Controversy over creation of monkey-human hybrid embryos

Scientists have obtained 19-day-old embryos with 10,000 cells, 7% of them human

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File image of a person interacting with a chimpanzee
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A team of scientists led by the Spaniard Juan Carlos Izpisua, from the Stalk Institute in the United States, and the Chinese Ji Weizhi, from Kunming University, have created monkey embryos containing human cells. Of the 132 embryos created, three have survived 19 days in the laboratory and have come to form spherical structures of about ten thousand cells, at which point the scientists have stopped development. The work, published in the journal Cell has reopened the controversy over the creation of hybrids between humans and other animals, even more so because of the use of monkeys, which enjoy greater protection than animals such as mice in the field of scientific experimentation.

The authors of the experiment argue that this type of hybrids, known as chimeras can be true laboratories for better understanding embryonic development and the early manifestations of various diseases. They also say they can serve as more realistic models than current ones for testing drugs and, in the future, for growing organs that can be used in human transplants. "As there are experiments that we cannot carry out on humans, it is essential that we have better models to study human biology and the diseases that affect it in a more detailed way," explained Izpisua in a statement. On the ethical dimension of the experiment, the Spanish researcher remarked that "our responsibility as scientists is to carry out research that follows all the ethical, legal and social recommendations". In this case, he assured that "we have consulted and received advice both at institutional level and from independent experts in bioethics, and this exhaustive process has helped us to guide experiments".

In the experiments, scientists fertilised eggs from crab-eating macaque (Macaca fascicularis) developed them in a laboratory culture. Six days later, each embryo made up of 110 monkey cells was injected with 25 human pluripotent cells, that is, cells capable of developing into various cell types in the body. Within a day, there were human cells in 132 of the embryos. Ten days later, 103 of the embryos were still growing. On day 19, only three remained, which were balls of ten thousand cells with 7% human cells. Although regulations vary from country to country, in Spain human embryos cannot currently develop beyond 14 days, which is when the first outline of the nervous system begins to form. Although the experiments have been carried out in China, they would be in a blurred area of the norm because the embryos developed up to 19 days, but the human cells were incorporated on day 6. Regulatory considerations aside, this type of experiment raises questions that go beyond that. To what extent should these embryos be considered human? What should their moral status be?

The work has been received with a diversity of opinions in the scientific community. The biologist Alfonso Martínez Arias, ICREA researcher at the Universitat Pompeu Fabra and professor of genetics at the University of Cambridge, has expressed his doubts to the agency Science Media Center: "In the work there is only an image of a 19-day-old embryo and nothing is discernible, it is impossible to interpret. I think the conclusions they present are not supported by solid data. The results show rather that these chimeras do not work and that all the experimental animals were very sick". On the other hand, he added, "there are many more systems based on human embryonic stem cells to study development that are ethically acceptable". "This is a complicated area that society should think about and discuss before doing experiments. There is a danger that low-quality work could generate a rejection that could affect research," he concluded.

Manuel Serrano, a researcher at the Institute for Research in Biomedicine in Barcelona (IRBB), who last year collaborated with Pierre Savatier of the University of Lyon on a project to create seven-day chimeric embryos between macaque and human, is not so critical. "Scientifically there is nothing revolutionary in this work, because human chimeras in mice, pigs, cows and monkeys have already been done," he explains to ARA. In this work, he adds, "there is an important technical improvement, and this has scientific merit". As for the ethical dimension of the research, Serrano points out that "many researchers are asking for the 14-day margin to be extended". Despite noting that "research is often ahead of ethical regulation", he assures that "scientists want there to be ethical regulations, we do not want to be in a legal vacuum". "Perhaps this work and its impact on the media will serve to stimulate debate and fill the current regulatory vacuum, which takes human embryos into account but not monkey embryos and even less those of mixtures such as this one," he concludes.

According to Gemma Marfany, professor of genetics and member of the Bioethics and Law Observatory of the University of Barcelona, "there are other ways of working with monkey-human hybrid embryos that provide similar information and that do not have ethical problems because the embryos are not viable". He refers, among others, to a study published a month ago in the journal Nature in which chimpanzee-human hybrid embryos were created. "The case of chimeras of pig and human with the aim of obtaining humanised organs for transplants does not generate a serious bioethical problem, because the pig is already an animal that is consumed," he considers. "The macaque, however, is closer and does not have the same size," he says, so that if the objective is to obtain organs, "although it can be discussed, I am not so sure that it is ethically acceptable". In any case, "the aim of this research was rather to know what makes us different and what makes us human," he adds, and, in addition, "these embryos fail because macaques and humans are not close enough".