Skip to main content

Science of the Lambs: We can now grow human cells in sheep

chimera sheep tongue
N-Sky/Getty Images
N-Sky/Getty Images

Strange creatures have emerged from Pablo Ross’s University of California, Davis lab. They’re neither strictly sheep nor fully human. Instead, they’re a bit of both.

In a biotech breakthrough — the second of its kind in just over a year — Ross announced at the American Association for the Advancement of Science last week that he and his colleagues have successfully grown nonhuman animal embryos that contain human cells. Previously, the host species were pigs. Now, they’re sheep.

They have the potential to revolutionize organ transplantation and help save thousands of lives.

These human-animal hybrids, or interspecies chimeras, are not just the product of bizarre experimentation done for the sake of science. They have the potential to revolutionize organ transplantation and help save thousands of lives each year in America and around the globe.

Though this breakthrough brings us one step closer to growing transplant organs inside host animals, it also comes with some ethical baggage. Bioethicists and animal advocates alike question whether human-animal hybrid studies are worth the potential cost of animal welfare or the risk of creating nonhuman animals with humanlike qualities.

Why chimeras?

There’s an organ shortage in America that sees approximately twenty people die while waiting for a transplant every day, according to the U.S. Department of Health and Human Services. Minus the roughly 16,000 suitable donors and 33,600 transplants in 2015, nearly patients 120,000 remained on the waiting list. In the simplest terms, there isn’t enough organ supply to satisfy demand.

(Salk Institute)
A pig embryo injected with human stem cells that grew to be four weeks old.(Salk Institute)

“Organ transplantation has been extremely successful and saves a lot of lives,” Ross, a UC Davis animal scientist, told Digital Trends. “The problem is there are those that get the organs and those that don’t, because there are not enough organs for transplant.”

But, if scientists were able to grow human organs inside host animals, they could potentially generate enough organs to eliminate the shortage all together, saving thousands of lives annually in the U.S. alone.

New findings highlight promise of chimeric organisms for science and medicine

Prior chimera studies, including one in which scientists grew a rat pancreas inside a mouse, give evidence for this approach. But human organs are much bigger than rats’, so Ross and his colleagues have had to focus on larger livestock.

“If we want to grow a human organ we’ll have to go to an animal larger than a mouse or a rat,” he said. “Pigs and sheep have some important characteristics that would make them a good host species for growing the human organ.”

“If we want to grow a human organ we’ll have to go to an animal larger than a mouse or a rat.”

For one thing, pig and sheep organs are similar in size and shape to an adult human’s. And, since they grow relatively quickly, certain organs can be essentially grown to order. Recent advances in genetic engineering make scientists optimistic that they can even genetically tailor organs to be more compatible with their human recipients.

“This is a first step in a long series of stages to eventually get to an actual complete human organ that will develop in a live born sheep,” Insoo Hyun, a bioethicist from Case Western Reserve University who was not involved in the study, told Digital Trends. “It would then hopefully make it all the way to adulthood and make it large enough for transplantation.”

How it’s done

Human-animal hybrids may have a long mythical history, but scientifically they’re pretty new. Just last year, Ross and his colleagues made a splash when they published a report in the journal Cell that showed they’d successfully developed a pig embryo with human cells. The host embryos didn’t have many human cells — just about one in 100,000 — but the survival of even just a few made for groundbreaking research. DNA analysis suggested that the recent sheep embryos reached a ratio of about one human cell in 10,000 cells, according to Ross, which is progress but still not efficient enough to successfully grow transplantable organs.

Genome Editing with CRISPR-Cas9

Here’s how the recent research worked.

To begin, scientists injected human stem cells into an early-stage sheep embryo. At about a week old, they then implanted that chimeric embryo into a female sheep and let it develop for 28 days. After those four weeks, the researchers euthanized the sheep and ran DNA analyses on the chimeric embryos to see how well the human stem cells developed.

Thanks to advances in genetic engineering, scientists can use gene editing tools like CRISPR to create host animals that develop without a specific organ. This way, the injected human stem cells fill the void of the missing organ, and develop into the desired organ as the embryo matures.

“We don’t know which type of human stem cells could have this property of making a chimera.”

“What we’ll need at that location at that specific time are human cells that have to be precisely there to respond to that need for pancreas formation,” Ross said. “And those human cells won’t have competition from the pig or sheep cells. You need the cells at precisely that moment which means you’ll need the cells kind of randomly across the whole body because we cannot yet direct the cells to only be there and nowhere else.”

One of the big questions now is which human stem cells are the most successfully adaptive.

“We don’t know which type of human stem cells could have this property of making a chimera, specifically an interspecies chimera,” Ross said.

Facing controversy

Human-animal chimera studies are controversial but they’re gaining favor. In 2016, the National Institute of Health (NIH) announced plans to lift its moratorium on such research.

Still, animal welfare advocates worry that these studies infringe on the well-being of the test subjects. Bioethicists also worry that these experiments could lead to the development of unusually human-like creatures.

Statistic Brain Research Institute

An important consideration, as Hyun stated, is “whether or not you are creating large animals that are more or less biologically human in important respects or may have a status that is a little higher morally than a normal sheep.

