Meet The World’s First Cloned Rhesus Monkey To Reach Adulthood

world's first cloned monkey
In world's first, a cloned rhesus monkey named ReTro survived to adulthood. | Credit: Zhaodi Liao et al., Nature Communications

Chinese Academy of Sciences: Scientists have achieved a significant milestone in the field of animal cloning. For the first time, a cloned rhesus monkey (Macaca mulatta) has survived into adulthood. At over two years old, the cloned monkey named ReTro represents a breakthrough in primate cloning that could unlock new possibilities for medical research using cloned non-human primates.


ReTro was cloned via somatic cell nuclear transfer (SCNT), the same technique used to create Dolly the sheep in 1996. However, researchers from the Chinese Academy of Sciences in Shanghai made key modifications to improve embryo and fetal survival rates. In a standard SCNT procedure, cloned embryos are implanted into surrogate mothers for gestation. However, primate cloning via SCNT has faced enormous challenges due to high rates of miscarriage, stillbirth, and neonatal death.



Dolly The Sheep | Credit: Britannica


To address these issues, the Chinese researchers took a different approach. They collected fertilized eggs from rhesus monkey embryos created via in vitro fertilization (IVF) and surgically transferred the placentas and fetal membranes of these IVF embryos into surrogate mothers. They then inserted the somatic cell nuclei from donor animals into enucleated eggs and implanted these cloned embryos in the uteruses containing the IVF-derived placentas and membranes.


Essentially, the researchers “piggybacked” the cloned embryos onto the placental structures of naturally conceived embryos to boost fetal development. This novel technique, known as placenta-assisted cloning, significantly improved embryo survival rates compared to conventional SCNT. Of the 127 cloned embryos created, scientists were able to implant 35 into surrogate mothers – a much higher rate than previous primate cloning attempts.



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The breakthrough was a success – five pregnancies were achieved, resulting in the live birth of ReTro on January 18, 2018. Remarkably, the monkey survived the critical neonatal period and has grown into a healthy juvenile monkey surviving well beyond two years of age – a first for a cloned primate. Their long-term survival proves that placenta-assisted cloning can effectively overcome placental defects that often cause cloned primate embryos to die in utero or shortly after birth.


The achievement has massive implications. Rhesus monkeys are physiologically very similar to humans and are widely used in biomedical research. However, individual monkeys can vary significantly in their genetic makeup and responses to experimental treatments. Cloned monkeys could offer genetically identical subjects for research – allowing scientists to better control for genetic variability and obtain more consistent, reproducible results from studies in areas like drug testing, toxicology, transplantation, and regenerative medicine.


Cloned primates could also help address the global shortage of monkeys for research. Breeding programs take over a decade to increase monkey numbers, but cloning techniques could rapidly multiply the numbers of purpose-bred research monkeys with well-characterized genomes. Some experts estimate that cloned monkeys could replace over 100,000 purpose-bred monkeys annually. This would significantly reduce costs for research while avoiding many of the animal welfare issues associated with wild-caught monkeys or large breeding colonies.



The Complexities


Of course, primate cloning remains a complex procedure with many technical challenges. The Shanghai team’s success rate of 5% per transferred embryo was still quite low compared to normal IVF success rates. However, their placenta-assisted cloning approach has overcome key hurdles preventing cloned primates from surviving to term. With further refinement, the technique could allow for scaled-up production of cloned non-human primates for the first time.


ReTro’s continued survival proves that primate cloning is possible and that cloned monkeys can live long healthy lives. Their landmark achievement has taken the field of animal biotechnology a giant step closer to realizing the promise of cloned primates for accelerating medical research and progress. 


With additional study and technical improvements, placenta-assisted cloning may finally deliver on the long-held dream of generating genetically uniform non-human primates on demand. The world’s first cloned monkey is a true pioneer who has rewritten history books and set the stage for a new era in biomedical science.


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