Cloning Challenges: The Journey of Retro, the Second Successfully Cloned Primate

In a groundbreaking study published in the journal Nature Communications, scientists revealed the successful cloning of Retro, a rhesus monkey born on July 16, 2020. This achievement marks a significant stride in primate cloning, as Retro becomes only the second cloned primate species, following the earlier cloning of cynomolgus monkeys in 2018 by the same research team.

Falong Lu, a lead researcher at the Chinese Academy of Sciences, expressed the significance of this milestone, stating, “We have achieved the first live and healthy cloned rhesus monkey, which is a big step forward that has turned impossible to possible, although the efficiency is very low compared to normal fertilized embryos.”

The technique employed by the Chinese research team involved a modified version of somatic cell nuclear transfer (SCNT), a method used since the creation of the first cloned mammal, Dolly the sheep, in 1996. Facing challenges during the cloning attempts, the researchers discovered that the outer membrane forming the placenta did not develop properly in early cloned embryos. To address this, they utilized inner cell mass transplantation, allowing the clone to develop normally.

Despite this success, the overall efficiency of the process remains low, with only one live birth out of 113 reconstructed embryos. The researchers acknowledge the need for further refinement to enhance the success rate of SCNT in primates.

Cloning has seen success in various mammalian species, but primates present unique challenges. Miguel Esteban of the Guangzhou Institute of Biomedicine and Health emphasized the importance of the research, stating, “This research is proof of principle that cloning can be done in different non-human primate species and opens the door to new ways of enhancing the efficiency.”

The cloned monkeys, Zhong Zhong and Hua Hua, born in 2018, are now over 6 years old, living healthy lives. The implications of cloning primates extend to biomedical research, offering opportunities for genetic engineering and disease modeling. However, ethical concerns surrounding animal welfare persist, and critics caution against the application of cloning technology to animals. Dr. Lluís Montoliu, a research scientist at the National Center for Biotechnology in Spain, highlighted the difficulties and ethical considerations surrounding primate cloning, asserting that the low success rate emphasizes the impracticality and ethical unjustifiability of reproductive cloning in humans. Lu echoed these sentiments, emphasizing the unacceptable nature of reproductive cloning in humans.