are successfully engrafted, there is every reason to believe that 
such anti-NK treatment would no longer be necessary. 
In conclusion, the mouse experiment indicates that, unlike the 
situation with reproductive cloning, no biological barriers exist that 
in principle prevent the use of SCNT to treat human diseases. The 
technical issues in using SCNT and human stem cells for therapeutic 
purposes need, however, to be solved, but there are no indications at 
present that these represent formidable problems that will resist 
relatively rapid solution. 
vn. Faulty reprogramming after nuclear transfer: does it interfere 
with the therapeutic potential of ES cells derived by SCNT? 
PRE -PUBLICATION VERSION 
