using immunodeficient animals requires a specific facility, and
takes 3e4 months. In contrast, the cell growth analysis is not only
simple and economical, but also detects as few as 0.001% immortal
cellular impurities in hMSCs within 30 days, in case that the growth
properties of the immortal cells are comparable to those of HeLa
cells. Although immortality does not necessarily indicate tumorigenicity,
it is known to be closely associated with cell transformation
in many cases of tumorigenesis. Therefore, the present
study can be said to be the first scientific basis for the usefulness of
the cell growth analysis as one of tumorigenicity tests for hCTPs
derived from human somatic cells.