Inhibition of telomerase activity by ectopic DN-hTERT expression. Telomerase activity in a culture of polyclonal T cells isolated from donor PBMCs transduced with DN-hTERT (Asp868Ala, Asp869Ala)–GFP, hTERT-GFP, or control GFP after 2, 4, and 6 days of stimulation. Telomerase activity was detected in control GFP-transduced cells 2 to 4 days after stimulation and was absent in the DN-hTERT–transduced cells. In hTERT-transduced cells telomerase activity was present at all time points analyzed. Each lane shows the telomerase activity present in 2000 cells analyzed by the TRAP assay. K562 cells were tested as a positive control for telomerase activity. Results are representative of 3 experiments.