Telomerase inhibition induces telomere attrition in HTLV-I–infected cells. (A) Telomerase activity (expressed as telomeric product generated, TPG), measured by TRAP assay in HTLV-I cell lines in absence of or presence of telomerase inhibitors AZT (50 μM) and ddG (10 μM) for 72 hours. (B) Correlation between telomerase activity (TPG) and survival of AZT-treated HTLV-I cell lines (in weeks). (C) Inhibition of telomerase activity by AZT in the HTLV-I–transformed MT-2 cell line untreated or treated with AZT for 18 weeks. (D) Southern blot analysis of telomere shortening following AZT treatment.