Next, we examined the growth rates of the contaminated cells
(Fig. 3A). They were comparable to that of HeLa 0 at P ¼ 5, and got
significantly increased at P ¼ 6 (HeLa 1000 and HeLa 100) or P ¼ 7
(HeLa 10). These results indicated that the gross proliferation rate
was not influenced by the spiked cells at P ¼ 5 and then the population
of HeLa cells in hMSCs increased in dose- and timedependent
manner. Eventually, the growth rate (doubling/day) of
the contaminated hMSCs increased, and then reached plateau. The
average growth rate of the contaminated cells at P ¼ 9 and 10 was
0.73, suggesting that the growth rate of HeLa cells was approximately
0.7 in this culture condition. The average growth rates of the
three lots are plotted along the passage number in Fig. 3B. The
growth rates of HeLa 1000 and HeLa 100 at P ¼ 7 and HeLa
10 at P ¼ 8 were significantly increased compared with the growth
rates at P ¼ 5 (*P < 0.05, two-way repeated measures ANOVA and
Student-NewmaneKeulis test). These results indicate that the cell
cultures longer than P ¼ 7 (about 20 days) and P ¼ 8 (about 30 days)
detect cross-contaminations of 100 (0.01%) and 10 (0.001%) HeLa
cells, respectively, assuming that 106 hMSCs were contaminated at
P ¼ 5.
Abbreviations
hCTP human cell-processed therapeutic product
PSC pluripotent stem cell
hMSC human mesenchymal stem cell
STR short tandem repeat
P ¼ n passage n
PBS phosphate buffered saline
RT room temperature
HPV human papillomavirus