Long-term growth of hTERT-transduced CD4⁺T cells compared with untransduced cells. The 12 hTERT-transduced clones were cultured in parallel with the untransduced clones, and the life span extension by hTERT was determined by the growth of the cultures far beyond the life span of the untransduced cells. The graph shows a representative example of the cumulative number of population doublings of hTERT-GFP–transduced CD4⁺ T-cell clone MoT-72 (□) and control GFP-transduced MoT-72 cells (•) during long-term culture. Transduction of clone MoT-72 was performed at the replicative age of 30 PDs (Table 1), and the graph shows the cumulative number of PDs of the cells during subsequent culture. At day 129 a new culture of the untransduced clone MoT-72 (▵) was started and cultured in parallel. Both GFP-transduced and untransduced T-cell cultures died after 100 days of culture, during which the cultures had reached approximately 39 or 42 PDs, respectively, whereas the hTERT-transduced cells continued to grow to more than 105 PDs. The graph is representative of 3 independent experiments performed with MoT-72 cells at approximately 30 PDs. Similar results were obtained in experiments of MoT-72 cells at approximately 34 PDs and in experiments of the 9 other T-cell clones, summarized in Table 1. † indicates death of the culture.