A team of Chinese scientists announced on Tuesday the birth of Retro, a cloned macaque with a new strategy to achieve identical monkeys. The leader of the investigation, Qiang Sun, explains to EL PAÍS that the cloning of human beings would be "completely unacceptable" and assures that it is not in his plans. "We won't even think about it," he says.
The cloning of Dolly the sheep in 1996 sparked a worldwide alert that a laboratory might try to make exact copies of human beings. The technique seemed simple. British embryologist Ian Wilmut's group emptied an egg from a sheep and inserted a nucleus with DNA from an adult cell extracted from the udder of another female. Dolly was a replica of the latter. In 1998, the first cloned calves and mice were obtained. In 1999, goats. In 2000, pigs. In 2002, rabbits. In 2005, dogs. And in 2007, the United Nations University published a report arguing that the cloning of human beings was, perhaps, inevitable.
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Some irresponsible scientists, such as Italian gynecologist Severino Antinori and American biologist Panos Zavos, went so far as to announce the imminent birth of cloned humans more than two decades ago, but the reality was that Doly's technique — called somatic cell nuclear transfer — did not work well with primates, the animal group that includes monkeys and humans. The situation changed in 2018, when Qiang Sun's team announced the birth of the first monkeys cloned with this strategy: two female crab-eating macaques named Zhong Zhong and Hua Hua. The word zhonghua means "Chinese nation." One of the co-authors, Poo Mu-ming, proclaimed in this paper at the time, "There are no barriers to cloning primates, so human cloning is closer to becoming a reality."
The efficiency of the 2018 experiment was extremely low. Qiang Sun and his colleagues created 109 embryos, transferred 79 of them to 21 females, and achieved only six pregnancies. Only the two monkeys were born. In the new study, published Tuesday in the journal Nature Communications, the researchers have improved the technique by adding placental precursor cells. On this occasion they created 113 embryos, transferred 11 to seven females and achieved two pregnancies and a single birth: a male rhesus macaque, which is now three and a half years old. "This new strategy has significantly improved the efficiency of monkey cloning, both in terms of the number of embryos transplanted and the number of pregnant females used," Sun said.
The Chinese researcher explains that they have called the animal Retro, after the acronym for replacement of the trophectoderm, the layer of cells that gives rise to the placenta. "Retro is growing and getting stronger every day. It lives in our animal facility with ample space and sunlight," says the Chinese scientist, director of the non-human primate facility at the Center of Excellence in Brain Sciences and Intelligence Technology in Shanghai.
This new strategy has significantly improved the efficiency of monkey cloning
Qiang Sun, Chinese scientist
German bioengineer Angelika Schnieke, one of the creators of Dolly the sheep, reacted with concern to Qiang Sun's early experiments, which required dozens of pregnant females and mostly resulted in miscarriages and malformed fetuses. "With these cloned primates in China, an ethical barrier has been crossed. We probably have to reconsider what is being done," Schnieke told EL PAÍS in 2018. "Personally, I find it hard to justify cloning monkeys. I am concerned that the cloning of monkeys will continue and spread to other species," he said at the time.
Qiang Sun argues that the use of monkeys is "essential" in the field of biomedical and cognitive research. In 2019, his team used the technique already used with monkeys Zhong Zhong and Hua Hua to create five clones of a crab-eating macaque that had been genetically modified to mimic schizophrenia-like symptoms. Sun argues that these uniform populations of lab monkeys can be very useful for studying genetically-based diseases, such as cancer and many brain disorders. Their new study boasts of "introducing a promising strategy for cloning primates."
Cloning is already routine in other species. In 2010, Argentinian veterinarian Andrés Gambini created the first cloned horses in South America. Currently, he is a researcher at the University of Queensland (Australia) and is scientific director of Ovohorse, a Spanish company based in Marbella that offers services of "cloning dogs, cats, camels and horses, among others".
For Gambini, the birth of Retro is "a remarkable breakthrough" in the field. In his opinion, the fundamental idea of the study – to replace the placenta of cloned embryos with that of embryos generated by in vitro fertilization – is not conceptually new, but its success shows an alternative to improve the efficiency of cloning. The Argentinian veterinarian points out that this approach could also be used to implant embryos of an endangered wild animal into the uteruses of females of similar domestic species. His team already succeeded in 2020 in creating cloned zebra embryos from emptied mare eggs.
Andrés Gambini stresses that the technique is still complex and with low efficiency rates. "Human cloning for reproductive purposes continues to be the subject of intense questioning, not only because the technique is inefficient, leads to embryonic and fetal death, and the physical and mental health of clones is not guaranteed. What is the purpose of generating people through cloning? All the answers involve some legal, ethical or moral dilemma," he says.
The Universal Declaration on the Human Genome and Human Rights prohibits the cloning of people and was adopted by the United Nations in 1998. Dutch jurist Bartha Knoppers, who was involved in drafting it, doesn't think anyone would dare to take the plunge, not even a megalomaniacal dictator. "I think that reproductive human cloning is one of the areas in which there is practically a universal consensus that we should never go down that road," he explained in an interview with EL PAÍS just over a year ago. "It would create an element of industrialization in reproduction and turn people into things that can be copied. It's a red line for me."
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