In a chilling experiment seemingly out of science fiction, scientists created two human-pig embryos — then destroyed them after a few weeks of growth.
The creations included human stem cells grown inside pig embryos, with the cells constituting only a small part of the embryos. The scientists’ hope is that such recombinations could be used to grow replacement organs for humans that wouldn’t be rejected by the recipient’s body.
The controversial experiment was conducted in California and Spain, and paid for by private foundations. The U.S. suspended taxpayer funding for such animal-human combinations in 2015.
The possibility of growing human organs in pig embryos is still “far away,” researcher Juan Carlos Izpisua Belmonte of the Salk Institute in California said of the experiment in the journal Cell, in an article published Thursday. He called the work “just a very early step toward the goal.”
Such work presents incredible challenges.
“Species evolve independently, and many factors dictating the developmental programs might have diverged, which makes it difficult to blend cells from one species to a developing embryo from another,” Dr. Jun Wu told CNN. “The larger the evolutionary distance, the more difficult for them to mix.”
Animals with cells from different species are called chimeras. Such combinations had been successfully created earlier with mice and rats, but larger animals like pigs would be needed to make human-sized organs. That could help ease the shortage of human donors for transplants. A sick person is added every 10 minutes somewhere in the world to a waiting list for an organ, and each day 22 people on the list die for lack of an organ, according to statistics.
The Salk team is working on making human-friendly pancreases, hearts and livers in pigs. The animals would grow the organs in place of their own, and then would be euthanized before the organ is removed.
The vision raises huge ethical concerns, such as fears about an animal developing some human-like characteristics.
As Isoo Hyun, an associate professor of bioethics and philosophy at Case Western Reserve University, explained to CNN: “If you up the biological contribution of the human stem cells, are you also somehow turning them morally into a human-like thing with human rights?”