Mice Get Human Brain Cells in Study

By PAUL ELIAS

Mice get human brain cells in study

SAN FRANCISCO Add another creation to the strange scientific menagerie where animal species are being mixed together in ever more- exotic combinations.

Scientists announced Monday that they had created mice with small amounts of human brain cells in an effort to make realistic models of neurological disorders such as Parkinsons disease.

Led by Fred Gage of the Salk Institute in San Diego, the researchers created the mice by injecting about 100,000 human embryonic stem cells per mouse into the brains of 14-day-old rodent fetuses.

Those mice were each born with about 0.1 percent of human cells in each of their heads, a trace amount that doesnt remotely come close to humanizing the rodents.

This illustrate that injecting human stem cells into mouse brains doesnt restructure the brain, Gage said.

Still, the work adds to the growing ethical concerns of mixing human and animal cells when it comes to stem-cell and cloning research. After all, mice are 97.5 percent genetically identical to humans.

The worry is if you humanize them too much, you cross certain boundaries, said David Magnus, director of the Stanford Medical Center for Biomedical Ethics. But I dont think this research comes even close to that.

Researchers are nevertheless beginning to bump up against what bioethicists call the yuck factor.

Three top cloning researchers, for instance, have applied for a patent that contemplates fusing a complete set of human DNA into animal eggs in order to manufacture human embryonic stem cells.

One of the patent applicants, Jose Cibelli, first attempted such an experiment in 1998 when he fused cells from his cheek into cow eggs.

The idea is to hijack the machinery of the egg, said Cibelli, whose current work at Michigan State University does not involve human material because that would violate state law.

Researchers argue that co-mingling human and animal tissue is vital to ensuring that experimental drugs and new tissue replacement therapies are safe for people.

Others have performed similar experiments with rabbit and chicken eggs while University of California-Irvine researchers have reported making paralyzed rodents walk after injecting them with human nerve cells.

Doctors have transplanted pig valves into human hearts for years, and scientists have injected human cells into lab animals for even longer. But the brain poses an additional level of concern because some envision nightmare scenarios in which a human mind might be trapped in an animal head.

Human diseases, such as Parkinsons disease, might be amenable to stem-cell therapy, and it is conceivable, although unlikely, that an animals cognitive abilities could also be affected by such therapy, a report issued in April by the influential National Academies of Science that sought to draw some ethical research boundaries.

The report recommended that such work be allowed, but with strict ethical guidelines established. Protocols should be reviewed to ensure that they take into account those sorts of possibilities and that they include ethically sensitive plans to manage them if they arise, the report said.

At the same time, the report did endorse research that co- mingles human and animal tissue as vital to ensuring that experimental drugs and new tissue replacement therapies are safe for people.

Gage said the work published Monday in the journal Proceedings of the National Academy of Sciences is another step in overcoming one of the biggest technical hurdles confronting stem-cell researchers: when exactly to inject the cells into patients.