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Chimeras a myth no more
Ethical concerns arise as scientists add human brain cells to other creatures


Scala / Art Resource, N.Y.
Chimera. Fifth century BCE, Etruscan. Museo Archeologico, Florence, Italy   (Scala / Art Resource, N.Y.)
They look like mice, yet they have some human neural cells working in their brains.  When researchers at Stanford University recently inserted human embryonic stem cells into the brains of fetal mice, these cells were found to have transformed into functional human brain cells when these mice were born.  The human brain cells had migrated to various regions of the mouse brain, where they integrated with the cells living there.

Might such experiments result in the creation of mice with human brains? If so, would these mice start thinking and acting like human beings? Is it wrong to create such human-nonhuman chimeras?

This experiment was the latest in the ethically challenging area of human-animal “chimera” research.  The chimera was a fire-breathing monster found in Greek mythology with the head of a lion, the body of a goat and the tail of a serpent.  It was taken as a sign that some terrible disorder pervaded the universe and threatens humankind.

Today, scientists, borrowing from Greek mythology, refer to any being with cells of two different kinds of creatures as a “chimera.”  However, they see the human-nonhuman chimeras created in stem-cell research as signs of hope, rather than chaos, for they offer the possibility of developing treatments for serious neurological diseases.  Scientists say that it is essential to commingle human stem cells with living animal tissue to ensure the safety of stem-cell replacement therapies.  Before we try transferring human stem cells to human beings, we must have reliable evidence that this can be done in nonhumans without damaging consequences. 

Human-nonhuman chimera experiments have been carried out for several decades without creating public concern.  A United States senator received a pig-heart-valve transplant to restore his heart function, and human blood and skin stem cells have been inserted into living mice to learn how they grow and develop.  So it is not the mixing of human and animal materials in itself that raises ethical qualms. 
It is the insertion of certain kinds of human cells -- brain or reproductive cells -- into animals that creates ethical concerns.

People fear that a human mind might be trapped inside an animal’s body when human embryonic stem cells are transferred to the brains of mice or that a human being will result from the mating of animals if human embryonic stem cells were to affect the germ cells of animal embryos, causing them to develop human sperm and eggs.  Recognizing these untoward possibilities, the National Academy of Sciences has developed guidelines on chimera research that would prevent them.

For Christians, the complete fusion of animals and humans would run counter to the sacredness of human life and to recognition that humankind is created in the image of God.  Yet in the Stanford experiment, the human cells had no apparent impact on the behavior of the resulting mice and did not open the door to the creation of a “hum-mouse.” Although about 100,000 embryonic stem cells were injected into the mice, only about 100 of them survived and were integrated into the mouse brains.

Thus, the brains of these mice were still more than 99 percent mouse.  Further, the human cells seemed to be hitchhiking along with the mouse cells and responding to cues in a similar way. They became more mouse-like. This suggested that these rodents were highly unlikely to function like human beings but would remain mice that had a few human cells in their brains.

Indeed, it would seem impossible for a mouse that had received human embryonic or differentiated neural cells to develop a human brain because the mouse skull is too small to house a human brain.  Moreover, evidence from earlier chimera experiments, as from this study, indicates that the mouse brain controls the development of human cells inserted into it.  Therefore, it is extremely unlikely that God’s plan for humankind would be radically changed by these experiments and that a full-fledged human-nonhuman chimera would emerge.

This sort of chimera research provides encouragement for those who hope that one day stem-cell-based therapies will be developed for diseases as Parkinson’s, Alzheimer’s and Lou Gehrig’s.  However, these embryonic stem cells must be derived from “spare” human embryos remaining at IVF clinics that cannot be used for reproductive purposes.

This raises concerns for those Christians who view these embryos as living human beings.  To address their objections, scientists are seeking alternative ways of developing embryonic stem cells.  Meanwhile, they are proceeding with the use of excess human embryos donated for research by couples, rather than letting them waste away, and hoping that they can help to overcome serious diseases that have long plagued humankind.

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