Solving a long-standing biological mystery, UCLA stem cell researchers have discovered that blood stem cells, the cells that later differentiate into all the cells in the blood supply, originate and are nurtured in the placenta.

The discovery may allow researchers to mimic the specific embryonic microenvironment necessary for development of blood stem cells in cell culture and grow them for use in treating diseases like leukemia and aplastic anemia, said Dr. Hanna Mikkola, a researcher in the Eli and Edythe Broad Center of Regenerative Medicine and Stem Cell Research and senior author of the study.

“It was a big mystery, where these cells originated,” said Mikkola, an assistant professor of molecular, cell and developmental biology. “This is the first time we can really say definitively that blood stem cells are generated in the placenta. There’s no more speculation.”

The study is published March 6, 2008 in the journal Cell Stem Cell. Researchers in Mikkola’s lab are working now to replicate this work, done in mouse models, in humans.

“If we want to fully harness the potential of embryonic stem cells to treat disease, it’s critical for us to learn how to make tissue specific stem cells,” said Mikkola, who also is a researcher at UCLA’s Jonsson Comprehensive Cancer Center. “We can learn that by studying what happens during embryonic development.”