HESCs in Mouse Brains
HESCs in Mouse Brains
Scientists at the Salk Institute in San Diego have transplanted human embryonic stem cells into the brain of embryonic mice. Each fetus received about 100,000 human stem cells before it was replanted in its mother’s uterus. Several hundred of the stem cells (100 would be .1%) survived to mouse adulthood. According to a San Diego Union Tribune story,
The rodents' brain cells apparently prompted the human embryonic stem cells to morph into cells approximating the size and shape of typical mouse neurons, [Fred]Gage said. Somehow, communication between the two species' cells prompted the human ones to suppress genes that would have otherwise led to the growth of human-looking brain cells.The article lays out several research angles for this kind of work: for example, scientist could see if mice with Alzheimer’s transfer the disease to the healthy new stem cells, or, vice-versa, if diseased stem cells cause healthy mouse cells to become diseased. Research at Stanford is being done involving trying to embryonic stem cells to be human neurons in mice.
The story is widely reported, and I want to include snippets from a few other sources. The San Francisco Chronicle quotes the lead researcher, Fred Gage, as saying, “Is it a diseased environment that influences nondiseased cells, or are diseased cells hurting a healthy, intact environment?” The Chronicle also outlines some of the other ethical issues with a “chimera,” or an animal which is a mixture of different animal types. In this experiment, the mice were confined to separate cages so there was no possibility they could reproduce. The Chronicle article concludes by saying,
Their work found that a developing mouse brain can tolerate a few human cells, and remain a mouse brain, because the human cells proved to be incapable of restructuring the host.So far, no mice with human brain structures.
The Chronicle story also quoted a critic of embryonic stem cell research:
“Where are the lines, and how do we decide where the lines are?” wondered Jennifer Lahl, a bioethicist at the Center for Bioethics and Culture Network in Oakland. “What if someone decides to start doing this for art? I'm glad science has progressed to the level that we can do this incredible stuff, but we also have to be a lot more thoughtful about it.”
A Washington Post article adds the information that the stem cells were not rejected by the mouse immune system, nor did they turn into tumors. Instead they migrated to the mouse forebrain and connected to neurons. It is unknown if the firing patterns were mouse patterns or human patterns.
An AP story reprinted widely, including on the MSNBC website, says,
Researchers are nevertheless beginning to bump up against what bioethicists call the “yuck factor.” Three top cloning researchers have applied for a patent for fusing a complete set of human DNA into animal eggs in order to manufacture human embryonic stem cells. Scientists say mixing human and animal tissue is vital to ensuring new drugs and tissue replacement therapies are safe.The story goes on to describe other experiments that have been done combining the tissues or cells of other species.
Putting human DNA into a cow egg might be an attempt to get around the issues of embryonic stem cell research, since there would be no human ova involved. But I suspect anti-embryonic stem cell researchers would say that the human DNA still makes it unethical.
Is a human defined by DNA? By sperm and egg? If you can have one without the other, what do you have?
Human cells have been transplanted into lab animals for years, so this is not exactly new. But additional concerns are being raised because brain cells are involved.
Is a human being a pattern of brain cells?
The study raises a lot of issues, in part because it highlights human perceptions about what is “natural.” The “yuck factor” in cross-species cell mixing is almost akin to an incest taboo. When do these feelings indicate a line has been crossed? When are they culturally conditioned beliefs with no rational basis? How is yuckiness weighed against research benefits?
All the media I looked at reported that the National Academy of Science issued a report in April attempting to establish ethical guidelines for embryonic stem cells used in “chimera” research (as part of its general guidelines for hESC research). The press release on the report has links to the full report and also information on how to get print copies.