396 
Monitoring Stem Cell Research 
represent a major stumbling block to efforts aimed at making nuclear 
cloning a safe reproductive procedure for the foreseeable future. 
It has been argued that the problems in mammalian cloning are 
similar to those encountered with IVF 30 years ago: Thus, following 
this argument, the methods of culture and embryo manipulations just 
would need to be improved to develop reproductive cloning into a 
safe reproductive technology that is as acceptable as IVF. This 
argument appears to be fundamentally flawed. It is certainly correct 
that merely “technical" problems needed to be solved to make IVF 
efficient and safe. It is important to distinguish between the 
perfection of technical skills to imitate a biological event and the 
development of wholly new science to overcome the blocks to events 
that have severe biological restrictions. Nuclear cloning faces serious 
biological barriers that cannot be addressed by mere adjustments in 
experimental technique. Indeed, since the birth of Dolly no progress 
has been made in solving any of the underlying biological issues of 
faulty gene reprogramming and resulting defective development. 
VI. Therapeutic applications of SCNT 
(i) Reproductive cloning vs. therapeutic cloning 
In spite of the biological and ethical barriers associated with 
reproductive cloning, nuclear transfer technology has significant 
therapeutic potential that is within our grasp. There is an enormous 
distinction between the goals and the end product of these two 
technologies. The purpose of reproductive cloning is to generate a 
cloned embryo that is then implanted in the uterus of a female to 
give rise to a cloned individual. In contrast, the purpose of nuclear 
transplantation therapy is to generate an embryonic stem cell hne 
that is derived from a patient (referred to as “ntES cells") and can be 
used subsequently for tissue replacement. 
Many scientists recognize the potential of NtES cells for organ 
transplantation (for recent review see (Hochedlinger and Jaenisch, 
2003). This procedure is currently complicated by immune rejection 
due to immunological incompatibility. Thus, virtually all organ 
transplants undertaken at present involve the use of donor organs 
that are recognized as foreign by the immune systems of the 
recipient and thus are targeted for destruction by these immune 
systems. To treat this “host versus graft" disease, 
immunosuppressive drugs are routinely given to transplant 
PRE -PUBLICATION VERSION 
