Blood Stem Cells Originate in the Placenta

FRIDAY, March 7 (HealthDay News) — Blood stem cells, which later differentiate into all types of blood cells, originate and are nurtured in the placenta, a U.S. study finds.

This finding may help researchers replicate the specific embryonic microenvironment necessary to grow blood stem cells in the lab so doctors can treat patients with diseases such as leukemia and aplastic anemia, said senior author Dr. Hanna Mikkola, a researcher in the Eli and Edythe Broad Center of Regenerative Medicine and Stem Cell Research at the University of California, Los Angeles (UCLA).

"It was a big mystery, where these cells originated. This is the first time we can really say definitively that blood stem cells are generated in the placenta. There's no more speculation," Mikkola said in a prepared statement.

The discovery, reported in the March 6 issue of Cell Stem Cell, was made in research with mice. The researchers are now working to replicate it 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. We can learn that by studying what happens during embryonic development," said Mikkola, an assistant professor of molecular, cell and developmental biology and a researcher at UCLA's Jonsson Comprehensive Cancer Center.

In previous research, Mikkola and her colleagues found the placenta contained a large supply of stem cells, but the researchers weren't sure if these stem cells were created in the placenta or originated elsewhere and migrated to the placenta to self-renew.

In this new study, Mikkola's team examined a unique mouse model, a mouse embryo without a heartbeat. Because there was no blood circulation, the researchers were able to find the blood stem cells at their point of origin in the placenta.

"Using this model, we identified that the placenta has the potential to make hematopoietic [blood] stem cells with full differentiation ability to create all the major lineages of blood cells. The placenta acts as a sort of kindergarten for these newly made blood stem cells, giving them the first education they need," Mikkola explained.

—Robert Preidt

SOURCE: University of California, Los Angeles, news release, March 6, 2008

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