Scientists ‘open Pandora’s box’ with human-monkey chimeric embryo

Scientists in the US have sparked an ethics row after successfully growing part-human, part-monkey chimeric embryos.

Chimeras are organisms whose cells come from two or more individuals. Interspecies chimeras in mammals have been made since the 1970s, when they were generated in rodents and used to study early developmental processes.

Taking the research a step further, a team at the Salk Institute in California have now produced monkey-human chimeras – by injecting human stem cells into macaque embryos – in petri dishes.

Led by Professor Juan Carlos Izpisua Belmonte, scientists said their work could help to address the severe shortage in transplantable organs as well as help 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,” Prof Izpisua Belmonte said on Thursday.

Six days after the monkey embryos had been created as part of the study, each one was injected with 25 human cells. After one day, human cells were detected in 132 embryos. Ten days later, 103 of the chimeric embryos were still developing.

Survival soon began declining, though, and by day 19, only three chimeras were still alive. But even then, the percentage of human cells in the embryos remained high throughout the time they continued to grow.

According to the scientists, the results, published in the journal Cell, showed that human stem cells “survived and integrated with better relative efficiency than in the previous experiments in pig tissue”.

The team said understanding more about how cells of different species communicate with each other could provide an “unprecedented glimpse into the earliest stages of human development” as well as offer scientists a “powerful tool” for research on regenerative medicine.

However, some ethicists in the UK have raised concerns, saying this type of work “poses significant ethical and legal challenges” and “opens Pandora’s box to human-nonhuman chimeras”.

Commenting on the research, Dr Anna Smajdor, lecturer and researcher in biomedical ethics at the University of East Anglia’s Norwich Medical School, said: “This breakthrough reinforces an increasingly inescapable fact: biological categories are not fixed – they are fluid.

However, she said the new discovery “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’,” she told the PA news agency.

“But whether these embryos are human or not is open to question.”

Prof Izpisua Belmonte maintains that their work has met the 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 added: “Ultimately, we conduct these studies to understand and improve human health.”

Meanwhile, Prof Julian Savulescu, director of the Oxford Uehiro Centre for Practical Ethics and co-director of the Wellcome Centre for Ethics and Humanities, University of Oxford, questioned the study’s morality.

“This research opens Pandora’s box to human-nonhuman chimeras,” he said. “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.”

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

Additional reporting by PA