Human-monkey Chimeric Embryos Set off Ethics Debate
A study published in the journal Cell has announced the creation of human-monkey chimeric embryos, igniting renewed debate over ethics.
The embryos are known as chimeras, organisms whose cells come from two or more “individuals”, and in this case, different species: a long-tailed macaque and a human. The research confirmed that the cells can survive and multiply.
Natural human chimeras do exist, and can involve humans cells from two embryos in the same womb fusing to produce a single individual, or a combination of maternal and foetal cells, or monozygotic twins sharing blood cells from a shared placenta.
Previously, researchers had produced pig or sheep embryos that contained human cells, in an effort to one day develop a way to grow human organs for transplant inside the animals.
The researchers, led by Prof Juan Carlos Izpisua Belmonte from the Salk Institute in the US, said that the results shed new light on the communications pathways between cells of different species. This could help with future efforts to engineer chimeras using more distantly related species.
“These results may help to better understand early human development and primate evolution and develop effective strategies to improve human chimerism in evolutionarily distant species,” the authors wrote.
In 2019, the Spanish newspaper El País reported on rumours that a team of researchers led by Belmonte had created monkey-human chimeras.
Specific human foetal cells called fibroblasts were reprogrammed to become stem cells, and were then introduced into 132 embryos of long-tailed macaques, six days after fertilisation.
“Twenty-five human cells were injected and on average we observed around 4% of human cells in the monkey epiblast,” said Dr Jun Wu, a co-author of the research, and now at the University of Texas Southwestern Medical Center.
The embryos were grown in petri dishes and were terminated 19 days after the stem cells were injected. The human cells were engineered with a fluorescent protein to enable identification.
The researchers reported that 132 embryos contained human cells on day seven after fertilisation. However, the proportion containing human cells fell over time.
“We demonstrated that the human stem cells survived and generated additional cells, as would happen normally as primate embryos develop and form the layers of cells that eventually lead to all of an animal’s organs,” Belmonte said.
The researchers also found differences in intercellular interactions between human and monkey cells within chimeric embryos, compared to the normal monkey embryos.
The researchers hoped the research would help develop “transplantable human tissues and organs in pigs to help overcome the shortages of donor organs worldwide”, said Wu.
Prof Robin Lovell-Badge, a developmental biologist from the Francis Crick Institute in London, said at the time of the El País report he was not concerned about the ethics of the experiment, noting the team had only produced a ball of cells. But he noted conundrums could arise in the future should the embryos be allowed to develop further.
While not the first attempt at making human-monkey chimeras – another group reported such experiments last year – the new study has reignited such concerns. Prof Julian Savulescu, the director of the Oxford Uehiro Centre for Practical Ethics and co-director of the Wellcome Centre for Ethics and Humanities at the University of Oxford, said the research had raised all sorts of ethical concerns.
“These embryos were destroyed at 20 days of development but it is only a matter of time before human-nonhuman chimeras are successfully developed, perhaps as a source of organs for humans,” he said, and added that a key ethical concern was the moral status of such organisms.
“Before any experiments are performed on live-born chimeras, or their organs extracted, it is essential that their mental capacities and lives are properly assessed. What looks like a nonhuman animal may mentally be close to a human,” he said. “We will need new ways to understand animals, their mental lives and relationships before they are used for human benefit.”
Others were less concerned, and rather pointed out that all the study found was that the creation of such chimera was simply ineffective.
Dr Alfonso Martinez Arias, an affiliated lecturer in the department of genetics at the University of Cambridge, said: “I do not think that the conclusions are backed up by solid data. The results, in so far as they can be interpreted, show that these chimeras do not work and that all experimental animals are very sick.
“Importantly, there are many systems based on human embryonic stem cells to study human development that are ethically acceptable and in the end, we shall use this rather than chimeras of the kind suggested here.”
Source: The Guardian
