Mighty Mice

They may not look as strange as a Minotaur or a mermaid, but some of the mice used in today's research labs are every bit as wondrous as those mythical combinations of animals and humans. In 1988 two California immunologists announced that they had transplanted human immune-system tissues and cells into mice, causing the rodents to manufacture human antibodies and certain types of white blood cells. Since that pioneering effort, "humanized" mice have become invaluable research tools, particularly in the fight against AIDS and other viral diseases.

New experiments indicate that tissues from many different human organs can be put into mice, which should eventually enable researchers to use the animals for studying a variety of ailments. "The implications are really extraordinary," says Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases.

In a typical project using the method devised by Dr. J. Michael McCune of San Francisco General Hospital, researchers take segments of tissue the size of rice grains from the liver, thymus and lymph nodes of an aborted human fetus and implant these cells under the kidneys of mice. (The strain of mouse used lacks an immune system and thus does not reject the foreign tissue.) Within a month or two, the tiny clusters of transplanted cells begin to function like miniature human organs and produce immune-system cells. Since the AIDS virus attacks such cells, the mice can be infected with the disease. This enables researchers to study how AIDS progresses and to test potential drug treatments.

In other research, scientists are equipping mice with snippets taken from a human lung, intestine or pancreas. "I think we could grow and study just about any organ in the mouse," says McCune. "It's just a matter of finding the place to grow it."