“Chimera” embryos reignite debate over hybrid animals, especially those involving primates.
A team consisting of Chinese and American scientists has developed embryos from a mixture of human and monkey cells for the first time in history.
The embryos, which were detailed on Thursday in the scientific journal Cell, were created for scientists to uncover new ways to produce organs for people who need transplants.
The researchers injected 25 stem cells from humans, known as induced pluripotent stem cells (or ISP cells), into embryos from macaque monkeys. The scientists then grew the mixed embryos in test tubes for up to 20 days in order to study how the animal and human cells communicate with one another.
The idea behind the research is to determine whether or not monkey’s could eventually be able to grow human organs for transplants. According to the team of scientists, thousands of people die every year waiting for such transplants.
The mixed-species embryos are referred to as chimeras, for the fire-breathing she-monster in Greek mythology having a lion’s head, a goat’s body, and a serpent’s tail. The chimeras were studied for up to 20 days after they were created.
The scientists were led by Prof Juan Carlos Izpisua Belmonte of the Salk Institute in the US, who, in 2017, helped make the first human-pig hybrid.
Their work could pave the way in addressing the severe shortage in transplantable organs as well as help understand more about early human development, disease progression and ageing, he said.
“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 maintained that the study, published in the journal Cell, had met the current ethical and legal guidelines.
“Ultimately, we conduct these studies to understand and improve human health,” he said.
While work of this type could lead to a solution to the critical problem of transplant organ shortages, ethical questions abound.
Specifically, critics worry that human cells could become part of the developing brain of such an embryo and of the brain of the resulting animal.
“Should it be regulated as human because it has a significant proportion of human cells in it? Or should it be regulated just as an animal? Or something else?” Rice University’s Matthews said. “At what point are you taking something and using it for organs when it actually is starting to think and have logic?”
Another concern is that using human cells in this way could produce animals that have human sperm or eggs.
“Nobody really wants monkeys walking around with human eggs and human sperm inside them,” said Hank Greely, a Stanford University bioethicist who co-wrote an article in the same issue of the journal that critiques the line of research while noting that this particular study was ethically done. “Because if a monkey with human sperm meets a monkey with human eggs, nobody wants a human embryo inside a monkey’s uterus.”
Another critique of this particular study centered on its use of primates.
Some question the need for such experiments using closely related primates — these animals are not likely to be used as model animals in the way that mice and rodents are. Nonhuman primates are protected by stricter research ethics rules than are rodents, and they worry such work is likely to stoke public opposition.
“There are much more sensible experiments in this area of chimaeras as a source of organs and tissues,” says Alfonso Martinez Arias, a developmental biologist at Pompeu Fabra University in Barcelona, Spain. Experiments with livestock animals, such as pigs and cows, are “more promising and do not risk challenging ethical boundaries”, he says. “There is a whole field of organoids, which can hopefully do away with animal research.”
Interestingly, human-human chimeras have been identified. In fact, the recent advances in DNA testing have resulted in some shocking discoveries for the affected individuals.
Scientific American explains that, when a mother is carrying fraternal twins, one of the embryos might die very early in the pregnancy. Then, the other embryo can absorb some cells from the deceased one. The resulting baby ends up with two sets of DNA.
Sometimes these chimeras make the news.
In 2015, a man from Washington took a cheek swab paternity test that said he was technically his son’s uncle, not his father. Further testing revealed that the man had different DNA in his saliva and his sperm. Genetic experts believed he was a human chimera, and he had absorbed some of his DNA from a fraternal twin’s embryo, BuzzFeed reported.
A woman named Karen Keegan wound up in a similar situation. Tests said she wasn’t the biological mother of her children, but it turned out that the DNA in her blood was different than the DNA in her ovaries. Doctors said her extra DNA most likely came from a fraternal twin — and in 2002 her story became a report in the New England Journal of Medicine.
The following video reviews human chimeras, for those of you who would like more background on this subject.DONATE
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