PDs and GFP expression of hTERT-transduced T lymphocytes. The progeny of one naive CD4⁺ T-cell clone was transduced with hTERT and a GFP control vector. After transduction cells were sorted for GFP expression and subclones with high and low GFP expression were obtained. Two subclones of each were selected and further expanded. GFP expression was analyzed and PDs were determined by counting viable cells once a week. The subclone transduced with hTERT showing high GFP expression exhibited a significantly higher proliferative potential compared to the subclone with low GFP expression (49.9 ± 2.3 PDs versus 29.9 ± 1.9 PDs). Dotted and solid vertical lines are shown for comparison; left of dotted line indicates no GFP expression, between dotted and solid lines indicates low levels of GFP expression, and right of solid line indicates high GFP expression. No difference in PDs was found for the GFP control-transduced T-lymphocyte clones with high or low GFP expression (24.9 ± 2.9 PDs versus 22.7 ± 2.3 PDs). Error bars indicate mean ± standard deviation of duplicate measurements.