For once, the yeuk factor is real

From the MIT Technology Review today.

" ...  MIT Technology Review estimates that about 20 pregnancies of pig-human or sheep-human chimeras have been established during the last 12 months in the U.S."

So how does that work?

"By modifying genes, scientists can now easily change the DNA in pig or sheep embryos so that they are genetically incapable of forming a specific tissue. Then, by adding stem cells from a person, they hope the human cells will take over the job of forming the missing organ, which could then be harvested from the animal for use in a transplant operation.

“We can make an animal without a heart. We have engineered pigs that lack skeletal muscles and blood vessels,” says Daniel Garry, a cardiologist who leads a chimera project at the University of Minnesota. While such pigs aren’t viable, they can develop properly if a few cells are added from a normal pig embryo. Garry says he’s already melded two pigs in this way and recently won a $1.4 million grant from the U.S. Army, which funds some biomedical research, to try to grow human hearts in swine."

OK, there's a yeuk factor there, but surely if the objectives are good .. ?

"The worry is that the animals might turn out to be a little too human for comfort, say ending up with human reproductive cells, patches of people hair, or just higher intelligence. “We are not near the island of Dr. Moreau, but science moves fast,” NIH ethicist David Resnik said during the agency’s November meeting. “The specter of an intelligent mouse stuck in a laboratory somewhere screaming ‘I want to get out’ would be very troubling to people.”

Oh yes, the screaming mouse.

"... Desperately ill people on organ waiting lists might someday order a chimera and wait less than a year for their own custom organ to be ready. “I really don’t see much risk to society,” he says.

"Before that can happen, scientists will have to prove that human cells can really multiply and contribute effectively to the bodies of farm animals. That could be challenging since, unlike rats and mice, which are fairly close genetically, humans and pigs last shared an ancestor nearly 90 million years ago.

"To find out, researchers in 2014 decided to begin impregnating farm animals with human-animal embryos, says Pablo Ross, a veterinarian and developmental biologist at the University of California, Davis, where some of the animals are being housed. Ross says at Davis he has transferred about six sets of pig-human embryos into sows in collaboration with the Salk Institute and established another eight or 10 pregnancies of sheep-human embryos with Nakauchi. Another three dozen pig transfers have taken place outside the U.S., he says.

"These early efforts aren’t yet to make organs, says Ross, but more “to determine the ideal conditions for generating human-animal chimeras.” The studies at Davis began only after a review by three different ethics committees, and even then, he says, the university decided to be cautious and limit the time the animals would be allowed to develop to just 28 days (a pig is born in 114 days).

"By then, the embryonic pig is only half an inch long, though that’s developed enough to check if human cells are contributing to its rudimentary organs.

“We don’t want to grow them to stages we don’t need to, since that would be more controversial,” says Ross. “My view is that the contribution of human cells is going to be minimal, maybe 3 percent, maybe 5 percent. But what if they contributed to 100 percent of the brain? What if the embryo that develops is mostly human? It’s something that we don’t expect, but no one has done this experiment, so we can’t rule it out.”

So run that past me again ...

 “My view is that the contribution of human cells is going to be minimal, maybe 3 percent, maybe 5 percent. But what if they contributed to 100 percent of the brain? What if the embryo that develops is mostly human? It’s something that we don’t expect, but no one has done this experiment, so we can’t rule it out.”

If a pig-embryo can have its kidney developmental genes knocked out, so growing kidneys constructed from stem cells from a specific person - so that less than a year later there's a non-rejectable transplant available. Well,  it's going to happen.

My question: are we happy to eat the bacon sandwich made from the rest of the pig?