But there was excitement over this curious cell. It would be great for studying how normal embryos developed, some said. It would be great for figuring out how cancers form.
Others like Pierce reckoned: Maybe you could cure cancers by getting malignant cells to turn into skin or muscle instead of spreading.
"It was a model of both cancer biology and developmental biology, and for a while we were selling it as the answer to everything in the world," Solter says.
As it turned out, these little round cells didn't end up providing cures for cancer or answers to all of developmental biology's mysteries. But they left a legacy rich with promise.
First, scientists such as Martin learned to grow them and study them in labs.
That done, the scientists turned their attention to another target: growing real embryonic stem cells, cells that had never been a cancer in an animal but that came from the earliest of early mouse embryos. Pure lines that could live and divide and thrive in dishes.
Research Success Strikes Twice
In 1981, two groups reported success: Martin Evans, then of the University of Cambridge in England, and Martin at UC San Francisco. (Evans, who published a few months before Martin, shared this year's prestigious Lasker award for basic medical research.)
To get her precious lines, Martin said, she first flushed a whole load of embryos from mice. Then she took the tiny, 31/2-day-old balls of cells and chemically treated them to find the few that were destined to become the fetus.
She placed her treated cells in dishes along with other, skin-like cells known as "feeder cells," which ooze hormones essential for stem cells' growth. She tended her dishes in incubators at a balmy 99 degrees Fahrenheit. And she waited.
A week later, she saw tiny colonies of cells growing among her fibrous feeder cells--real embryonic stem cells.
"There have been a couple moments in my career when I've been really excited, and one was the night I saw those stem cells growing," Martin says.
Mouse embryonic stem cells have had a huge impact in basic, nonmedical research: they became essential ingredients in a powerful method that revolutionized the way scientists could figure out the function of genes.
And, eventually, scientists repeated with human embryonic tissue what had been done in mice. In 1998, scientists at the University of Wisconsin reported they had isolated human embryonic stem cell lines.
Given all that came before, "the development of human stem cells is really not surprising at all," Pierce says.
Today, researchers are focused like never before on figuring out how embryonic stem cells move along different developmental paths and end up as different types of tissues.
Meanwhile, no one yet knows what wild, genetic mistake caused cells in Stevens' mouse strain to divide and behave like cells of a very early embryo. But in a fitting legacy to Stevens, a former student of his--Joe Nadeau, of Case Western Reserve University--says he has narrowed down one of the genes involved to two possibilities, out of the 30,000 to 40,000 in the mouse genome.
"We should know the answer soon," Nadeau says.
