In Nature Opinion Piece, Case Western Reserve Researcher Calls for Animal-Human Embryo Research to Proceed – but with Strong Animal Protections

In a World View opinion column published in Nature, a Case Western Reserve University School of Medicine researcher calls for animal-human embryo research to proceed – but only with strong animal protections in place. So-called “chimera” research raises the hope of producing human organs in genetically modified large animals, such as pigs and sheep, offering a potential solution to the persistent shortage of human organs for transplantation.

Insoo Hyun, PhD, associate professor of bioethics, urges such research to proceed only after “knowing the right and wrong ways to treat sentient beings according to complexities of their attributes.”

Hyun’s recommendations appear in the journal’s September 15th issue and come a week after the National Institutes of Health closed a month-long public comment period on proposed new regulations, widely expected to be adopted, that would lift a moratorium that currently forbids federal funding for chimera embryo research.

For decades, research has taken place on animal-human chimeras (after a Greek mythological figure with the head of a lion, the body of a goat, and the tail of a serpent), without much controversy in the United States, such as in the case of mice transplanted with human cancer cells. However, concerns have arisen about research using human pluripotent stem cells, the focus of the current NIH moratorium. These cells are made from skin or blood cells which are genetically modified to act like embryonic stem cells that can form any adult cell types including human organs.

Hyun’s recommendations come in response to concerns that the transfer of human stem cells into animal hosts would result in an animal with a human organ with at least partially human moral status, especially if the central nervous system is involved. He writes, however, that “The moral status of humans is not automatically assured by our genetic composition or the physical arrangement of our cells. Rather, it is sustained by a complex of mental traits …” which cannot develop in such chimeras.

He notes that chimera studies that involve sentient animals are already tightly regulated via the US Animal Welfare Act and other national and international research policies. He adds, however, that since “the transfer of human stem cells could produce unpredicted effects on the resulting chimeras’ equilibria and capacities for suffering, it is crucial that qualified veterinary staff and researchers monitor experiments” and if necessary, apply swift, humane care.

Under the NIH’s pending proposals, an internal steering committee would provide guidance on chimera research proposals, an approach consistent with new professional guidelines for stem cell research offered by the International Society for Stem Cell Research, which themselves are based on an advisory report which Hyun helped draft.

In addition to protecting animals, Hyun notes that “[g]rounding the ethics and regulation of human-animal chimera research in anything other than animal welfare would invite serious practical and philosophical difficulties.” He points out that for example, one argument used against transferring human stem cells into animal embryos is that this research is not overseen by animal research committees when it is limited to test-tube experiments. But, he says, the “challenge for these critics … is to explain why animal embryos containing human cells deserve serious consideration of their moral status – enough to potentially rule out their use – when standard human embryos can be used in other projects.”

The World View column in which Hyun’s piece appears is described by Nature as a "must-read weekly rapid response opinion column, which offers senior figures and commentators a platform to discuss events that affect the world’s scientific community.”


For more information about Case Western Reserve University School of Medicine, please visit:

Founded in 1843, Case Western Reserve University School of Medicine is the largest medical research institution in Ohio and is among the nation's top medical schools for research funding from the National Institutes of Health. The School of Medicine is recognized throughout the international medical community for outstanding achievements in teaching. The School's innovative and pioneering Western Reserve2 curriculum interweaves four themes--research and scholarship, clinical mastery, leadership, and civic professionalism--to prepare students for the practice of evidence-based medicine in the rapidly changing health care environment of the 21st century. Nine Nobel Laureates have been affiliated with the School of Medicine.

Annually, the School of Medicine trains more than 800 MD and MD/PhD students and ranks in the top 25 among U.S. research-oriented medical schools as designated by U.S. News & World Report's "Guide to Graduate Education."

The School of Medicine is affiliated with University Hospitals Cleveland Medical Center, MetroHealth Medical Center, the Louis Stokes Cleveland Department of Veterans Affairs Medical Center, and the Cleveland Clinic, with which it established the Cleveland Clinic Lerner College of Medicine of Case Western Reserve University in 2002.

Media Contact(s):

Marc Kaplan
Associate Dean, Marketing and Communications
The School of Medicine
Case Western Reserve University
Office: 216-368-4692