Transgenic Mice: Human, All Too Human?

Posted by Marcy Darnovsky June 3, 2009
Biopolitical Times
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A German research team reported last week that they have created "humanized" mice by transferring a human version of a language gene into their brains. The researchers found that the swap produces measurable neurological differences.

The most dramatic of the changes is in the transgenic mice's brains: Nerve cells in the basal ganglia, a region which in humans is involved in language production, are structurally more complex. The humanized mice, which the researchers say are healthy, also make ultrasonic whistles that are lower in pitch, and display "decreased exploratory behavior."

The lead author told the New York Times that "putting significant human genes into mice is the only feasible way of exploring the essential differences between people and chimps, our closest living relatives." This, he says, is because there "is no good way of genetically engineering chimps, even it were ethically acceptable."

There are now many animals in research laboratories whose bodies contain human genes or tissues. Some, like these humanized mice, are transgenics - the products of gene transfer. Others, called chimeras, are created by adding human stem cells to an animal, or an animal embryo.

One of the fraught ethical questions they raise is how human a humanized animal must be before we begin to worry. What if our experimental creatures begin to display some degree of human consciousness? And once we're worried, what do we do?

The stem cell research guidelines issued by the National Academies of Sciences in 2005 concurred that the "idea that human neuronal cells might participate in 'higher order' brain functions in a nonhuman animal, however unlikely that may be, raises concerns that need to be considered" and recommended a prohibition on mixing human stem cells with embryos from monkeys and other primates. The guidelines also advised that research protocols ask (and presumably answer) the question:
If visible human-like characteristics might arise, have all those involved in these experiments, including animal care staff, been informed and educated about this?

Stanford University law professor and bioethicist Henry Greely, who has studied proposals by his Stanford colleague Irving Weissman to create human-mouse chimeras, believes "there is a nontrivial risk of conferring some significant aspects of humanity" on the animals. In 2005, Weissman got a go-ahead from Greely's ethics committee to create mice with "a significant number of human brain cells" by transplanting human neurons.

He had also asked the committee for an opinion about a "thought experiment" - about the ethics of making chimeric mice with brains that are a hundred percent human. As long as the mice's brains continued to look mouse-like, he told the Washington Post, they could be used for research.

But if there were any sign that they were taking on a "distinctly human architecture," he said, they could be killed.

Previously on Biopolitical Times: