HARVARD GAZETTE ARCHIVES

Postdoctoral fellow Kaylene Simpson: 'This is the first time it has been shown that one stem cell can give rise to all the cell types needed for normal breast development.' (Staff photo Stephanie Mitchell/Harvard News Office)

"Until now, no one has been able to take one cell and make it do everything involved in a fully-functioning, milk-producing breast," notes postdoctoral fellow Kaylene Simpson, who set up the experiment before moving to Harvard Medical School. "There were lots of technical obstacles to overcome and it was very difficult to attract funding at first."

Comparing the differences in development between normal and tumorous breasts could lead to new treatments that attack the earliest stages of breast cancer. Simpson also mentions the possibility of growing new breasts to replace those lost to surgery. As such medical applications become more likely, commercial interest in using stem cells to enhance breast size could also grow larger.

The idea of trying to produce a complete functioning breast from one adult stem cell originated with Geoffrey Lindeman and Jane Visvader at the Walter and Eliza Hall Institute of Medical Research in Melbourne. They enlisted Simpson to work with them because she had the technical expertise needed to extract individual cells from breast tissue, expertise acquired during her Ph.D. research at the Victorian Institute of Animal Science, also in Melbourne. The stem cell breast project took five years to complete.

A major challenge involved finding marker proteins that recognize and bind to the surface of breast stem cells in mice. This was necessary to separate them from the many other types of cells that make up a breast.

"We would like to find the same markers in human breasts," Simpson points out. "They could be used to identify stem cells in either live tissue or frozen samples. Clearly, that is the next step to take, and people in Melbourne are working on this now."

Wrecking tumor factories

Simpson compares breast tissue, mouse or human, to "a bunch of grapes in a big blob of fat." Separating stem cells from the blob turned out to be a tough problem.

"It took a long time because these cells don't like to be alone," she explains. "They are happiest in aggregates of 50 to 100 individuals. It required finding proteins that would bind to breast stem cells, something that had never been done before."

The marked stem cells were tagged with fluorescent dyes, then sorted by machines that recognize fluorescence. Finally, the cells were injected into young mice where they grew into new breasts. The procedure is described in detail in a report co-authored by Mark Shackleton, Lindeman, Visvader, Simpson and others, and published in the Jan. 5 issue of the scientific journal Nature.

"Basically, the newly grown tissues do everything that a normal breast does," Simpson says. "They respond to pregnancy, producing milk and milk proteins. This is the first time it has been shown that one stem cell can give rise to all the cell types needed for normal breast development."

Once human breast stem cells can be isolated, scientists will attempt to grow a human breast in a laboratory. The Australian researchers have also separated stem cells from tumorous mouse breasts, and they intend to identify the different genes involved in malignant versus normal growth.

Errant breast cells can become what researchers call "a tumor factory" where they perpetually divide and produce daughter cells. Such factories may be responsible for recurrence of human cancers after surgery and drug treatment or chemotherapy.

Chemotherapy works by killing cells that grow rapidly, typical of cancer cell behavior. But tumor factory cells grow more slowly and may survive for months or years after treatment.

The hope is that a close comparison between genes in normal and malignant breasts will identify the genes that make the difference. It then may be possible to design a drug that targets the faulty genes of rogue cells.

Customized breasts

Looking further ahead, genetic fingerprints might identify women with the rogue genes, making it possible to closely monitor, then treat them at the earliest stages of tumor development when therapy is most effective. Perhaps breast surgery could be avoided completely.

Also on the horizon is the possibility of injecting breast stem cells into women whose breasts have been partially or completely removed by surgery, in the hope of growing new breasts without the insidious tumor factory cells.

Successes like that would unavoidably lead to a demand for customized breasts. Simpson admits that at times her fellow researchers in Australia joked that such a possibility would make them rich some day. But now, she says, "Such an application is far from reality at this point."

Simpson currently works on another novel way to block breast cancer that is being studied in the laboratory of Joan Brugge the Department of Cell Biology at Harvard Medical School (see related story on page 13). She and her colleagues use a technique called RNA interference to find genes that regulate the movement of breast cancer cells, and thus the progression of malignancy in human tumors.

Simpson suspects that additional ways exist to benefit from the stem cell work she started in Melbourne. Using similar techniques, it should be possible to isolate stem cells that control development of other internal organs. "I'm hoping that the isolation of stem cells that produce such massively complex organs as breasts will become a model for growing organs, such as the lungs and pancreas," both sites of lethal cancers, she says.