Friday, January 8, 2016

Human-Animal Chimeras Are Gestating on U.S. Research Farms

Braving a funding ban put in place by America’s top health agency, some U.S. research centers are moving ahead with attempts to grow human tissue inside pigs and sheep with the goal of creating hearts, livers, or other organs needed for transplants.

The effort to incubate organs in farm animals is ethically charged because it involves adding human cells to animal embryos in ways that could blur the line between species.

Last September, in a reversal of earlier policy, the National Institutes of Health announced it would not support studies involving such “human-animal chimeras” until it had reviewed the scientific and social implications more closely.

The agency, in a statement, said it was worried about the chance that animals’ “cognitive state” could be altered if they ended up with human brain cells.

The NIH action was triggered after it learned that scientists had begun such experiments with support from other funding sources, including from California’s state stem-cell agency. The human-animal mixtures are being created by injecting human stem cells into days-old animal embryos, then gestating these in female livestock. (...)

The experiments rely on a cutting-edge fusion of technologies, including recent breakthroughs in stem-cell biology and gene-editing techniques. 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.

Because chimeras could provide a new supply of organs for needy patients and also lead to basic discoveries, researchers including Garry say they intend to press forward despite the NIH position. In November, he was one of 11 authors who published a letter criticizing the agency for creating “a threat to progress” that “casts a shadow of negativity” on their work.

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.”

Hiromitsu Nakauchi, a stem-cell biologist at Stanford University, began trying to make human-sheep chimeras this year. He says that so far the contribution by human cells to the animals’ bodies appears to be relatively small. “If the extent of human cells is 0.5 percent, it’s very unlikely to get thinking pigs or standing sheep,” he says. “But if it’s large, like 40 percent, then we’d have to do something about that.”

by Antonio Regalado, MIT Technology Review | Read more:
Image: Ping Zhu