When his six-year-old daughter pulled out her baby tooth, Songtao Shi of the National Institute of Dental and Craniofacial Research in Bethesda, Md., washed it off to prepare it for the tooth fairy. Holding his daughter's partial tooth, the stem cell researcher noticed living tissue inside and wondered whether it might contain relatively young stem cells. Shi took the tooth to his lab and found that he was indeed able to isolate such cells from the tooth pulp left in the crown.
Extracting more stem cells from the lost baby teeth of seven- and eight-year-olds, Shi called the new group of cells SHED (stem cells from human exfoliated deciduous teeth). In the lab, the cultured cells grew quickly, forming sphere-like clusters indicative of a fast rate of proliferation not observed in stem cells isolated from bone marrow or adult teeth. Not only did they grow rapidly, but when implanted under the skin of immunocompromised mice, SHED induced bone formation--a feat that stem cells extracted from adult wisdom teeth could not accomplish. SHED cells also triggered neural cell formation in the brain and fat cell growth; stem cells from adult teeth, on the other hand, are not as good at neural cell generation and cannot trigger fat cell growth at all. A report describing these findings was published online this week by the Proceedings of the National Academy of Sciences.
One of the challenges of stem cell research is that nobody quite knows the extent to which they can be used to induce growth in tissues other than that from which they were extracted. In that regard, SHED cells could potentially work better than other types of stem cells because of their youth (and thus fast proliferation) and their demonstrated ability to induce the growth of several types of cells. "When kids' teeth fall out we can save them," Shi remarks. "If they need [the stem cells from] them in 20 years, there will be no immunorejection." Just what those needs might be, Shi cannot say. But considering that other researchers are already freezing stem cells from umbilical cords, he muses, "Why don't we save this one?"