Scientists have successfully grown monkey embryos containing human cells.
In a paper published in Cell, a research team outlined how it produced what are known as human-monkey chimeras with human stem cells inserted into macaque embryos in the lab.
Juan Carlos Izpisua Belmonte at the Salk Institute in California, who led the team, said the study could help to advance biomedical research at both early and later stages of life.
Chimeras are organisms whose cells come from two or more individuals. The applications for such science includes producing lab-grown human organs, which could help with the supply needs for transplant patients.
Izpisua Belmonte and his team previously created the first human-pig chimera, incorporating human cells into early-stage pig tissue. However, this proved to be unsuccessful as they found that human cells in this environment had poor molecular communication.
In the case of the macaque embryos, the team was able to monitor them in the lab for 19 days before they were destroyed.
According to the study, human cells were detected in 132 chimeric embryos after one day. After 10 days, 103 of the embryos were still developing. Survival then began declining and by day 19, only three chimeras were still alive.
Opening Pandora’s box
While heralded as a major breakthrough, the research has also raised several ethical concerns in the scientific community.
University of Oxford’s Prof Julian Savulescu, who specialises in bioethics, said the most difficult issue lies in the future. “This research opens Pandora’s box to human-nonhuman chimeras,” 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. What looks like a nonhuman animal may mentally be close to a human. We will need new ways to understand animals, their mental lives and relationships before they used for human benefit.
“Perhaps this will lead us to rethink how animals are treated more generally by humans in science, medicine and agriculture.”
University of Cambridge’s Dr Alfonso Martinez Arias also raised questions about the results of the study.
“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,” he said. “This complicated area in which, as in the case of the CRISPR babies, society should think and discuss before doing experiments.”
Marinez Arias was referring to a Chinese clinical trial that intended to create the first gene-edited babies using CRISPR, a gene-editing technology that boasts potential game-changing benefits as well as concerning side effects.
Following massive backlash, the scientist behind the trial, He Jiankui, defended his decision and said he felt proud of what he had done. He was later sentenced to three years in prison for violating medical regulations.
Izpisua Belmonte, who has previously used CRISPR in his work, acknowledged the ethical concerns around his most recent work with human-monkey embryos, but added that it 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,” he said.
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