STABILIZATION OF SHORT TELOMERES AND TELOMERASE ACTIVITY ACCOMPANY IMMORTALIZATION OF EPSTEIN-BARR VIRUS-TRANSFORMED HUMAN B-LYMPHOCYTES

We have measured telomere length and telomerase activity throughout th e life span of clones of human B lymphocytes transformed by Epstein-Ba rr virus. Shortening of telomeres occurred at similar rates in all pop ulations and persisted until chromosomes had little telomeric DNA rema ining. At this stage, some of the clones entered a proliferative crisi s and died. Only clones in which telomeres were stabilized, apparently by activation of telomerase, continued to proliferate indefinitely, i .e., became immortal. Since loss of telomeres impairs chromosome funct ion, and may thus affect cell survival, we propose that telomerase act ivity is required for immortality. We have now detected this enzyme in a variety of immortal human cells transformed by different viruses, i ndicating that telomerase activation may be a common step in immortali zation.