Chimera alert? Myths and facts of human-non-human animal hybrids in medicine

By David Warmflash, MD | 1 July 2015
Genetic Literacy Project

(Photographer: Armin Kübelbeck, CC-BY-SA, Wikimedia Commons)

Throughout history, people have been fascinated by the idea of combined creatures, such as the legendary Chimera, which Homer’s Iliad describes as being part lion, part goat, and part snake. In particular, we like to imagine fusion creatures with a human component, a classic example being Greek mythology’s centaurs and centraurides, with a human head and torso merged with the body and legs of a horse.

In children’s tales in modern times, we have the mermaids, like Ariel, the Little Mermaid, a great success for the Disney company, not only as an animated film but as inspiration for numerous dolls for little girls planet wide.

We ask children, and sometimes adults, to describe what kind of non-human animal they’d like to be if they could. It’s an exciting idea to think about human-non-human combinations, and science has actually begun experimenting in this area genetically for the sake of improving human health. Such research is not aimed at producing a centaur, nor any other being that’s anatomically part human and part something else, but the field of human-animal hybridization research scares people anyway.

In our society, where genetic technology is ever more influential, the fact that people are concerned is a good thing. Ethicists and scientists say that we should be extremely careful. A few years ago, Stanford University hosted a major conference focussed on this issue; the proceedings were published in the Stanford Journal of Animal Law and Policy. It stressed caution. That means not creating literal chimera, like a human head on a horse body. This is not something that geneticists even know how to do, since the genes and their on-off switches controlling development of a new organism on the level of gross body parts number in the tens of thousands.

But since not all people understand this—and because there’s a paranoid, sensationalist element in some media, and, every now and then, some individual, or institution, might engage in unethical research—there’s a fear based on the belief that human-animal hybridization research could lead to making centaurs and other such fantastical beings. So on the less obvious end, being careful in human-animal hybridization research also means educating the public not to think that fantastical beings are in our near future.

Paranoia on the web

Taking out of context reports about research combining human and non-human cells and genes to make novel tissues and organs, some posts floating around the internet use the term “chimera” to describe what scientists are developing, and go as far as to imply that literal chimera have already been created. The only reason we do not know about it, they say, is because there is a conspiracy to keep it quiet. Here’s an example of comments from a website that turns up near the top of the list when one searches for the term “human-animal hybrids”.

Apparently, it is now even possible to grow entire human organs inside animals. In fact, scientists in Japan plan to start systematically growing human organs inside of pigs within 12 months. The goal is to increase the number of organs available for medical transplants. But once a human organ is grown inside a pig, that pig is no longer fully a pig. And without a doubt, that organ will no longer be a fully human organ after it is grown inside the pig. Those receiving those organs will be allowing human-animal hybrid organs to be implanted into them.

The same site also expresses concern about the insertion of a human chromosome into mouse cells and the use of human embryonic stem cells to enhance the brains of mice, making them smarter. But the key to how misconstrued the content is comes when the writer states that the human organ makes the pig “no longer fully a pig”, and then implies that somehow the recipient receiving such a graft becomes part pig.

But getting a human organ that’s been engineered, enhanced, or otherwise developed in a laboratory setting, and then grown or maintained connected to the blood supply of a pig, would not prompt any of us to oink, or start rolling around in the mud, any more than a blood transfusion from LeBron James or Kevin Durant could suddenly make you a scoring terror in the NBA. Blood doesn’t doesn’t improve athletic ability and neither does a transplanted kidney—whether the kidney has been maintained within a pig, or for that matter even if the kidney is literally a pig kidney, produced in the natural way within the pig’s body. The kidney’s job is to filter the blood and even in the case of xenotransplantation—getting organs directly from a non-human animal—the main issue is whether the organ can be protected from rejection by the recipient’s immune system.

How science is really using human-non-human hybrids

One fascinating hybrid product is the engineering of pigs to make human blood. These experiments have been conducted at the Mayo Clinic in Minnesota to help scientists understand how viral infections can transfer between humans and non-human animals. It’s extremely relevant to current medicine, given how the human immunodeficiency virus (HIV) that causes AIDS is thought to have entered the human population from chimpanzees and that species of Ebola virus, responsible for the current Ebola outbreak in West Africa, is thought to have come from bushmeat animals, particularly bats.

To grow human stem cells, one key method is to create a cell hybrid using genetic information from a human cell inside a de-nucleated (nucleus removed) egg cell from an animal, such as a rabbit. This does not produce a creature with a human mind and also long, furry ears, but it is moving stem cell research in the direction of being able to treat a plethora of human diseases.

Researchers at the Salk Institute in La Jolla, Calif., have combined mouse-human livers to study liver disease in mice that previously were not a good model for human liver disease. No humans with tails are walking around the lab, nor are there any talking mice, but the mice are humanized when it comes to their livers. For this reason, the special mice can be infected with human hepatitis viruses, whereas naturally occurring mice cannot. Also, since the malaria parasite that kills millions or people around the world gets into the human liver, the special mice also are becoming vital in the effort to develop new malaria drugs.

One area of research that particularly irks the “watch out for human-chimera” paranoid type people is the mouse-human brain. Developed by researchers at Stanford University, it involves mice whose brains have a small percentage of human cells. The mice are not inventing warp drive, but they are helping neuroscientists to make great strides toward treating, and possibly preventing, neurodegenerative diseases, like Parkinson and Alzheimer diseases.

Perhaps one of the most fascinating, and potentially live saving, projects on the clinical horizon is the effort to grow human organs within non-human animals, such as pigs and rats. Such a project involving pigs is underway in Japan. The idea is that it may solve the problem of organ shortages around the planet for people needing transplants. According the US Department of Health and Human Services, more than 123,000 people in the United States currently need an organ transplant, and about 21 people die each day waiting for one.

Xenotransplantation—using organ grafts from non-human animals—is a possible solution, but the less human the organ the more likely the recipient is to suffer from organ rejection by the immune system. But simply using the animal body as a bay for maintaining fully organs until needed is another matter, and the effort now is to grow the human organ, or humanized animal organ, within the animal and leave it there until needed.

Reprinted with permission from the author.

David Warmflash is an astrobiologist and science writer. He received his M.D. from Tel Aviv University Sackler School of Medicine, and has done post doctoral work at Brandeis University, the University of Pennsylvania, and the NASA Johnson Space Center, where he was part of the NASA’s first cohort of astrobiology training fellows. Dr. Warmflash has written numerous articles covering a range of science topics, from the search for extraterrestrial life and space exploration to the origins of life, genetics, neuroscience, biotechnology, and the history of science. His articles have appeared in various publications, including Wired UK, Discover, Scientific American, Genetic Literacy Project, and Cricket Media. Throughout 2018, he did a blog post series on the emergence of ancient science for Vision Learning, covering thinkers from history. Many of these ancient pioneers of science also make an appearance in his book, “Moon: An Illustrated History: From Ancient Myths to the Colonies of Tomorrow”. Follow him on Twitter @CosmicEvolution.

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