Scientists have successfully created the first human-animal hybrid — sort of.
According to National Geographic, scientists have created an embyro that is 0.01% human.
"Building on a controversial breakthrough made in 2017, scientists announced on Saturday that they have created the second successful human-animal hybrids: sheep embryos that are are 0.01-percent human by cell count," reports NG. "The embryos, which were not allowed to develop past 28 days of age, move researchers a small step closer to perhaps growing human organs for medical transplant."
The motivation for the hybrids was to potentially grow human organs in animals such as pigs or sheep for the purpose of organ transplants.
"Every hour, six people in the United States are added to the national waiting list for organ transplants—and each day, 22 people on the list die waiting," reports NG. "In the U.S. alone, more than a hundred thousand people need heart transplants each year, but only about 2,000 receive one."
The move now is to artificially expand the organ supply using a variety of methods. Some scientists have attempted 3-D organ printing while others have pursued avenues like mechanical organs. Another option is the chimera, a hybrid of two species, to grow human organs organically. From National Geographic:
To make chimeras, researchers isolate one animal's stem cells, which can develop into any cell type in the body. They then inject some stem cells from one species into the embryo of another—a tricky procedure to get right.
If the embryo's DNA is hacked so that it does not grow a particular organ, the interloping cells would be the only ones that could fill in the gap. In this way, researchers could grow a human liver inside of a living pig, for example.
In 2017, researchers using this method successfully grew mouse pancreases in rats—and showed that transplants using the pancreas could cure diabetes in diabetic mice. The very next day, Salk Institute researchers announced that they could keep pig embryos injected with human stem cells alive for 28 days.
However, the human cell count in the pig equaled about one in a hundred thousand; far too low for an organ transplant. According to the American Association for the Advancement of Science, researcher Pablo Ross of the University of California, Davis, has boosted the human cell counts in sheep embryos to one in ten thousand.
“We think that that's still not probably enough to generate an organ,” Ross said during a press briefing.
One percent of the embryo would have to be human for the transplant to work. The challenge then is to protect against immune rejection, which would require leftover bits of animal viruses to be "struck from the pig or sheep's DNA."
Scientists cautioned against thinking that a real ManBearPig will be walking the Earth soon.
“The contribution of human cells so far is very small. It’s nothing like a pig with a human face or human brain,” said Stanford University researcher Hiro Nakauchi, Ross's collaborator.