In 1972, a group of forward-thinking conservationists in San Diego began freezing skin samples from endangered species. The hope was that science would eventually find a way to use the cells to help revive these fragile populations.

Jeanne Loring and collaborators at Scripps Research Institute have taken a key step toward fulfilling that hope by creating stem cells from frozen skin cells of two such species—the silver-maned drill monkey and the northern white rhinoceros.

In the near term, the researchers plan to build a frozen zoo of stem cells that scientists can use to study the animals' genomes, and perhaps to create stem-cell therapies for the animals. (Drill monkeys living in captivity often suffer from diabetes, a highly active area of research in the human stem-cell field.)

In the longer term, the researchers hope to be able to use the cells to create sperm and eggs, which would be incorporated into breeding programs to boost the genetic diversity of severely limited populations; the white rhinoceros is on the verge of extinction, with only seven animals alive today. They haven't bred in years.

"To think of the foresight they had in the 1970s to start this program," says Loring, director of the Center for Regenerative Medicine at Scripps. At that point, "no genome had been published, and the concept of this ever happening was science fiction." Her team aims to generate stem cells for at least 10 other species, including snow leopards and some species of elephants. San Diego's "Frozen Zoo" houses tissue samples from more than 800 species.

To create the stem cells, Inbar Friedrich Ben, a postdoctoral researcher in Loring's lab, used a technique first developed in 2007 called induced pluripotent stem (iPS) cell reprogramming. A handful of genes that are normally active in the developing embryo are expressed in a differentiated cell, such as a skin cell, causing that cell to revert back to its undifferentiated state.

Much to their surprise, the human genes that are typically used to reprogram human cells could also reprogram skin cells from both the monkey and the rhinoceros, though at a much lower efficiency. Still, the reprogrammed cells showed the defining characteristics of induced pluripotent stem cells; they could both differentiate into various cell types and generate more of themselves. The research was published this week in Nature Methods.