“There’s the concern that these types of experiments create morally ambiguous beings,” he added. “We know what sheep are and we know what people are, but what about sheep that have large contributions of human cells or an entire human organ? That’s a new thing, where does it fall on the spectrum?”

Hyun said his personal concerns center around animal welfare, that the subjects are living comfortably and being treated humanely.

“The concerns about the personhood of an animal, [as long as] we’re staying away from the brain, is not yet an issue to worry about,” he said.

“I don’t have the statistic for the number of animals slaughtered for bacon everyday but it’s significantly more.”

Ross recognized the importance of these concerns and stressed that all of their research is performed under biomedical research oversight and regulation. However, when it comes to the concern about creating animals that are more or less biologically human, Ross pointed to previous research that suggested host species still grow their species-specific organ, irrespective of the introduced stem cells.

“But at the same time, because we’re scientists, we’re not just going to go with what we believe or expect to happen,” he said “We want to measure that. We want to produce scientific information to inform whether this is something acceptable or not.”

As for animal welfare concerns, Ross stressed that the animals in these cases would be treated humanely and would provide a tremendous benefit to society that, for many, may outweigh the downside.

“If this [research] becomes successful, there is a concern about using animals for human benefit,” he said. “But you have to consider that we use large animals for food, work, clothing, and emotional comfort. I don’t have the statistic for the number of animals slaughtered for bacon everyday but it’s significantly more [than those that would be used for organ transplant]. Several orders of magnitude more. That’s a choice the public will have to make.”

Editors' Recommendations

Dyllan Furness
Dyllan Furness is a freelance writer from Florida. He covers strange science and emerging tech for Digital Trends, focusing…
Digital Trends’ Tech For Change CES 2023 Awards
Digital Trends CES 2023 Tech For Change Award Winners Feature

CES is more than just a neon-drenched show-and-tell session for the world’s biggest tech manufacturers. More and more, it’s also a place where companies showcase innovations that could truly make the world a better place — and at CES 2023, this type of tech was on full display. We saw everything from accessibility-minded PS5 controllers to pedal-powered smart desks. But of all the amazing innovations on display this year, these three impressed us the most:

Samsung's Relumino Mode
Across the globe, roughly 300 million people suffer from moderate to severe vision loss, and generally speaking, most TVs don’t take that into account. So in an effort to make television more accessible and enjoyable for those millions of people suffering from impaired vision, Samsung is adding a new picture mode to many of its new TVs.
[CES 2023] Relumino Mode: Innovation for every need | Samsung
Relumino Mode, as it’s called, works by adding a bunch of different visual filters to the picture simultaneously. Outlines of people and objects on screen are highlighted, the contrast and brightness of the overall picture are cranked up, and extra sharpness is applied to everything. The resulting video would likely look strange to people with normal vision, but for folks with low vision, it should look clearer and closer to "normal" than it otherwise would.
Excitingly, since Relumino Mode is ultimately just a clever software trick, this technology could theoretically be pushed out via a software update and installed on millions of existing Samsung TVs -- not just new and recently purchased ones.

Read more
AI turned Breaking Bad into an anime — and it’s terrifying
Split image of Breaking Bad anime characters.

These days, it seems like there's nothing AI programs can't do. Thanks to advancements in artificial intelligence, deepfakes have done digital "face-offs" with Hollywood celebrities in films and TV shows, VFX artists can de-age actors almost instantly, and ChatGPT has learned how to write big-budget screenplays in the blink of an eye. Pretty soon, AI will probably decide who wins at the Oscars.

Within the past year, AI has also been used to generate beautiful works of art in seconds, creating a viral new trend and causing a boon for fan artists everywhere. TikTok user @cyborgism recently broke the internet by posting a clip featuring many AI-generated pictures of Breaking Bad. The theme here is that the characters are depicted as anime characters straight out of the 1980s, and the result is concerning to say the least. Depending on your viewpoint, Breaking Bad AI (my unofficial name for it) shows how technology can either threaten the integrity of original works of art or nurture artistic expression.
What if AI created Breaking Bad as a 1980s anime?
Playing over Metro Boomin's rap remix of the famous "I am the one who knocks" monologue, the video features images of the cast that range from shockingly realistic to full-on exaggerated. The clip currently has over 65,000 likes on TikTok alone, and many other users have shared their thoughts on the art. One user wrote, "Regardless of the repercussions on the entertainment industry, I can't wait for AI to be advanced enough to animate the whole show like this."

Read more
4 simple pieces of tech that helped me run my first marathon
Garmin Forerunner 955 Solar displaying pace information.

The fitness world is littered with opportunities to buy tech aimed at enhancing your physical performance. No matter your sport of choice or personal goals, there's a deep rabbit hole you can go down. It'll cost plenty of money, but the gains can be marginal -- and can honestly just be a distraction from what you should actually be focused on. Running is certainly susceptible to this.

A few months ago, I ran my first-ever marathon. It was an incredible accomplishment I had no idea I'd ever be able to reach, and it's now going to be the first of many I run in my lifetime. And despite my deep-rooted history in tech, and the endless opportunities for being baited into gearing myself up with every last product to help me get through the marathon, I went with a rather simple approach.

Read more