Human Cells + Animal Cells = ?

Scientists Are Trying New Combinations In The Name Of Research

(AP)  United Kingdom researchers led by Dolly the Sheep creator Ian Wilmut are planning similar experiments, which aim to copy a Chinese research team's success with goats, reported in the journal Cell Research in 2003.

"The concerns about chimeras and mixing species may be justified in some circumstances," Yale researcher Gene Redmond said by e-mail from his St. Kitts laboratory, where he's studying Parkinson's disease by injecting human brain cells into monkeys. "But there are strong scientific reasons to do it in many cases and great benefits to be had for humanity."

Redmond's work is funded by the U.S. government, but he works in St. Kitts because it and the neighboring island of Nevis have a large population of feral African monkeys. The research aims to reverse the symptoms of Parkinson's by supplying dopamine, a chemical in the brain whose absence is thought to cause the disease.

"There seems to be little or no chance that the monkeys would be 'humanized,"' because of the relatively few and highly specialized human cells that are being implanted, Redmond said.

Still, it's research like Redmond's that upsets critics the most.

Stanford University bioethicist Christopher Scott said "the stuff that raises the most ethical concerns" are the experiments that implant human cells into animals' brains.

So far, Scott and others know of no researcher that has come close to putting enough human cells into animal brains to confer any signs of humanity, such as emotion.

In December, for instance, Parkinson's disease researchers at the Salk Institute in San Diego reported they had created mice with .01 percent human cells by injecting about 100,000 human embryonic stem cells per mouse, a trace amount that didn't remotely come close to "humanizing" the rodents.

Most scientists also argue that the "architecture" of animals' heads couldn't support a brain of mostly human cells. The animals are also wired differently and couldn't survive with a human brain.

Still, there's enough concern about human-animal mixing that the influential National Academy of Sciences addressed it last year when it issued guidelines for stem cell research.

The report endorsed research that co-mingles human and animal tissue as vital to ensuring that experimental drugs and new tissue replacement therapies are safe for people. But the report warned 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."

The report recommends that each institution involved in stem cell research create a formal, standing committee to specifically oversee the work, including experiments that mix human and animal cells.

Drawing ethical boundaries that no research appears to have crossed yet, the Academies recommend a prohibition on mixing human stem cells with embryos from monkeys and other primates. But even that policy recommendation isn't tough enough for some who advocate for formal regulations.

"You don't want a monkey with 95 percent of its brain cells being human," said Obasogie of the Center for Genetics and Society, "and to ensure that takes more than a recommendation."