A cloned rhesus monkey has reached adulthood for the first time ever, with the unique primate now more than 3 years old, according to Chinese researchers.
Retro — who was born on July 16, 2020 — was the sole birth of 113 cloned embryos created by scientists at the State Key Laboratory of Molecular Developmental Biology and Institute of Genetics and Developmental Biology at the Chinese Academy of Sciences.
His birth and development now mark a major milestone for cloning research as outlined in the paper published on Nature Communications on Tuesday.
“We have achieved the first live and healthy cloned rhesus monkey, which is a big step forward that has turned impossible to possible,” researcher Falong Lu told CNN.
Retro was born using a slightly different technique from the ones that birthed Dolly the sheep, the first animal cloned by scientists in 1996 that became the standard model.
The researchers at the Chinese Academy of Sciences replaced the placenta of the cloned embryo with embryos produced by in vitro fertilization, a new technique to reduce the defects that hurt the survival rate when using embryos and surrogate mothers.
With the new approach, the researchers created 113 cloned rhesus monkey embryos and were able to implant 11 of them into seven surrogates.
The experiment resulted in two pregnancies, with Retro being the sole birth after the other surrogate carried twins that died 106 days into gestation.
Clones tend to have extremely low birth and survival rates, as previous experiments have also resulted in just one or two births.
Last year, a cloned rhesus monkey using traditional cloning methods survived for less than 12 hours, according to a paper published in Science Advances.
Given Retro’s age and health, the Chinese researcher’s work could set a precedent for future cloning of rhesus monkeys, the second species of primates that have been successfully duplicated.
The same Chinese team was responsible for the birth of two identical cloned cynomolgus monkeys that are still alive today and at more than 6 years old.
“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,” Miguel Esteban, principal investigator with the Guangzhou Institute of Biomedicine and Health at the Chinese Academy of Sciences told CNN.
“Cloned monkeys can be genetically engineered in complex ways that wild-type monkeys cannot; this has many implications for disease modeling,” he added.
The research, however, is not without its detractors as animal rights advocates and officials have scrutinized the impacts of the procedure and testing on the primates.
“Cloning animals requires procedures that can cause pain and distress, and there can be high failure and mortality rates,” the UK’s Royal Society for Prevention of Cruelty to Animals said in a statement.