Human-animal hybrid research raises hopes and concerns

·Senior Editor
·6 min read

“The 360” shows you diverse perspectives on the day’s top stories and debates.

What’s happening

Scientists have successfully grown embryos that contain a combination of human and monkey cells, a major breakthrough in a rapidly advancing field of genetics that researchers say could one day revolutionize our understanding of human development.

An international team of scientists led by Juan Carlos Izpisua Belmonte from the Salk Institute in La Jolla, Calif., injected human stem cells into monkey embryos and observed as the two different sets of cells developed together. None of the embryos survived longer than 19 days, but experts say the experiment still represents a significant step forward in the science of cross-species hybrids — known as chimeras.

The same scientists had successfully produced pig and sheep embryos with human cells, but started experimenting with primates after only a tiny percentage of the cells in those tests survived. The researchers hope that someday in the near future fully developed human-animal chimeras might provide insights into the earliest stages of human development, increase understanding of how certain diseases can be treated and even provide organs for human transplants.

The science of combining genes from two animals dates back to the 1970s. But new technologies have led to a series of breakthroughs in recent years. For all its potential promise, chimera research is also controversial. Many countries, including the U.S., have at times restricted experiments on nonhuman embryos containing human cells. The National Institutes of Health, a government agency that is the biggest source of biomedical research funding in the U.S., has banned the use of federal dollars for human-animal chimera studies.

Why there’s debate

For all their promise, hybrid embryos raise ethical issues that have led many experts in the field to argue against further research. One prominent bioethicist said these experiments, even in their early stages, “open Pandora’s box” to a future where living human-nonhuman hybrid animals can be raised to full maturity. That situation, they argue, raises questions of just how much human material a monkey can have before it is itself effectively human.

There are also concerns about how much control can be exerted over which parts of the body contain human cells. A chimera with human genetic material in its liver, for example, is a lot less worrisome than one with human DNA in its brain or reproductive cells. There are also, of course, animal-rights activists who oppose all scientific testing on animals.

The scientists who created the monkey-human embryos acknowledge these dilemmas and consulted several bioethicists while developing their research. In their eyes, the potential benefits chimeras could provide make further study worthwhile. They say hybrid embryos can be used in experiments that can be done on humans for legal and moral reasons. This freedom could provide insights that transform the way we understand the earliest stages of human development and unveil new treatments for chronic diseases, Belmonte said. He added that organ donations from chimeras could prevent thousands of people every year in the U.S. alone from dying while on transplant wait-lists.

What’s next

Hybrid embryo research still has a long way to go before any of the thornier ethical questions are tested in the real world. Next month, the International Society for Stem Cell Research is expected to release updated guidelines that could set new standards for what kinds of human-animal hybrid research is acceptable. The NIH says it’s waiting for these new rules before deciding whether it might lift its ban on funding for chimera research in the U.S.


Hybrid embryo research could save countless lives

“Such research should always be done cautiously, and be properly monitored. But it should also be encouraged, because the rewards it brings could turn out to be significant. Chimeric embryos may offer a way around ethical problems that make experiments on human embryos difficult. That could lead to new treatments for congenital diseases. … Easing the long-standing worldwide shortage of transplantable organs could save many lives.” — Economist

Chimera research creates too many troubling unknowns

“This work cuts across crucial moral boundaries. These human-monkey cells would not have just been bone or kidney tissue, but also brain neurons. Moreover, we are not talking mice or rats but monkeys, which have a much closer genetic affinity with humans. What might result from such a combining? I don’t think we should find out.” — Wesley J. Smith, National Review

It may be impossible to know where the line between human and animal really stops

“Extending the concept to our own species challenges the idea of human exceptionalism. What moral status might any such creature have? Would its human cells have any influence on the animal’s brain development and consciousness? How could we know?” — Oliver Duff, iNews

We shouldn’t let fear derail important research at such an early stage

“At the time of the first airplane, all the potential applications existed only in the minds of a few people. If the society were to decide that it was a horrible idea for humans to fly, we would miss a lot of things that turn out to be wonderful for everyone. A society that sees the world as what it is, not what it should be, is an effective society that can move forward.” — Human-animal embryo researcher Jian Feng to CNN

It matters a lot which parts of the animal have human cells

“A liver is kind of a liver, it doesn’t seem to have too many special properties, but the sperm and the egg and the brain, those are part and parcel of a person. So it feels much more ethically concerning to grow a person in a pig, as opposed to growing just some constituent part of a person. Someone has a heart transplant or a liver transplant, and it just kind of seems to make more sense.” — Neuroscience researcher Francis Shen to the Scientist

At its current stage of progress, chimera research is well within ethical bounds

“I don’t think it is particularly concerning in terms of the ethics, because you are not taking them far enough to have a nervous system or develop in any way — it’s just really a ball of cells. … [But] if you allow these animals to go all the way through and be born, if you have a big contribution to the central nervous system from the human cells, then that obviously becomes a concern.” — Developmental biologist Robin Lovell-Badge to the Guardian

Chimeras make the issues with typical animal testing even more extreme

“These concerns about chimeric research add to the already potent ethical issues associated with mainstream invasive animal research. Tens of millions of animals are sickened, injured, genetically manipulated, and killed in biomedical labs every year. … Chimeric research will only worsen the suffering of animals and move it into areas of unforeseen consequences, for which we are totally unprepared.” — Lori Marino, Stat

It’s good to debate the issue now, while the research is still in its infancy

“I don't think we’re on the edge of beyond the ‘Planet of the Apes.’ I think rogue scientists are few and far between. But they're not zero. So I do think it’s an appropriate time for us to start thinking about, ‘Should we ever let these go beyond a petri dish?’” — Bioethicist Hank Greely to NPR

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