Updated 9:16 PM ET
February 23, 2001
By Andrew Quinn
SAN FRANCISCO (Reuters) - U.S. researchers have produced laboratory mice with human brain cells, marking a potential step toward developing treatments for human brain disease like Alzheimer's but promising to fuel fresh debate over the evolving ethics of bioengineering.
The research at California biotechnology company StemCells Inc breaks new ground by demonstrating that human brain stem cells can be induced to grow within a mouse's skull, scientists said Friday.
"We are not recreating a human brain. We're really just trying to understand how these stem cells can function, and how they can be used in the treatment of specific diseases," said Ann Tsukamoto, vice president of scientific operations at StemCells Inc.
Irving Weissman, a Stanford university professor involved in the two-year research project, said the next step could be to produce mice with brains made up almost entirely of human cells -- although he said there would have to be a thorough ethical review before this step is taken.
"You would want to ask the ethicist what percentage of the brain would be human cells before you start worrying, and if you start worrying, what would you start worrying about," Weissman said.
The California study involved isolating human stem cells in the laboratory and then introducing them into mice. As the mice matured, the human stem cells -- "master cells" that can develop into any other type of cell -- grew into a full range of specialized cells throughout each mouse brain.
"It looks like human cells can follow the developmental instructions put in by the mouse brain. They are making human components in what is clearly a mouse brain," Weissman said.
The researchers believe that these mice could be used to test treatments for human brain diseases such as Parkinsons and Alzheimer's, although these tests have not yet been undertaken.
Tsukamoto added that the experiment also demonstrated that StemCell Inc's process for isolating and developing human stem cells was viable, and that cell banks could be established for future transplantation into humans.
"We're of course moving this into the development phase, and looking at which disease indications these cells would be best used for in preclinical trials," she said.
Both scientists stressed that their research, while marking a new breakthrough in the controversial world of stem cell research, was in no way aimed at blurring the lines between human and animal.
But Weissman added that he had already requested a review panel to look at the research to determine if there may be ethical problems in taking the work further.
"It is not not the
objective to go make mice with human brains," Weissman said. "(But) it
is in the domain of the ethicists, not the experimenters, to figure out
what our limits are."