A team of Chinese scientists has achieved a breakthrough in primate cloning, successfully cloning a two-year-old rhesus macaque named Retro. This accomplishment marks a significant advancement in the field, refining the technique that initially gave rise to Dolly the sheep in 1996, as revealed in a study published on Tuesday.
Cloning primates, particularly macaques, poses immense challenges, and scientists faced years of failure before achieving success. The researchers, from the Institute of Neuroscience at the Chinese Academy of Sciences in Shanghai, employed a technique using the placenta, aiming to create genetically identical rhesus macaques for medical research.
Since the cloning of Dolly, over twenty mammalian species, including dogs, cats, pigs, and cattle, have been cloned using Somatic Cell Nuclear Transfer (SCNT). However, it took two decades for scientists to successfully clone the first primate. Genetically identical crab-eating macaques, named Hua Hua and Zhong Zhong, were born in 2018 using the SCNT method.
While this scientific achievement is noteworthy, the success rate remains low, with less than 2% of crab-eating macaques born alive. Previous attempts to clone Rhesus macaques, a species that gave its name to the blood group system, had all ended in failure.
The Chinese research team identified the primary reason for these failures—abnormalities in the placentas supplying nutrients to cloned embryos. To address this, they replaced the cells of the future placenta, known as trophoblasts, with those from a healthy, non-cloned embryo. This modification significantly improved the success rate of SCNT cloning, leading to the birth of Retro, a cloned rhesus macaque who is now two years old.
Despite the achievement, the success rate remains below 1%, with only one out of 113 embryos surviving. While this breakthrough opens possibilities for studying diseases and testing medications with genetically identical primates, the ethical considerations and low success rates underscore the challenges and limitations of primate cloning. Scientists, including Qiang Sun, the lead author of the study, express reservations about the cloning of humans, deeming it “unacceptable” under any circumstances.