Normal human cementum-derived cells: isolation, clonal expansion, and in vitro and in vivo characterization.

Cultures of primary human cementum-derived cells (HCDCs) were established from healthy premolar teeth extracted for orthodontic reasons. Cementum was manually dissected, fragmented, and digested twice with collagenase. Following a thorough wash to remove liberated cells, the remaining cementum fragments were plated in Dulbecco's modified Eagle's medium/F12 medium containing 10% fetal bovine serum. Discrete colonies that contained cells exhibiting fibroblast-like morphology were visible after 14-21 days of culture. When the colonies became sufficiently large, cells from individual colonies were isolated and subcultured. Cementum-derived cells exhibited low levels or no alkaline phosphatase activity and mineralized in vitro to a lesser degree than human periodontal ligament (PDL) cells and human bone marrow stromal cell (BMSC) cultures. To study differentiation capacities of HCDCs, cells were attached to hydroxyapatite/tricalcium phosphate ceramic and transplanted subcutaneously into immunodeficient mice. The transplants were harvested 3, 6, and 8 weeks after transplantation and evaluated histologically. In human BMSC transplants, new bone tissue was formed with a prominent osteoblastic layer and osteocytes embedded in mineralized bone matrix. No osseous tissue was formed by PDL cells. Of six single colony-derived strains of HCDCs tested, three formed a bone-like tissue that featured osteocyte/cementocyte-like cells embedded within a mineralized matrix and which was lined with a layer of cells, although they were somewhat more elongated than osteoblasts. These results show that cells from normal human cementum can be isolated and expanded in vitro. Furthermore, these cells are capable of differentiating and forming mineralized tissue when transplanted into immunodeficient mice.