A general method for determining the replicative age of normal animal cell cultures

The percentage of cells capable of forming colonies of at least a given size has been found to provide a reliable estimate of the remaining doubling potential of several human diploid fibroblast cell lines and for chick embryo fibroblasts. In five independently derived cell lines of human diploid fibroblasts we have found the same linear relationship between population doublings remaining and the percentage of cells able to form colonies of at least 16 cells. For chick embryo fibroblasts there is a linear relationship between the percentage of cells forming colonies of 64 or more cells and remaining proliferative potential. When human diploid fibroblasts were grown in medium containing hydrocortisone at 5 microgram/ml the increased in vitro lifespan was reflected in the colony size distribution long before the end of the in vitro lifespan.