Growth potential of the cells of permanent lines (HeLa, BHK/21, NRK)

A variety of culture parameters was tested to determine optimum growth conditions for the permanent cell lines HeLa, BHK/21 and NRK. Although the lines grew as well at clonal density as in mass culture, clonal analysis of cells transferred on coverslip fragments showed that only 71%-85% were able to produce permanent sublines. Kinetic analysis of the growth of individual clones showed that they varied widely in growth rate, despite continuous low density propagation designed to select out slowly growing cells. In addition, cytopathology was frequently evident in all lines studied, either when cultured at clonal density or under "ideal" conditions at moderate density. The results indicate that defective cells are continuously produced and that they exist in stable proportion in equilibrium cultures. These findings are at variance with claims that some permanent lines (i.e., HeLa) plate with 100% efficiency. Results are discussed in terms of the methodology used to determine plating efficiency, and also in terms of stochastic theories of cell kinetics, which predict the occurrence of cell death in permanent lines and explain the interconversion of permanent and limited cell lines observed in other systems.