“This paper really marks the beginning of a new era for biomedical research,” Xiong Zhi-Qi, a researcher studying brain disease at the ION but who was not involved in the work, tells Nature.
These monkeys are not the first primates to be cloned. A rhesus macaque named Tetra was produced in the late 1990s by embryo splitting, the division of an early-stage embryo into two or four separate cells to make clones. Zhong Zhong and Hua Hua, by contrast, were each made by replacing an egg cell nucleus with DNA from a differentiated body cell. The technique—which has previously been employed to clone sheep, cattle, cats, mice, and dogs—can create more clones than embryo splitting and allows researchers greater control over the edits they make to the transferred DNA.
Adapting the approach to monkeys proved difficult, and many attempts by the Chinese team failed: the researchers transferred 79 embryos into surrogate monkeys for just two viable births. “The SCNT procedure is rather delicate,” study coauthor Mu-ming Poo, director of ION, says in a statement. “The faster you do it, the less damage to the egg you have. . . . It is likely that the optimization of transfer procedure greatly helped us to achieve this success.”
Many researchers have been quick to pour water on the idea that the team’s results bring scientists closer to cloning humans. “The work in this paper is not a stepping stone to establishing methods for obtaining live born human clones,” Robin Lovell-Badge of the Francis Crick Institute in London tells reporters (via the The Independent). “This clearly remains a very foolish thing to attempt, it would be far too inefficient, far too unsafe, and it is also pointless.”
But Poo emphasizes that this is not the team’s goal. “There is now no barrier for cloning primate species, thus cloning humans is closer to reality,” Poo tells reporters (via The Guardian). “However, our research purpose is entirely for producing non-human primate models for human diseases; we absolutely have no intention, and society will not permit, this work to be extended to humans.”