A petri dish containing embryonic human stem cells. Image : AP

An international collaboration is claiming to have created hybridized human-monkey embryos in China. Disturbingly, the research could result in monkeys capable of producing human organs for transplants, leading to a host of ethical concerns.




A researcher involved in the experiment, biologist Estrella Núñez from the Catholic University of Murcia (UCAM), confirmed the achievement to Spanish news site El País. The project is being led by Juan Carlos Izpisúa Belmonte, who runs a lab at the Salk Institute in the United States.

Few details are known, but the experiment, in which the researchers created chimeric, or hybridized, human-monkey embryos using human stem cells, is “an important step towards [Izpisúa Belmonte’s] final goal of converting animals of other species into factories of organs for transplants,” reports El País. All hybridized embryos were destroyed after 14 days, and no monkey was produced during the experiment.


Regrettably, Núñez leaked these details to El País prior to the publication of a formal study. That said, she described the results as “very promising,” and said the paper is currently pending peer review in a “prestigious international scientific journal,” reported El País.

Previously, Izpisúa Belmonte tried to grow pig embryos using human stem cells, but these cells failed to sufficiently take hold after the hybridized pig fetuses were implanted into sows. The purpose of this experiment was to test the viability of using pigs to grow human organs for transplants. The shortcomings of this experiment, however, may have led Izpisúa Belmonte to his alleged experiments on monkeys—and by consequence, to an undisclosed laboratory in China.



Indeed, as to why the experiments were conducted in China, and not in Spain or the United States, remains an open question, but it may have to do with lax Chinese laws involving transgenic research. In the United States, for example, federal funds cannot be used to create human-animal chimeras, that is, organisms in which human and animal characteristics have been combined. As we reported earlier this week, Japan became the first country to approve the creation of animal embryos with human cells and then bring them to term. Work on human-animal chimeras was sanctioned in Spain two years ago, but the UCAM researchers went to China owing to the lack of suitable infrastructure in Spain, Núñez told El País.


Here’s how the researchers created the chimeric human-monkey embryos, as El País reported: First, the researchers created genetically modified monkey embryos in which the genes responsible for the normal formation of organs were disabled. Human embryonic stem cells were then injected into these monkey embryos. Stem cells are special in that they’re capable of becoming virtually any other type of cell in the body. In this case, the researchers were hoping to see the human stem cells take over in terms of the monkey’s organ development. As noted, the embryos were apparently destroyed after 14 days in accordance with standard experimental guidelines.

The supposed point of this research is to eventually bioengineer monkeys such that they’re capable of producing organs, like kidneys or livers, comprised of human cells, which could then be harvested and used for transplants. Human-monkey chimeras with human organs could also be used in studies to test the effectiveness and safety of new drugs or other medical interventions. Or as University of California, Davis veterinary researcher Pablo Ross told MIT Technology Review, hybridized monkey embryos could be used to explore “questions of evolutionary distance and interspecies barriers.”


Unrelated research done on monkeys has resulted in “humanized” monkeys with autism, and cloned monkeys engineered to have predispositions to anxiety, depression, and even schizophrenia-like behaviors. Monkeys are considered ideal experimental models on account of their similarity to humans, both physically and cognitively, and because research on apes is progressively being phased out. Unfortunately, however, the desired similarities shared among humans and other primates raises important ethical questions in regards to animal suffering.

Speaking to Gizmodo, bioethicist Arthur Caplan from NYU Langone Health expressed his concerns about the research reported in El País.


The intermingling of human and animal traits triggers ethical weariness, especially in the United States, he said, and people “get frightened if you make a primate too human-like, whether it’s in the brain or in its physical appearance.” Caplan said we won’t be ready for this type of research until international agreements addressing protocols and purpose are established. Until then, work on human-animal chimeras “is premature,” he said.

Also, the proposed use of monkeys to produce human organs didn’t make a lot of sense to Caplan, as monkey organs “are too small, except maybe for children,” he said. “That’s why we went to pigs in the first place.”


“Press leaks are not the way to do science.”

Caplan also expressed concerns about how the scientists chose to disclose their findings.


“Press leaks are not the way to do science,” Caplan told Gizmodo. The El País report reminded Caplan of the research done by discredited Chinese geneticist He Jiankui, who clandestinely used the CRISPR-cas9 gene-editing tool to create genetically modified human babies. What’s required for this type of controversial—but important—research is “transparency, openness, disclosure of protocols, and disclosure of purpose right from the start,” he said. “Who reviewed this experiment? Who approved it? Who’s funding it? All of this needs to be disclosed up front.”

Failure to do so, said Caplan, leads to speculation, which in turn breeds fear. The Salk Institute, UCAM, and the contributing Chinese institute should disclose what they know about the experiment instead of staying silent, he said. On that note, we contacted Izpisúa Belmonte and the Salk Institute to confirm the El País report, but we didn’t hear back from either party by the time of publication .


Letitia Meynell, an associate professor at Dalhousie University, said it’s “really depressing to see the willingness of scientists to engage in research tourism when the ethical standards of their home country make it impossible to conduct that research there,” she told Gizmodo. “Certainly, these are ethically controversial issues. However, scientists who are willing to flout the ethics of their home countries and institutions should see themselves as obligated to make the ethical case for what they are doing,” she said.

The surprise media disclosure also has Caplan questioning the researchers’ motives.


“It makes me wonder if they’re trying to make some sort of intellectual claim rather than move the science along, or they’re trying to be the first, generate hype, or somehow attract more money,” he said, saying the chosen approach “sheds all sorts of bad light where their might be clarity.”

T he lack of global ethical standards has University of Toronto bioethicist Kerry Bowman worried about the future.


“This research shows disregard for a sentient social species,” Bowman told Gizmodo. “Although research to date has had a ‘red line’ in terms of the length of gestation allowed to progress [i.e. the 14 days limit], this will eventually be lifted. What is the moral status of any creature with elements of human biology?”

No doubt, the prospect of human-animal chimeras introduces serious ethical concerns—but also the potential for tremendous medical gain.


Eventually, transgenic biotechnologies could be used to treat a host of medical problems, ranging from genetic disorders to immunities that combat infectious diseases. It could even be used to introduce new traits altogether. To get there, however, we need to tread carefully and safely, and not at the expense of excessive animal suffering. Sadly, this research team led by Izpisúa Belmonte has started off on the wrong foot.