A monkey was secretly cloned in China and recognized it only 3 years later: are scientists ready to repeat it on humans?
After numerous attempts, scientists have managed to create a healthy rhesus monkey through cloning. The clone was born in China on July 16, 2020, but its existence has only just been reported.
The details of the sensational experiment were reported by NewScientist. Despite the success of the monkey cloning, scientists are still categorical about human cloning.
Falun Lu from the Chinese Academy of Sciences in Beijing said that the monkey, named ReTro, has reached the age of 3 and medical examinations have not yet revealed any health problems.
It is known that she was cloned from fetal cells, not from adult cells. In addition, a non-cloned placenta was used for her development. Therefore, scientists note that cloning is still an extremely difficult task.
Cloning involves creating an individual that is genetically identical to another. Mankind has learned to clone plants very easily, but most animals are much more complicated.
The first mammal to be cloned by scientists from an adult cell was Dolly the sheep. She was born in 1996 and lived for almost 6 years. Subsequently, researchers tried to repeat the success by cloning other mammalian species, but the results were mixed.
Sometimes it works relatively well, but sometimes it's quite the opposite. For example, a team of scientists from South Korea cloned more than 1500 dogs, but the success rate of their experiments was very low: less than 4% of cloned embryos resulted in the birth of live animals. In the case of many other mammalian species, the situation is even worse.
The main problem, as scientists explain, is that developing cells specialize. During this process, various epigenetic markers are added to the DNA of cells, which are responsible for turning certain genes on or off. So when an adult cell is cloned and placed in an empty egg, it already has the wrong epigenetic markers.
In the case of primates, which include monkeys and humans, cloning has proven to be particularly difficult. Although there have been several successful cases, they all came with significant caveats.
For example, in 1999, a rhesus monkey was born, often considered the first primate clone. However, it was created by splitting an embryo, similar to what happens when identical twins are created. This is not the same as cloning an adult cell, as in the case of Dolly the sheep.
In 2022, the birth of a rhesus monkey was also reported, which was cloned from a genetically modified adult, but the clone died shortly after birth.
The most successful attempt so far was the birth of two long-tailed macaques in 2017. Back then, scientists used a special chemical cocktail that helped reboot epigenetic markers. But even in this case, it was about cloning a fetal cell, not an adult.
It was the 2017 scheme that Lu's team tried to apply in their study. However, the only clone born this way did not survive. The researchers concluded that the problem was in the abnormalities in the cloned placentas. Then they transferred a part of the early embryo that develops into a fetus into a non-cloned embryo, from which the internal cell mass was removed.
In this way, the cloned fetus developed inside a non-cloned placenta that is genetically different from it. Theoretically, the resulting fetus could be a mixture of cloned and non-cloned cells, but the team found no evidence of this.
But, as the scientists said, even this complex process allowed cloning only fetal cells, not adult cells. Thus, we can say that no healthy primate has yet been created by cloning adult cells.
So the issue of human cloning remains a distant prospect. And so far away that Lu does not even undertake to predict it.
"The act of human cloning is absolutely unacceptable. We will not think about it," he said.