An intense debate has flared over whether the federal government should fund research that creates partly human creatures using human stem cells.

The National Institutes of Health declared a moratorium in late September on funding this kind of research. NIH officials said they needed to assess the science and to evaluate the ethical and moral questions it raises. As part of that assessment, the NIH is holding a daylong workshop Friday.

Meanwhile, some prominent scientists worry that the NIH moratorium is hindering a highly promising field of research at a crucial moment. Such concerns prompted several researchers this week, writing in the journal Science, to call on the NIH to lift the moratorium.

“The shadow of negativity cast around this research is going to have a major negative impact on any progress going forward,” says Sean Wu, a cardiologist and assistant professor of medicine at Stanford University, who helped write the article.

The moratorium was prompted by an increasing number of requests to fund these experiments, says Carrie Wolinetz, the NIH’s associate director for science policy. In the experiments, scientists propose to insert human stem cells into very early embryos from other animals, creating dual-species chimeras.

“The science is knocking at our door,” Wolinetz told Shots in advance of the workshop. She says NIH wants to “make sure that we are fully prepared from a policy and guidance point of view” before making decisions about such grants.

Scientists have been creating partly human chimeras for years. Researchers use rats with human tumors to study cancer, for example, and mice with human immune systems to do AIDS research.

What’s new is putting human stem cells into the embryos of other animals, very early in embryonic development.

“The special issue here with stem cells is that those types of human cells are so powerful and so elastic that there’s great worry about the degree to which the animals could become humanized,” says Insoo Hyun, a bioethicist at Case Western Reserve University.

The goal of the research is to create chimeras that lead to new treatments for human diseases. For example, the technique might enable scientists to create better animal models for studying diseases in the laboratory.

Researchers also hope to grow human organs in animals that would be closely matched to patients needing transplants.

“This could have a big impact in the way medicine is practiced,” says Juan Carlos Izpisua Belmonte, a professor of gene expression at the Salk Institute for Biological Studies.

“We don’t have enough organs for transplantation,” Belmonte says. “Every 30 seconds of every day that passes, there is a person that dies that could be cured by using tissues or organs for transplantation.”

He tells Shots he thought he was on the verge of getting an NIH grant to pursue this research before the moratorium was imposed.

The prospect of inserting human cells into early animal embryos raises a variety of concerns.

Françoise Baylis, a bioethicist at Dalhousie University in Nova Scotia, Canada, says the engineering of creatures that are partly human and partly nonhuman animal is objectionable because the existence of such beings “would introduce inexorable moral confusion in our existing relationships with nonhuman animals, and in our future relationships with part-human hybrids and chimeras.”

Another concern is that the human cells could end up in the brains of the animals. That raises the prospect that “this will somehow give the animal a human consciousness, human mental capabilities,” says Hank Greely, a bioethicist at Stanford University.

In addition, some scientists and bioethicists fear the stem cells could create human eggs and sperm in the animals.

“If you had a male mouse that had human sperm in it, that’s going to be a concern to some people, especially if it’s anywhere near a female mouse that has human eggs in it,” Greely says. “To say the least, it’s disconcerting to think about two mice making a human embryo.”

Still, Greely, Hyun and the scientists conducting the research all agree that the most alarming concerns are highly unlikely. And, they say, safeguards could be put in place to allow the research to go forward.

For example, scientists could engineer the cells so that they were unable to form human brain cells, sperm or eggs. The animals could also be isolated or sterilized to prevent them from breeding.

“There are certainly very effective strategies that would alleviate the concerns,” Wu says.

Copyright 2015 NPR. To see more, visit http://www.npr.org/.

Transcript :

RENEE MONTAGNE, HOST:

Now we turn to something that hereto for has been fantastical, chimeras, creatures that are part human, part animal. And there’s a big debate now on how far scientists should go turning the fantastical into the real. Today, the National Institutes of Health will be hearing from scientists who want funding for research that would create chimeras using human cells. NPR’s Rob Stein joins us to explain what this is all about. Good morning.

ROB STEIN, BYLINE: Good morning, Renee.

MONTAGNE: OK, we’re going to start with what exactly is a chimera.

STEIN: Well, the term chimera comes from Greek mythology, actually. There was this fire-breathing monster with the head of a lion, the body of a goat, and the tale of a serpent. But it – when it to comes medical research, what they’re really talking about are animals that have been changed in some way to include either human cells or human structures. They’ve done things like create rats with tumors to study human cancer, and they’ve created mice with human immune systems.

MONTAGNE: Right, all of this in the service of medical research, so what’s new and stirring up controversy now?

STEIN: So what’s new are human stem cells. And as you know, stem cells can turn into pretty much any kind of tissue or cell in the body, and that’s what makes them so versatile. And in this case, what scientists want to do is put stem cells into very early embryos of different animals to see if they can create a whole new type of chimera. And they want to do this for several reasons. One thing they’d like to do is create better animal models of human diseases that they could study in the laboratory and hopefully come up with new treatments. Another thing they think they could do is use sheep or pigs that would have fully human organs that they could use for transplantation, like kidneys or pancreases for people with diabetes.

MONTAGNE: Well, then nobody is talking about, say, a lion’s body with a human face. But is that the sort of thing people are worried about?

STEIN: What they’re worried about is that the fact that these stem cells are so versatile they can turn into, as I said, any kind of tissue or cell in the body, if you put them into very early embryos, who knows what they’ll end up becoming? They could end up, for example, becoming human brain cells in these animals, and obviously, that starts to raise all kinds of ethical and moral questions. Will these animals have some sort of semblance of consciousness or human thinking abilities? And that starts to blur the line of what the moral status of these animals are. Another concern is they could turn into human sperm and human eggs. And so what would happen if two animals that you did this to ended up breeding? Could you end up with some sort of hybrid animal human offspring or human embryo?

MONTAGNE: Well, if any of these are remotely possible, then clearly, there’s a reason to be concerned here. But what are scientists saying about this?

STEIN: Well, what the scientists are telling me is that those kinds of scenarios I just described are extremely unlikely, if not impossible. But just to be on the safe size, there are things they could do to make sure it didn’t happen. Like, for example, they could engineer the stem cells so that they could not become human brain cells or could not become human sperm or eggs. Another thing they could do is even sterilize them to make sure that there was no possibility they could ever breed.

MONTAGNE: And here’s where the NIH gets into it, the National Institutes of Health. What is it doing?

STEIN: So what happened is a couple months ago, the National Institutes of Health announced that it was issuing a moratorium on funding any kind of research in this area. The NIH is gathering all the top researchers and the top bioethicists in this field together today to really hash all this out. And I spoke to several of the scientists in the field, and they’re pretty upset about the moratorium because they think it’s really holding things up, and this is a very promising field. Now the bioethicist I talked to said that, but there are these concerns that it’s really important that we talk about it. And in fact, one of the bioethicists I talked to said, look, that myth, that chimera myth I mentioned at the beginning, it’s often held up as a warning to scientists about the dangers of chimeras. If you really work closely, the myth, really, is warning against hubris. You have to act responsibly and be careful when you’re tinkering with nature like this.

MONTAGNE: All right, well, thank you, NPR’s Rob Stein.

STEIN: Sure, nice to be here. Transcript provided by NPR, Copyright NPR.