Several weeks ago, the Institute of Neuroscience in Shanghai made, what many people have described as, controversial progress when two macaque monkey clones were created successfully using Somatic Cell Nuclear Transfer (SCNT). Named Zhong Zhong and Hua Hua, these monkeys were produced using the same technique that was used to produce Dolly the sheep in 1996. This method, SCNT, involves the transfer of a DNA-containing nucleus of a somatic (body) cell, which has two complete sets of chromosomes, into an egg cell that has had its nucleus removed.
The cloning of mammals has been done many times before, however, never to a mammal so closely related to the human race. It has taken many years for scientists to successfully clone a complex, non-human primate, yet success in doing so has made the cloning of humans appear more feasible than it once was. However, do not expect to see a copy of yourself as you walk out to your car after work. The researchers who conducted this study stated that the purpose of cloning non-human primates is unrelated to human reproductive cloning. Instead, it was to allow the production of genetically uniform monkeys for studying human disease mechanisms and therapeutic treatments for Alzheimers research.
How it works is that, during natural fertilization, the egg cell nucleus only has one complete set of chromosomes until it has combined with a sperm cell, an event that provides a second set of chromosomes and initiates cell division. When a nucleus from a body cell containing both sets of chromosomes is transferred into the enucleated egg cell, factors in the cytoplasm of the egg cell alter the DNA expression of the implanted nucleus. This process of reprogramming enables the nucleus to behave like the nucleus of a fertilized egg. However, in this study the process was only successful when the nucleus came from a fetal fibroblast. When adult cell nuclei were used, the clones were unable to survive due to developmental and respiratory complications. The authors of the experimental research paper, published in Cell Journal, suspect that this is because adult nuclei are more difficult to reprogram than fetal nuclei.
Once the body cell nucleus is implanted into the egg cell, a shock is administered and the egg cell begins division as if it had just combined with a sperm cell. These dividing cells can then be implanted into a surrogate mother’s uterus to produce a clone. The stem cells can also be used therapeutically to replace diseased tissue.
A common concern is that, intentional or not, Zhong Zhong and Hua Hua have provided us with knowledge bringing us a little closer to cloning humans. While I agree that this technological progress definitely deserves our moral consideration, human reproductive cloning is still far from becoming a reality. The massive inefficiency of the method (only 2 out of 79 embryos survived) in addition to the numerous ethical dilemmas that accompany it are enough to prevent human reproductive cloning for a very long time.