Two monkeys are making headlines around the world. Now barely two months old, they might help lead the way down the path to some of the Holy Grails of biomedical research — at least that’s the hope of their creators.
Zhong Zhong and Hua Hua, the identical long-tailed macaques, were created at the Chinese Academy of Sciences Institute of Neuroscience in Shanghai with the same method that gave birth to Dolly the sheep in 1996. Known as somatic cell nuclear transfer, or SCNT, it takes the nucleus of a differentiated cell from one animal and infuses it into an empty egg cell from another. An electric current triggers the egg to develop into an early embryo, and the resulting fetus, grown in a surrogate, would be a replica of the animal that donated the nucleus.
Scientists have cloned more than 20 species this way, but cloning primates remained a unique challenge. Previous attempts have never progressed beyond the early embryo stage.
The breakthrough here was the introduction of two modulators — specifically, Kdm4d mRNA and a histone deacetylase inhibitor called trichostatin A — in the one-cell stage that switched on or off a number of genes that were affecting embryo development.
From there, the researchers yielded what they hope to be the first of many genetically uniform monkey models that, combined with gene editing tools, could shed light on disease mechanisms and offer therapeutic testing ground for diseases that have eluded human understanding, such as Alzheimer’s and Parkinson’s. Those are areas where mice models have proven woefully inadequate in terms of predicting human reactions to drugs; multiple other genetic diseases could also be targets.
But — as one would reasonably expect — this cloning success carries important caveats. First off, it basically only works in fetal cells. While two babies were born using adult monkey cumulus, they were both short-lived and one had abnormal body development.
Furthermore, the low success rate means producing a population of cloned monkeys large enough to be effective would require an exponentially larger number of embryos and surrogates. At that scale, the practical and ethical questions already surrounding primate research would likely snowball into something even bigger.
To put things into perspective, Zhong Zhong and Hua Hua were the only lucky ones from six pregnancies from 21 surrogates with 79 implanted embryos between them. An additional 22 pregnancies were confirmed among 42 surrogates in the adult cell group.
So no, cloned monkeys are not coming to a lab near you anytime soon. But it’s sure to set off — and it already has — a flurry of debate and, possibly, new research.
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