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Human cells grown in monkey embryos raise ethical concerns

A human-monkey blastocyst, an early stage of embryo development

Weizhi Ji, Kunming University of Science and Technology

Researchers have grown human cells in monkey embryos with the aim of understanding more about how cells develop and communicate with each other.

Juan Carlos Izpisua Belmonte at the Salk Institute in California and his colleagues have produced what are known as human-monkey chimeras, with human stem cells – special cells that have the ability to develop into many different cell types – inserted in macaque embryos in petri dishes in the lab.

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However, some ethicists have raised concerns, saying this type of work “poses significant ethical and legal challenges”.

Chimeras are organisms whose cells come from two or more individuals. In humans, chimerism can naturally occur following organ transplants, where cells from that organ start growing in other parts of the body.

Izpisua Belmonte says the team’s work could pave the way in addressing the severe shortage in transplantable organs, as well as help us understand more about early human development, disease progression and ageing. “These chimeric approaches could be really very useful for advancing biomedical research not just at the very earliest stage of life, but also the latest stage of life,” he said.

In 2017, Izpisua Belmonte and his colleagues created the first human-pig chimera, where they incorporated human cells into early-stage pig tissue but found that human cells in this environment had poor molecular communication. So the team decided to investigate lab-grown chimeras using a more closely related species: macaques.

The human-monkey chimeric embryos were monitored in the lab for 19 days before being destroyed. The team says the human stem cells “survived and integrated with better relative efficiency than in the previous experiments in pig tissue”.

Izpisua Belmonte says the work meets current ethical and legal guidelines. “As important for health and research as we think these results are, the way we conducted this work, with utmost attention to ethical considerations and by coordinating closely with regulatory agencies, is equally important.”

“This breakthrough reinforces an increasingly inescapable fact: biological categories are not fixed – they are fluid,” said Anna Smajdor at the University of East Anglia, UK, in a statement. “This poses significant ethical and legal challenges.”

“The scientists behind this research state that these chimeric embryos offer new opportunities, because ‘we are unable to conduct certain types of experiments in humans’. But whether these embryos are human or not is open to question,” she said.

Julian Savulescu at the University of Oxford said in a statement: “This research opens Pandora’s box to human-nonhuman chimeras. 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. That is one of the long-term goals of this research.”

“The key ethical question is: what is the moral status of these novel creatures?” he said. “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.”

Journal reference: Cell, DOI: 10.1016/j.cell.2021.03.020

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