The research grew out of Zambidis' interest in understanding the complex biological processes of blood development and the transformation of embryonic stem cells into the various types of cells that make up the human body.
Hemangioblasts make the body's earliest form of blood in the fetal yolk sac, which nourishes a fertilized egg, and later in the fetal liver and bone marrow. However, because human embryonic cells disappear early in gestation, their role in the early production of blood could not, to the researchers' knowledge, be studied in humans because scientists had no way to identify these human progenitor blood stems cells to follow their development. The scientists suspected they existed in humans, however, because they have been found in mice and zebra fish.
To find the blood stem cell, Zambidis' team grew human embryonic stem cells in culture and fed them growth factors over 20 days. Each time the cell colonies expanded, the researchers sampled individual cells, searching for ones capable of making both endothelial and blood cells, the hallmark of hemangioblasts.
They plucked the newly discovered hemangioblasts from culture dishes, grew them in conditions that Zambidis and his team developed to speed replication, and tested cells for their ability to make endothelial and blood cells. Cells capable of making endothelial cells and all the elements of blood (platelets, and white and red cells) were specifically marked with ACE on their outer surface.
The researchers found not only that ACE was a marker for
|Contact: Valerie Mehl|
Johns Hopkins Medical Institutions