Telomerase activity in vitro represents a radiation-inducible function. To test this effect after irradiation in vivo, we measured telomerase activity in peripheral blood mononuclear cells (PBMC) of 25 patients with leukemia or lymphoma before and 1 h after whole body irradiation. Telomerase activity of the patients was compared to telomerase activity in PBMC of 15 healthy volunteers. Peripheral blood of the patients was taken before and 1 h after the first fraction of whole body irradiation (2 Gy). Blood samples of the volunteers were irradiated ex vivo with 2 Gy. After Ficoll-Paque density gradient centrifugation telomerase activity of 104 PBMC per sample was measured using the telomerase PCR ELISA method. No age-dependence of telomerase activity was detected for both the volunteer and the patient group. Telomerase activity in patients was not statistically significantly increased compared to healthy individuals, and this parameter was also no prognostic factor for patient survival. After whole body irradiation an induction of telomerase activity was observed for only 7 patients (28%), or in PBMC of 2 volunteers (13%), respectively. In patients with radiation-inducible telomerase activity, a slightly better survival was indicated, but this difference did not reach statistical significance. The feasibility to assess in vivo radiation-induction of telomerase activity in PBMC of leukemia or lymphoma patients was demonstrated. An unexpectedly low number of whole body irradiated patients displayed this phenotype, and the treatment impact of telomerase upregulation in PBMC upon radiation exposure needs to be further analyzed.

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