A monkey is made from mixing cells of two different individuals. This helps biology but doesn’t have any practical use yet.
■Key points of this article that can be understood in 3 lines
- Chinese scientists made a new monkey by mixing cells. It shows stem cells can help different parts of monkeys.
- The study can help with medicine and environmental conservation. But, it has difficulties like high cost and low efficiency.
- The technique used on mice forty years ago is similar to this one. But it’s unclear whether this method will work for humans. Other gene-editing methods like CRISPR are more direct and have taken over the spotlight.
Achimera is a monster from classical mythology. It has the head of a lion, belly of a goat, and tail of a dragon. In biology, there are chimeras that look similar but we can’t recognize the parts clearly. Scientists design chimera rodents with different cells from different embryos to fight diseases.
A new milestone in chimeras is published in the journal Cell today. The first chimeric monkey was born alive in China. It was generated from embryonic cells of two crab-eating or long-tailed macaques, which are used for research. A team of Chinese researchers, led by Miguel Ángel Esteban, injected stem cells from another embryo into a blastocyst that was five or six days old.
These cells are called stem cells and can contribute to all organs. Scientists injected them into a macaque and allowed it to develop. They used proteins that glow green, sequenced genes, and found that the stem cells ranged from 21% to 92% in different tissues. Six live births resulted from 12 pregnancies. Only one monkey was truly chimeric with the cells throughout its body. The monkey could transfer the genome to its offspring, including the gonads.
Miguel Ángel Esteban, a scientist from China, says that pluripotent stem cells can turn into different body tissues in monkeys. This study proves it. Before, people only knew it happened in mice. But there’s no evidence for humans because it’s not ethical to test.
New keys to embryonic stem cells
Así has been working for 15 years in China on a similar line of work. She reprogrammed cells to form any organ or tissue, making them pluripotent again. Her lab developed kidneys with up to 50% human cells by introducing them into pig embryos. This could lead to growing organs in animals for transplants. Another Spaniard, Juan Carlos Izpisúa, started developing pig embryos with a small percentage of human cells six years ago.
A researcher in bioengineering systems at the Pompeu Fabra University of Barcelona, Alfonso Martínez Arias, says that this work is important for the developmental biology of mammals. He thinks that we can learn a lot from it because not all embryonic stem cells are the same. They vary depending on how they were grown and isolated which is unexpected according to experts.
Chinese researcher Zhen Liu, from the Chinese Academy of Sciences, conducted a study with practical uses. It can help create better models for studying illnesses in monkeys and other biomedical research. This helps species conservation as well as genetic engineering.
Decades to go from mice to monkeys
“Biologically, this achievement is a big deal. It’s important because we’re primates too,” says Lluis Montoliu, a genetics expert. However, mice were chimeric almost 40 years ago. This work is complex and alternative treatments are available. Nevertheless, the chimeric monkey provides new data for researchers. But in 1984, Allan Bradley showed that it was possible to create chimeric mice that passed on the genome of injected cells to their offspring.”
In 1989, scientists conducted an experiment that led to the birth of the first mutant mouse. This technique has since allowed laboratories around the world to generate thousands of genetically modified mice. These mice have inactivated genes, allowing researchers to understand their function compared to normal mice. This breakthrough has advanced research on many diseases, leading to the Nobel Prize in Medicine for its creators in 2007.
The article published in Cell is a great step in biomedical research. Mice were the closest model to humans, but now we have a closer species. However, doubts exist about its usefulness for medicine application.
Why it has a difficult real application
This research can create chimeric monkeys with mutations like mice. Genetically modified macaques help study human diseases. However, it may not be useful in practice. The technique has existed since 2013 using CRISPR tools. This allows inactivating genes directly without pluripotent cells. Montoliu says it is 10 years late.
The CRISPR technique is like scissors that cut and paste the genome. It makes animals with the chosen gene mutation. Macaques had it done in 2014. There’s an easier way to get the same results as chimeric monkeys.
According to Martínez Arias, the experiment paves the way for non-human primates to be used as models for human biology. This can help in studying the effects of genetic modifications and disease models. He also acknowledges that these experiments are not easy because they are expensive and need special maintenance. Additionally, the gestation period is long, and there is only one baby per mother which makes it even more challenging.
The Cell article displays the complexity of the new alternative. More than 200 original embryos were used, and one chimeric monkey was produced with low efficiency. The CNB expert comments that this is “extremely poor efficiency.” Practical application in labs is “unthinkable” due to these conditions. Dozens of female macaques were also impregnated.
Under these conditions, it is not ethical, scientific or technically acceptable to consider applying this advance in humans. We know how to do it but its significance may be limited. A monkey that is a chimera is a milestone for science and culture, but not so much for medicine at the moment.
- Cell, Cao et al. “Live Birth of Chimeric Monkey with High Contribution from Embryonic Stem Cells” https://cell.com/cell/fulltext/S0092-8674(23)01087-5