Scientists Have a Cloning Breakthrough

3-year-old Retro is the world's first rhesus monkey cloned using somatic cell nuclear transfer
By Arden Dier,  Newser Staff
Posted Jan 17, 2024 7:44 AM CST
This Little Guy Marks a Cloning Breakthrough
ReTro, a cloned rhesus monkey, photographed 17 months after his July 2020 birth.   (Zhaodi Liao et al., Nature Communications)

His name is Retro, he's 3 years old, and he's the world's first rhesus monkey cloned using somatic cell nuclear transfer, or SCNT. Chinese researchers announced the July 2020 birth on Tuesday, noting "the first live and healthy cloned rhesus monkey" marked "a big step forward that has turned impossible to possible" and could help accelerate biomedical research. Retro was created using a version of the same method used to clone the first mammal, Dolly the sheep, in 1996. "Scientists essentially reconstruct an unfertilized egg by fusing a somatic cell nucleus (not from a sperm or egg) with an egg in which the nucleus has been removed," per CNN. The embryo, transferred into a surrogate, "grows into the same creature that donated the replacement nucleus," per AFP.

The rhesus monkey is only the second species of primate cloned through SCNT. The research team used a version of the technique to create two identical cloned cynomolgus monkeys, a type of macaque, in 2018. Zhong Zhong and Hua Hua are now 6 years old and living a "happy and healthy life" with other members of their species, researchers said, per CNN. Rhesus monkeys are preferred in medical testing "because of their genetic similarity to humans," per the BBC. A rhesus monkey named Tetra was cloned in 1999 using a simpler method called embryo splitting. But SCNT can create far more clones at once. The successful SCNT cloning of Retro came after years of failures. One previous attempt resulted in a live birth, but the monkey died less than 24 hours later, as described in Nature Communications, per AFP.

Researchers discovered abnormalities in the cloned cells that would become the placenta. Success came after replacing the cloned cells with cells from a healthy, non-cloned embryo, per AFP. Still, the success rate was less than 1%, with one of 113 embryos surviving. Retro resulted from one of 11 embryos transferred to surrogates. He's "doing well and growing strong," study co-author Falong Lu says, per CNN, noting there may be other "abnormalities to be fixed" as researchers aim to create identical monkeys to study diseases. "Genetically identical animals give like-for-like results, providing greater certainty in trials," per the BBC, though there are ethical concerns. "Cloning animals requires procedures that can cause pain and distress, and there can be high failure and mortality rates," says the Royal Society for Prevention of Cruelty to Animals. (More cloning stories.)

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