Should the U.S. government use tax dollars to fund scientists fusing human stem cells into early animal embryos in order to create “chimeras” that are part human and part pig? Or part mouse?
The U.S. National Institutes of Health says the answer is yes. The agency announced Thursday that it plans to lift a moratorium that since last year has blocked taxpayers’ money from flowing to this type of hot-button research.
Carrie Wolinetz, the NIH’s associate director for policy, said experiments to inject human stem cells into early-stage animal embryos “are really important and exciting to understand how disease works” and to explore new medical treatments.
At the same time, the agency is proposing stricter controls on certain experiments most likely to lead to monkey-men or other bad science fiction.
Last September, the NIH surprised the scientific community by slapping a broad moratorium on funding of any research in which human stem cells are injected into animal embryos. By then, the agency knew what MIT Technology Review reported exclusively in January, which is that such experiments were already under way in the U.S., with several dozen sows and sheep carrying fetuses potentially containing a mix of human cells.
At the time, none of the animals had been brought to term, out of scientific caution. Scientists carrying out that work at the Salk Institute and at Stanford University say the fetal animals would only contain, at the most, a small proportion of human cells.
However, Rudolf Jaenisch, a biologist at MIT, says that to his knowledge, none of these experiments have worked. That is, no human cells actually survived to contribute to the animals’ bodies. “I don’t think these chimeras have worked at all at this point,” he said. “But it’s a very important experiment.”
Human-animal mixtures aren’t new. Wolinetz noted in a statement that biomedical researchers “have created and used animal models containing human cells for decades” to gain insights into biology and disease. Scientists often grow human tumors inside of mice, for example.
But the new research is different, because potent human stem cells are being injected directly into a very early-stage animal embryo, consisting of just a couple of dozen cells. Theoretically, the human cells could then end up contributing to any part of the animal, and in any amount.
“There is definitely interest in the scientific community to pursue these studies,” says Arun Sharma, a researcher at Stanford University. “In my opinion, the NIH is doing the right thing in thoroughly evaluating the scientific and bioethical implications of this work before pushing forward.”
What’s the point of such experiments? One is that it might be possible to create an otherwise normal pig whose entire heart—or whole liver—is made from human cells. That would create a new way to farm human organs for transplant.
“What is new is as the science has progressed, as we have seen advances in stem-cell technology and gene-editing capabilities, we’ve begun to creep a little bit closer to the science leading to some of these ethical concerns,” says Wolinetz.
The issue was clearly a delicate one for the NIH, which was caught between advancing science and a possible political bombshell that could lead to public backlash. The agency said it would form a special committee to oversee funding of these human-animal mixtures—a move that could raise questions over political interference in science.
But the agency also tried to firm up restrictions on the scariest possibilities. It said it wants to expand an existing regulation that forbids funding any research combining human cells with early embryos of apes or monkeys. The species are just too close, and the results too disturbing to contemplate.
The agency also wants to explicitly bar any of these human-animal chimeras from being allowed to reproduce. The risk—very remote but which could have disastrous consequences for public confidence in science—is if two chimeras mated and gave rise to a human fetus. That could happen if their sperm or egg were human.
(Read more: “Human Animal Chimeras Are Gestating on U.S. Research Farms”)