For the first time, a cloned rhesus monkey (Macaca mulatta) has lived into adulthood—surviving for more than two years so far.
The feat, described today in Nature Communications, marks the first successful cloning of the species. It was achieved using a slightly different approach from the conventional technique that was used to clone Dolly the sheep and other mammals, including long-tailed macaques (Macaca fascicularis), the first primates to be cloned.
By replacing the placenta of the cloned embryo with that of embryos produced by an in vitro fertilization technique, scientists reduced developmental defects that can hinder embryo survival while using fewer embryos and surrogate mothers. The new technique could unlock possibilities for using cloned primates in drug testing and behavioral research.
…Success in primates has been particularly limited. When researchers cloned long-tailed macaques in 2018, they created 109 cloned embryos and implanted nearly 3⁄4ths of them into 21 surrogate monkeys, resulting in 6 pregnancies. Just two of the monkeys survived birth. In 2022, researchers cloned a rhesus monkey using SCNT, but the animal survived for less than 12 hours2.
…To address this, the researchers developed a technique that involved replacing the SCNT trophoblast—the outer layer of cells in a developing embryo, which later forms the major part of the placenta—with trophoblasts from ICSI embryos. This meant the embryos developed a “natural placenta”, says study co-author Zhen Liu, a neuroscientist at the Chinese Academy of Sciences, “but the fetus is still a cloned fetus”.
…One healthy clone Using this approach, the researchers created 113 cloned rhesus monkey embryos and implanted 11 of them into 7 surrogates, resulting in two pregnancies.
One of the pregnant surrogates gave birth to a healthy male rhesus monkey named ReTro, which has survived for more than two years. (The other surrogate carried twins, which died on day 106 of gestation.)