Expression of endogenous hTERT upon stimulation during culture. (A) Wild-type MoT-81 cells and hTERT-transduced cells of identical age were stimulated with anti-CD3 and anti-CD28 mAbs, and the expression of endogenous hTERT at day 0, 1, 3, 5, 7, and 11 was determined by RT-PCR. All samples were tested for HPRT expression to check for equal amounts of RNA. (B) RT-PCR analysis of endogenous and ectopic hTERT expression in wild-type BOY JF161 cells after approximately 36 PD and in hTERT-GFP–transduced cells after more than 60 PD.