Establishment of a clonal human mesenchymal cell line that retains multilineage differentiation capacity from a spinal hamartoma

We isolated a single-cell-derived cell line from a spinal hamartoma, a which occurred in a newborn boy and was associated with a rudimentary limb. The maternal cells (HHC-7) differentiated into osteoblasts, chondrocytes, adipocytes, and skeletal muscles when they were cultured in differentiation-inducing media specific to each mesenchymal cell. We isolated a single-cell-derived clonal cell line (Clone K) after transfection with SV40 T antigen. These cells expressed CD73 and CD117, while being negative for expression of CD45. Clone K cells cultured in an osteogenic differentiation medium increased ALP activity and expressed mRNAs for Runx2 and osteocalcin. Treatment with rhBMP-2 induced Clone K cells to differentiate into both osteoblasts and chondrocytes. These cells expressed mRNAs for Sox9 and aggrecan in addition to osteogenic markers. Culture in an adipogenic differentiation medium induced Clone K cells to differentiation into adipocytes, which expressed mRNAs for PPARgamma2 and a2P. Clone K cells cultured in a serum-depleted medium generated desmin-positive cells and expressed MyoD1 mRNA. Clone K cells exhibited numerous alpha-smooth muscle actin-positive cells; however, treatment with rhBMP-2 decreased their number. Clone K cells, transplanted with a carrier containing rhBMP-2 into the muscles of SCID mice, generated ectopic endochondral bone formation. In these tissues, several osteoblasts and chondrocytes expressed SV40 T antigen, indicating their Clone K cell origin. Thus, Clone K cells are useful tools for analyzing the characteristics of human multipotential mesenchymal progenitors.