Monkey embryos containing human cells were manufactured in a laboratory, a study confirmed that spurred new debate on the ethics of such experiments.
The embryos are known as chimeras, organisms whose cells are derived from two or more “individuals”, and in this case different species: a long-tailed macaque and a human.
In recent years, researchers have produced pig embryos and sheep embryos that contain human cells. According to them, this is important because one day it will be possible to grow human organs in other animals, which will increase the number of organs available for transplantation.
Now, scientists have confirmed that they produce macaque embryos that contain human cells, revealing that the cells can survive and even multiply.
In addition, the researchers, led by Prof Juan Carlos Izpisua Belmonte of the Salk Institute in the USA, said that the results provide new insight into communication pathways between cells of different species: work that can help them in their efforts to make chimeras with species that are less closely related to our own.
“These results may help to better understand early human evolution and primate evolution and develop effective strategies to improve human chimerism in evolutionarily distant species,” the authors wrote.
The study confirms rumors reported in 2019 in the Spanish newspaper El País that a team of researchers led by Belmonte produced monkey-human chimeras. The word chimera comes from an animal in Greek mythology that is said to be part lion, part goat and part snake.
The study, published in the journal Cell, reveals how the scientists took specific human fetal cells called fibroblasts and reprogrammed them to become stem cells. These were introduced into 132 embryos of long-tailed macaques six days after fertilization.
“Twenty-five human cells were injected and on average we observed about 4% of the human cells in the monkey epiblast,” said Dr. Jun Wu, a co-author of the research now at the University of Texas’ southwestern medical center was observed, said.
The embryos were allowed in petri dishes and terminated 19 days after the stem cells were injected. To see if the embryos contained human cells, the team designed the human stem cells to produce a fluorescent protein.
The results show, among other things, that all 132 embryos contain human cells on day seven after fertilization, although the part containing human cells has decreased over time.
“We have shown that human stem cells have survived and generated additional cells, as usually develop as primate embryos and form the low cells that eventually lead to all the organs of an animal,” Belmonte said.
The team also reported that they found some differences in cell interactions between human and monkey cells within chimeric embryos, compared to embryos from apes without human cells.
Wu said they hoped the research would help “help transplant human tissues and organs into pigs to overcome the shortage of donor organs worldwide”.
Prof Robin Lovell-Badge, a developmental biologist at the Francis Crick Institute in London, said at the time of El País’ report that he was not concerned about the ethics of the experiment, noting that the team only had a ball of cells. manufactured. But he noted that problems could arise in the future if the embryos are allowed to develop further.
Although this was not the first attempt to make chimeras from apes – another group reported such experiments last year – the new study has rekindled such concerns. Prof Julian Savulescu, director of the Oxford Uehiro Center for Practical Ethics and co-director of the Wellcome Center for Ethics and Humanities at the University of Oxford, said the research opened up a Pandora’s subject for human-non-human chimeras.
“These embryos were destroyed at 20 days of development, but it is only a matter of time before human-non-human chimeras are successfully developed, perhaps as a source of organs for humans,” he said, adding that a important ethical question about the moral go. status of such creatures.
‘Before experiments on live-born chimeras or their organs are extracted, it is essential that their mental abilities and lives are properly assessed. “What looks like a non-human animal can be spiritually close to a human being,” he said. “We need new ways to understand animals, their mental life and relationships before they are used for human benefit.”
Others expressed concern about the quality of the study. Dr Alfonso Martinez Arias, an associate professor at the Department of Genetics at the University of Cambridge, said: ‘I do not think the conclusions are backed up by solid data. The results, as far as can be interpreted, show that these chimeras do not work and that all experimental animals are very sick.
“It is important that there are many systems based on human embryonic stem cells to study human development that are ethically acceptable. Ultimately, we will use them rather than chimeras of the kind presented here.”