Researchers report today that they grew prostate glands—important for reproduction in male mammals—in mice using a single stem cell transplanted from the prostates of donor mice. The findings may pave the way to new therapies for prostate cancer, which strikes one in six men in the U.S.

This year, more than 186,000 men—mostly over age 65—will be diagnosed with this form of cancer, according to the National Cancer Institute (NCI) in Bethesda, Md; some 28,000 men lose their battle with the disease each year.

Identifying the cells responsible for prostate malignancies has been a major challenge for researchers. Given the ability of stem cells to divide indefinitely, investigators have debated their possible role in the development of the disease. Defining which cells in the prostate are actually stem cells, however, has been difficult.

A stem cell is generally characterized by the presence of various proteins—or cell markers—on its outer surface. Three markers had previously been associated with stem cells in the prostate; these researchers discovered an additional marker dubbed CD117 that allowed them to isolate individual stem cells from the glands in adult mice.

To confirm that these cells were, in fact, stem cells, the scientists transferred them into the kidneys of adult mice. Within eight weeks, the researchers observed characteristic prostate tissue architecture and could measure the secretion of prostate-specific chemicals from the growing transplants.

By homing in on the stem cells, researchers can now examine how this cell population helps regulate growth in the prostate, says Leisa Johnson, a molecular biologist at Genentech, Inc., in South San Francisco, Calif., and co-author of the study appearing in Nature. Comparing the markers on these stem cells with those on the surfaces of cancer cells, Johnson adds, will also help scientists determine if stem cells contribute to prostate malignancies.

"If the CD117 cell population does lead to tumor initiation or cancer reoccurrence, this cell marker could become a therapeutic target," she says. Preliminary work already indicates that a small population of CD117 cells exists in the human prostate.

Kathleen Kelly, a cancer biologist at NCI, is optimistic that the work will enhance understanding of the basic mechanism of the disease. But she warns that "it is still hard to say what this work means for therapy," because the function of CD117 is not yet known.

By the way, don't expect the prostate-making mice to spark regeneration schemes for the reproductive gland. Given that no clear need exists for it, says Arnon Krongrad, founder and medical director of The Krongrad Institute for minimally invasive prostate surgery in Aventura, Fla., "most men would be pleased to get rid of the prostate, a potential source of symptomatic enlargement, painful inflammation and potentially fatal cancer."