Scientists in China who created the world's first cloned monkeys have promised they do not plan to repeat the technique with humans.
The birth of two identical long-tailed macaques – named Zhong Zhong and Hua Hua – marked the first time primates had been cloned using the same technique that created Dolly the sheep.
While the achievement was seen as a breakthrough, critics raised ethical concerns about the research and suggested it could lead to a “slippery slope” that would ultimately result in human cloning.
However, the Chinese scientists who carried out the research said their interest in cloning primates came from a strictly medical perspective.
“We have no plan to clone humans, and social ethics would by no means allow that practice,” Dr Mu-ming Poo, co-author of the macaque study, told Chinese state news outlet Xinhua.
Instead the researchers said their study, published in the journal Cell, provided a framework for understanding human diseases.
Dr Poo acknowledged that while their work could theoretically lead to cloning humans, they were only interested in advancing the treatment of brain conditions such as Alzheimer’s disease and autism.
The scientists have previously emphasised the “very strict ethical standards” required for performing cloning research on primates.
“Just like nuclear power and artificial intelligence, cloning technology is also a double-edged sword,” said Dr Qiang Sun, the director of the Suzhou Nonhuman Primate Research Facility and leader of the study.
By creating cloned monkeys, researchers could potentially undertake experiments in which all the subjects are genetically identical apart from the genes they want to manipulate and study.
“This will generate real models not just for genetically based brain diseases, but also cancer, immune or metabolic disorders, and allow us to test the efficacy of the drugs for these conditions before clinical use,” said Dr Sun.
Professor Darren Griffiths, a geneticist at the University of Kent who was not involved in the study, confirmed there were clear benefits to this research.
“A primate model that can be generated with a known and uniform genetic background would undoubtedly be very useful in the study, understanding and ultimately treatment, of human diseases, especially those with a genetic element,” he said.
However, he also noted the controversy that inevitably surrounds findings of this nature.
“The first report of cloning of a non-human primate will undoubtedly raise a series of ethical concerns, with critics evoking the slippery slope argument of this being one step closer to human cloning,” he said.
Other scientists noted the medical advantages of performing this kind of research on animals that are so evolutionarily close to humans, but stated human cloning remains a bad idea.
“This clearly remains a very foolish thing to attempt,” said Dr Robin Lovell-Badge from the stem cell biology and developmental genetics laboratory at the Francis Crick Institute.
“It would be far too inefficient, far too unsafe, and it is also pointless. Clones may be genetically identical, but we are far from only being a product of our genes.”
Besides the research leading to human clones, observers have pointed to other ethical issues surrounding the cloned monkeys, such as the health issues that have been associated with cloned animals in the past.
The somatic cell nuclear transfer technique the scientists used to produce the clones was described by Dr Poo as “rather delicate”, and required 79 cloned embryos to be used in order to obtain two healthy monkeys.
The researchers also produced two other newborn monkeys, but neither survived for long.
However, Dr Sun and his colleagues said cloning macaques could have the benefit of reducing the number of monkeys used for animal testing in labs, and that the technique could even be used to preserve endangered primates such as golden monkeys.
Dr Sun also called for regulations to ban the inappropriate use of cloning technology.
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