Scientists introduced human stem cells into monkey embryos and created the first chimeric embryos, which they managed to preserve for 20 days. This is an American-Chinese team of researchers who created the 2017 the first human-pig hybrids, with a short lifespan and a very small presence of human cells, as then only one in 100.000 cells of the chimeric embryo was human.
Now human-monkey chimeras have been created, which not only lived for about three weeks, but also contained a very large amount of human cells. The chimeras got their name from «Chimera "of Greek mythology that exuded fire, had the body of a goat, the head of a lion, and its tail ended in a snake. These are organisms whose cells come from two or more "units". In this case they come from different species: a long-haired macaque and a man.
Many scientists express concern, noting that such research raises serious issues and concerns at the level of bioethics, especially if other researchers try to preserve chimeric embryos for even longer.
In recent years, researchers have produced pig embryos and sheep embryos that contained human cells. This research is said to be important as it could one day allow them to develop human organs in other animals, increasing the number of organs available for transplantation.
Scientists have now confirmed that they have produced macaque embryos containing human cells, revealing that the cells could survive and even multiply.
In addition, the researchers - led by the professor Juan Carlos Izpisua Belmonte from the Salk Institute in the USA - say that these results can help to better understand early human development and evolution of primates and to develop effective strategies for improving human chimerism in evolutionarily distant species.
"Our goal is not to create a new organism, not even a monster", said Belmonte. "And we do not do that. "We are trying to understand how cells from different organisms communicate with each other."
The investigation confirms the rumors reported by the Spanish newspaper "The country" in 2019, that a team of researchers led by Belmonte had produced human ape chimeras. The research, published in the journal "Cell", reveals how scientists got specific human embryonic cells called fibroblasts and reprogrammed them to become stem cells. These were then inserted into 132 long-lived macaque embryos, six days after fertilization.
The embryos were allowed to grow in Petri dishes and terminated 19 days after stem cell injection. To test whether the embryos contained human cells, the team designed human stems to produce a fluorescent protein.
Among other findings, the results showed that all 132 embryos contained human cells on the seventh day after fertilization, although as they developed the percentage that contained human cells, this decreased over time.
The team also reported finding some differences in the interactions of human cells and these monkeys within chimeric embryos, compared to the embryos of monkeys without human cells.
Dr Jun Wu, co-author of the research, he said hopes the research will help develop "transplantable human tissues and organs in pigs to overcome the shortage of donor organs worldwide".
This research raises ethical concerns. Professor Julian Savulescu, director of the Uehiro Oxford Center for Ethical Practice and co-director of the Center for Ethics and Humanities at Oxford University, said: the investigation opened Pandora's box in human-non-human chimeras.
Others expressed concerns about quality of the study. Dr Alfonso Martinez Arias, an associate lecturer in the Department of Genetics at the University of Cambridge, said: "I do not think the conclusions are supported by solid data. "The results, as far as can be interpreted, show that these chimeras do not work and that all the experimental animals are very sick."
The first chimeras between different species of mammals were created in the laboratory in the 1970s. Experts agree that relevant research, despite its - controversial - advances, is still in its infancy and that chimeras need to become much healthier and more effective in order to be relevant to future biomedical studies.
Next month the International Society for Stem Cell Research (ISSCR) It is expected to release its revised guidelines on how relevant research should be conducted, including on chimeras. Until now, scientists have been banned from letting human-animal chimeras mate.