Courtesy Understanding Animal Research/
Technology / Experimental Medicine

The Ethical Conundrum of Chimeras

The medical community is constantly on the lookout for innovative solutions to humanity’s ailments, and thanks to advances in science and technology, cures for diseases and disorders once considered incurable are always around the corner. One development is the human–animal hybrid. These artificial hybrids, called chimeras, have the potential to create better model organisms to study human disease.

So far, chimera experimentation is entirely non-human, focusing particularly on common lab animals, but results are promising. One study found that diabetic mice could be cured using islets (clusters of insulin-producing cells) grown in mice–rat chimeras. Applying this therapy to humans would provide a cure to the 415 million people with diabetes worldwide. If successful, this approach could be used to treat many other diseases.

To create a hybrid, researchers first delete from the host embryo’s genome the gene for the desired organ. Researchers inject human-induced pluripotent stem cells—adult human cells that have been reprogrammed into embryonic stem cells and are able to develop into any type of cell—into the embryo, which researchers place into the womb of an adult organism. When the organs have begun to form in the embryo, they remove the chimera. An organ grown in the chimera, once developed, is useful for study and experimentation. Some scientists hope to push the usefulness of chimeric organs even further, and urge that their implantation in human patients be considered in order to reduce waiting times for human donors.

But chimeras, like many other great scientific and medical advances, come with both ethical and practicals questions. Scientists cannot predict with certainty whether the introduction of the hybrid organs will affect other parts of the host. Some people, like Stuart Newman, professor of cell biology at New York Medical School, have expressed concern that the stem cells enter the host embryo’s brain, causing these animals to develop human consciousness or human needs. Others worry that the chimeras will develop human sperm and eggs, which might allow the possibility of a human or chimeric fetus growing. Many are concerned that working toward the goal of creating chimeras goes beyond what humans should ethically try to accomplish. Newman believes that chimeras are “getting into unsettling ground that…is damaging to our sense of humanity.”

Despite growing apprehension, the National Institute of Health called a moratorium on funding for all chimera research. This has hindered chimera research and delays the revolutionary scientific discoveries that this model could make possible.

Scientific research often takes us into unknown territory. As a society, we must work to resolve ethical issues quickly as they arise from constantly progressing research. We must weigh the advantages and pitfalls of increased scientific and medical knowledge and the potential unintended consequences of overstepping ethical boundaries, while making minimal sacrifices to the welfare of the such advances could benefit.