From myth to reality

Boston.com / News / Boston Globe / Health / Science / By Carolyn Y. Johnson

Scientists can create animals with the cells of other species, but are these chimeras medical marvels or high-tech monsters?

"Herds of pigs are grown with partly-human livers in the hopes of solving the organ-transplant shortage. Mice with human cells are used as the new ''guinea pigs" for testing drugs or figuring out disease. Human brain cells are grown inside mouse skulls to help better understand diseases like Parkinson's and Alzheimer's.

Scientists are using such chimeras -- animals whose bodies are a mosaic, with their own cells intermixed with those of another animal -- to model diseases, test drugs on live human cells, and harvest organs for transplant.

A seven-year-old patent application for a chimpanzee-human mix, the ''humanzee," was turned down in February, with patent officers calling on Congress for guidance. Canada banned the creation of all chimeras last year. And the National Academy of Sciences is set to release ethical guidelines this month for researchers who use stem cells to create chimeras. .

Animal rights advocates argue that any manipulation of animals for human benefit -- whether for dinner or for research -- is immoral.

Christian teaching holds that the Bible gives people dominion over animals.

The problem arises, Stevens said, when scientists fundamentally alter what it means to be human or animal. ''If you give an animal a human brain; if you give an animal human reproductive organs; if you make a human embryo that's not fully human -- that crosses the ethical, moral, and biblical line."

The Roman Catholic Church has grave concerns that chimera research may create beings without a clear moral status. ''I think it would be basically immoral to create a human whose status we could not determine. We'd have an unresolvable dilemma about how to treat this animal," said Richard Doerflinger, deputy director of the secretariat for pro-life activities at the US Conference of Catholic Bishops.

Four years ago, Irving Weissman, a stem cell biologist at Stanford, created a mouse with human neurons in its brain, hoping that such a living model would provide insights into disease like Parkinson's and Alzheimer's.

The human neurons made up about 1 percent of the mouse brain, and were alive, but it was unclear whether they were functioning. He suggested another project -- creating a mouse with 100 percent human nerve cells in its brain.

Scientists agree that human brain cells growing in a mouse are unlikely to humanize a mouse because of the vast differences in skull size and brain architecture. But in a closely related animal, like a chimp, the threat of an animal floating somewhere between human and animal becomes more serious.

''What is essentially human is really debased," Alfonso Gomez-Lobo, a member of the President's Council on Bioethics, said in March. ''I often imagine what it would be like to wake up one day only to realize that I have the body of a chimpanzee."

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