“…Previously, we had shown that in the pre-immortal HA1 clone, telomere length declines with cell division and telomerase remains inactive until the cells reach proliferative crisis, while in immortal HA1 cells telomere length stabilizes and telomerase is activated (Counter et al, 1992;Avilion et al, 1996). Recently, we also found that up-regulation of the mRNA encoding the catalytic subunit of human telomerase, hTERT (Meyerson et al, 1997;Weinrich et al, 1997;Nakamura and Cech, 1998), coincides with the emergence of immortal HA1 cells (Meyerson et al, 1997).…”