New species of cloned monkey highlights the limits of cloning

(CNN) — Meet Retro, a cloned rhesus monkey born on July 16, 2020.

He is now more than 3 years old and “doing well and growing strong,” according to Falong Lu, one of the study's authors. Stady Published Tuesday in the journal Nature Communications describes how Retro technology came to be.

Retro is the second species of primate that scientists have successfully cloned. The same team of researchers announced in 2018 that they had cloned two identical cynomolgus monkeys, which are still alive today.

The cloned rhesus monkey was named Retro and is in good health, according to the research team. Image source: Zhaodi Liao et al., Nature Communications

“We have achieved the first live and healthy cloned rhesus monkey, an achievement that turns the impossible into possible, although the efficiency is very low compared to natural fertilized embryos,” said Lu, a researcher at the Key Laboratory for Molecular Analysis. Developmental Biology and the Institute of Genetics and Developmental Biology of the Chinese Academy of Sciences. “At the moment, we have not yet had a second live birth.”

The first cloned mammal (Dolly the Sheep) was created in 1996 using a technique called somatic cell nuclear transfer, or SNCT, where scientists essentially reconstruct an unfertilized egg by fusing the nucleus of a somatic cell (not from the sperm or egg) with the egg. from which the nucleus has been removed.

Since then, scientists have cloned many species of mammals, including pigs, cows, horses and dogs, but the process has been hit or miss, with only a small percentage of embryos transferred to surrogate mothers giving birth to viable offspring.

“In a way, we have made a lot of progress, in the sense that after Dolly, many species of mammals have been cloned, but the truth is that inefficiency is still a big obstacle,” says Miguel Esteban, lead researcher at the Institute of Science and Technology. Biomedicine and Health Guangzhou from the Chinese Academy of Sciences. He was not involved in the latest research, but he has collaborated with some members of the research team on other primate studies.

Rhesus monkey clone

The Chinese team, based in Shanghai and Beijing, used a modified version of TNCS in their work with cynomolgus monkeys (Macaca fascicle(And he mastered the technique of cloning the rhesus monkey)Mulatto Macaca).

During hundreds of failed cloning attempts, they realized that in the first cloned embryos, the outer membrane that forms the placenta had not developed properly. To solve this problem, they performed a procedure called megaendogenous cell transplantation, which consists of inserting cloned endogenous cells into a non-cloned embryo, which allowed the cloned embryo to develop normally, Esteban explained.

The team then tested the new technique on 113 reconstructed embryos, 11 of which were transferred to seven surrogate wombs, resulting in one live birth, according to the study.

“We believe there may be additional abnormalities…that need to be corrected. Strategies to improve the success rate of TNCS in primates remain our main focus in the future,” Lu said.

The first two cloned monkeys, Zhong Zhong and Hua Hua, are now more than 6 years old and living “happy and healthy lives” with others of their kind. According to Lu, researchers have not yet determined any possible limits to the lifespan of the cloned monkeys.

Zhong Zhong and Hua Hua are often described as the first cloned monkeys. but, In 1999 It was cloned Small Indian monkey Using what researchers consider a simpler cloning method. In this case, the scientists split the embryos, as happens naturally when identical twins develop, rather than using an adult cell as is the case with TNCS technology.

Implications of cloning monkeys

Cloning monkeys could speed up biomedical research, researchers say, as there are limits to what scientists can learn from laboratory mice. Research on non-human primates, which are more similar to humans, has been key to life-saving medical advances, such as creating vaccines against Covid-19, according to new research. a report From a collection of the National Academies of Sciences, Engineering, and Medicine published in May.

The use of monkeys in scientific research is a controversial topic due to ethical concerns about animal welfare. The team claimed to have followed Chinese laws and guidelines governing the use of non-human primates in scientific research.

The UK's Royal Society for the Prevention of Cruelty to Animals said it had “serious ethical and welfare concerns about applying cloning technology to animals. Cloning animals requires procedures that can cause pain and distress, and there may be significant failure and mortality.”

Esteban said the ability to produce genetically identical monkeys could be beneficial.

“This research is proof of the principle that cloning can be done in different species of non-human primates, and opens the door to new ways to increase efficacy. Cloned monkeys can be genetically modified in complex ways that wild monkeys cannot do; this has many advantages,” he added: “Implications for disease modeling. There is also a species conservation perspective.”

Dr. Luis Montolio, a research scientist at Spain's National Biotechnology Center (CNB-CSIC) who was not involved in the research, said cloning both types of monkeys showed two things.

“First of all, it is possible to clone primates,” he said in a statement. “Secondly, which is no less important, it is extremely difficult to succeed in these experiments, with such low efficiency.”

He added that the low success rate of this process demonstrated that “human cloning was not only unnecessary and controversial, but that, if attempted, it would be extremely difficult and morally unjustified.”

“Cloning humans for reproductive purposes is absolutely unacceptable,” Lu said.