Cloned monkey is first to survive in good health after 112 failed attempts

A monkey has been successfully cloned by Chinese scientists and, in a world first, has so far lived for two years.

Researchers have cloned primates before using the same method that created Dolly the Sheep in 1996 but none have ever lived for long, either dying before birth or shortly afterwards.

However, a modified technique designed to create a stronger placenta has seen a rhesus monkey be cloned, be born and live healthily for more than two years, making it the longest-lived primate clone yet. The animal has been labelled “ReTro”.

Only one birth was successful, however, from a total of 113 attempts. 

The process, called somatic cell nuclear transfer (SCNT), involves extracting the genetic information from a standard cell and implanting it into an egg from another monkey that has had its own genetic material removed.

The placing of chromosomes from a body cell into a vacant egg, which acts like a donor, is the same process used to create Dolly the Sheep.

Dogs, cattle, mice and goats are among the other species to be cloned using this process but in primates, it has proven difficult, with a success rate as low as 1 per cent.

Cloning of this kind on primates is prohibited in Europe on ethical grounds, but is conducted legally in China.

A team from the Chinese Academy of Sciences cloned a crab-eating macaque in 2018 but the method has been plagued with problems and a poor survival rate.

The same scientists analysed the development of a normal IVF embryo and compared it to a cloned embryo and found the clones struggled to make a proper placenta and as a result, they rarely attached to the womb of their surrogate mother.

Another step was added to the process to correct this which involved replacing a faulty layer of cells called the trophoblast that surrounds the growing embryo. These cells act as nutrition and are supposed to help the inner cells – which will become the monkey – flourish.

This layer is often the wrong shape and too small in clones, which makes the birth non-viable.

An update to the process saw the scientists grow both a cloned embryo and a normal IVF embryo. The inner cells of both were cut out and the clone was put inside the IVF’s healthier placenta-forming layers.

“Remarkably, using this approach, we successfully achieved the live birth of a healthy [cloned] rhesus monkey that has survived for over two years at the time of preparing this research for publication,” the scientists said in their paper, published in Nature Communications.

They added that the strategy “holds great promise” for improving the dismal success rate of cloning.

The scientists did the work to see if they could create more cloned lab monkeys because their long-term health and survival “is of great importance” because they “are extensively used for basic and clinical research”.

However, the scientists also believe the process of snipping out cells in an early-stage embryo and injecting them into a healthier covering could help people struggling to conceive via IVF.

If people having difficulty conceiving are having issues with IVF because of implantation problems, then this process may be a future possible route to conception, they claimed.

Dr Lluís Montoliu, a researcher at the National Center for Biotechnology in Spain, said this work built on the same team’s cloning attempts on macaques six years ago, and the efficiency of the process remained a large problem that prevented it from being used on people.

The previous study had just 1.5 per cent of embryos leading to live births, with this study being just one out of 113, a less than one per cent success rate.

“The cloning of crab-eating macaques and Rhesus monkeys demonstrate two things,” he said.

“First, it is possible to clone primates. And second, it is extremely difficult to succeed with these experiments, with such low efficiencies, once again ruling out human cloning.

“This poor efficiency confirmed the obvious: not only is human cloning unnecessary and debatable, but if attempted, it would be extraordinarily difficult and ethically unjustifiable.

“Finally, it is worth noting that these experiments could not have been conducted in Europe, as the European Union’s legislation on animal experimentation prohibits the use of non-human primates unless the experiment is aimed at investigating a serious, life-threatening disease affecting humans or the primate species itself, which is not the case in this experiment,” Dr Montoliu added.