A part-human, part-pig embryo. It sounds like science fiction, but it’s not.
At a lab in California, researchers successfully took human stem cells and transplanted them into pig embryos, and let them grow for several weeks.
It’s what science calls a “chimera,” after the creature from Greek mythology that is part lion, part goat, with a tail that sometimes ends in a snake’s head.
But, chimeras are controversial in science because of ethical concerns surrounding animal rights and human hybrids.
This study was done at the Salk Institute and the study was published Jan. 26 in the journal Cell.
“The eventual, sort of, super long-term goal is to develop human organs that have been grown in a non-human animal host, but that are as human as can be,” according to Jason Robert, a bioethicist at ASU who has followed the debate around chimeras for the last 15 years.
For example, he said, imagine growing a human liver in the body of a non-human animal and hope that it will be recognized as a human organ when it’s transplanted in a human body.
That could help overcome the massive gap between the number of people who need organ transplants in the country and the organs available, he said.
We’re not very close to achieving that at this point, Robert said, but there are some other, more short-term goals that this kind of research is accomplishing. He said that they’re also working to develop animal models for human diseases to help with potential drug discoveries and new treatments.
He said that the reason this study was so groundbreaking is that it showed us that, in order to create something that can treat human conditions, we have to use animals that are pretty close to humans, like pigs, or, potentially primates. Most of this research has been done with rodents in the past.
But, those concerned with animal rights aren’t going to be too happy about having them serve as a host for human organs who could be terminated at any time.
And, then there’s the sci-fi concern.
Robert said that even if we can accept that sometimes animal research is morally justified, there have been other concerns raised over the years, primarily by scientists themselves.
“One is that the chimerization would allow for the human cells to get into the gonads, and therefore, potentially, into the germ line,” he said, which could result in the science-fiction scenarios people worry about.
“There’s a possibility for some serious unintended consequences,” he said. The gonads is one of the areas scientists have been worried about, “and the other is the brain,” he said.
There’s a concern that an animal’s brain could exhibit some of the characteristics of human cognition and human emotion, “that might make it the case that we never should have created the creature in the first place, because it’s just so cruel,” he said.
Scientists have taken careful steps avoid this, though, he said. They select cells that are not likely to “run amuck,” he said. And, they keep the number of human cells relatively small so that they don’t have to worry about a high percentage of human cells doing anything in the brain of chimera.
“If we want to learn something that’s really valuable from these chimeras, we’re going to want them to be as human as possible,” Robert said, so that we can create real solutions for human disease. “But, at the same time, the deep ethical concern is that the animals could become too human.”
And that’s a really tough balance to strike.
In this study in California, he said, the work was done slowly and with a lot of thought about what some of the ethical implications might be. But, he said, what’s being published may be just scratching the surface of the work that’s underway on this around the world.
“So I think we’ve got a lot of grappling with chimeras to do into the future,” he said.
