Debate over creating a man-mouse hybrid
Human stem cells to be injected into mice to test its quality
NEW YORK - A group of American and Canadian biologists is debating whether to recommend conducting stem-cell experiments which would involve creating a human-mouse hybrid.
The goal would be to test different lines of human embryonic stem cells for their quality and potential usefulness in treating specific diseases. The best way to do that, some biologists argue, is to see how the cells work in a living animal.
For ethical reasons, the test cannot be performed in people.
But if the human stem cells were tested this way in mice, any animals born from the experiment would be chimeras - organisms that are mixtures of two different kinds of cells - with human cells distributed throughout their body.
Though the creatures would probably be mice with a few human cells obeying mouse rules, the outcome cannot be predicted.
A mouse with a brain made entirely of human cells would probably be discomforting to many people, as would a mouse which generated human sperm or eggs.
Dr Irving Weissman, a stem-cell expert at Stanford University, said that making mice with human cells could be 'an enormously important experiment' but, if done carelessly, could lead to outcomes that are 'too horrible to contemplate'.
He gave, as an extreme example, the possibility that a mouse making human sperm mating accidentally with a mouse which had made its eggs from human cells.
Stem cells, the clay from which all tissues of the body are generated, hold high promise as an all-purpose material for repairing many of the degenerative diseases of old age, such as Parkinson's, cancer and heart disease.
Some scientists say such experiments would be of great value and could be conducted with human stem cells engineered so that they could not produce brain or reproductive cells.
The proposal for the experiment grew out of a meeting held on Nov 13 at the New York Academy of Sciences.
The purpose of the meeting was to discuss setting quality standards for new lines, or colonies, of human embryonic stem cells being developed around the world.
In one test discussed, human embryonic stem cells would be injected into an early mouse embryo, when it was still a small ball of cells called the blastocyst.
Scientists would then see if the human stem cells showed up in all the tissues of the mouse's body. This ability, known as pluripotentiality, is the hallmark of a true embryonic stem cell.
Injection into another mouse's blastocyst is the standard test for mouse embryonic stem cells which, like human embryonic stem cells, are derived from a small pool of all-purpose cells a few days after the fertilised egg has started to divide.
No one knows yet if human embryonic stem cells would survive at all in a mouse blastocyst. But if they did, and contributed to all the mouse's tissues, this would be a useful test for the many claimed human embryonic stem cell lines being developed around the world.
But one participant at the meeting, Dr Janet Rossant of Mount Sinai hospital in Toronto, said she did not consider the test necessary.
Stanford's Dr Weissman, who was not at the meeting, said that undesirable outcomes could be avoided by deleting certain genes from the human embryonic stem cells before injecting them into a mouse blastocyst.
But he added that such procedures should be reviewed carefully. --The New York Times |
