Long-term retention of normal keratinocyte growth control mechanisms by many, but not all, hTERT-transductants. Cells were plated at low density in K-sfm medium, either in the presence (solid bar) or absence (stippled bar) of EGF (a) or in the presence (stippled bar) or absence (solid bar) of TPA (b), and counted 7 to 9 days later; growth under these conditions calculated as PD per day. Results shown are average of two experiments (standard error shown) except for LiF-Ep, LiF-Ep/TERT-1, and OKF6/TERT-2 in panel b, for which other experiments under slightly different conditions confirmed their TPA sensitivity (data not shown). PD levels of cells assayed: N, 50 PD (late life span); N/TERT-1, 135 P (RDI+68); LiF-Ep, 24 PD (mid-life span); LiF-Ep/TERT-1, 90 PD (RDI+55); OKF6, 37 PD (late life span); OKF6/TERT-1, 97 PD (RDI+45); OKF6/TERT-2, 115 PD (RDI+56); SCC-13 (∼50 PD).