June 19, 2007
One of the oldest and most controversial issues in cell biology is whether white blood cells can be transformed into connective tissue cells, such as bone and cartilage. As often happens in science, the data are open to a wide range of interpretation. NIDCR scientists and colleagues take a closer look at the subject in a paper published online in the journal Stem Cells on April 26, 2007 that uses a variety of cell separation techniques, cultivation conditions, and in-the-body, or in vivo, transplantation assays. They found that only three out of 66 human donors from diverse backgrounds had circulating in their blood true adherent connective tissue precursors, or cells with the capacity to differentiate into connective tissues. This provides strong evidence that circulating connective tissue precursors are absent in most people. Moreover, in people who had them, these precursor cells were “extremely scarce.” Interestingly, in their related studies with guinea pigs, the scientists found more circulating adherent connective tissue precursors. After culturing and allowing these cells to form distinct colonies, they determined that cells from only five out of 22 colonies had extensive ability to multiply. Of these five strains, two strains formed cartilage in culture, but interestingly, were unable to form bone upon in vivo transplantation. The researchers noted this marks the first demonstration of postnatal cartilage forming cells that circulate in the blood.